111
ENTROPY WS 1
14
16
The equation for the reaction of CO2 and H2O to produce glucose, C6H12O6, and O2 is shown
below.
6CO2(g) + 6H2O(l)
C6H12O6(s) + 6O2(g) ΔH = +2879 kJ mol–1; ΔS = –256 J K–1 mol–1
Standard entropies are given in the table below.
Substance
CO2(g)
H2O(l)
O2(g)
214
70
205
S o / J K–1 mol–1
(a) (i)
Calculate the standard entropy of glucose.
S o = ....................................... J K–1 mol–1 [2]
(ii)
Calculate ΔG, in kJ mol–1, at 25 °C.
Show all your working.
ΔG = ........................................... kJ mol–1 [2]
(iii)
Explain why this reaction is not feasible at any temperature.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [1]
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ENTROPY WS 1
H2O(s)
H2O(l)
H2O(l)
H2O(g)
ΔH = +6.01 kJ mol–1
ΔH = +40.7 kJ mol–1
112
8
Standard entropies of H2O in its three physical states are given in the table below.
2(b) Energy changes for the melting and boiling of H2O are shown below.
H2O(s)
H2O(l)
H2O(g)
H2O(l)
ΔH = +6.01 kJ mol–1
H2O(s)
–1 mol–1
–1
+48.0
+70.0
+188.7
S o / JHK
H2O(g)
ΔH
= +40.7 kJ mol
2O(l)
Standard
entropies
of H2O in its three physical states are given in the table below.
(i) Explain
the following:
•
•
(i)
When water melts or boils,
ΔH is positive
H2O(s)
H2O(l)
H2O(g)
When water melts or boils, S o increases.
+48.0
+70.0
+188.7
S o / J K–1 mol–1
In your answer, you should explain why the increase in S o is much greater when water
boils than
water melts.
Explain
thewhen
following:
• ...........................................................................................................................................
When water melts or boils, ΔH is positive
•
When water melts or boils, S o increases.
...........................................................................................................................................
In your answer, you should explain why the increase in S o is much greater when water
...........................................................................................................................................
boils
than when water melts.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [3]
...........................................................................................................................................
(ii)
Using
the data in the table above, show that ice melts at 0 °C (at standard pressure).
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [3]
(ii)
Using the data in the table above, show that ice melts at 0 °C (at standard pressure).
[3]
© OCR 2013
[Total: 16]
[3]
© OCR 2013
CEDAR COLLEGE
[Total: 16]
ENTROPY WS 1
...........................................................................................................................................
113
......................................................................................................................................
[2]
3(b) The feasibility of the reaction between NO2 and O3 is influenced by the enthalpy change and
entropy change of the reaction and the temperature.
2NO2(g) + O3(g)
(i)
N2O5(g) + O2(g)
ΔH = –198 kJ mol–1
ΔS = –168 J K–1 mol–1
Explain why this reaction has a negative entropy change.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [2]
(ii)
Calculate the value of ΔG, in kJ mol–1, at 25 °C for the reaction of NO2 with O3.
ΔG = ........................................... kJ mol–1 [3]
(iii)
State and explain how the feasibility of this reaction will change with increasing
temperature.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [2]
[Total: 17]
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ENTROPY WS 1
114
16
46
Free energy changes can be used to predict the feasibility of processes.
(a) Write down the equation that links the free energy change with the enthalpy change and
temperature.
.............................................................................................................................................. [1]
(b) You are provided with equations for five processes.
For each process, predict the sign of ΔS.
process
2CO(g) + O2(g)
2CO2(g)
NaCl(s) + (aq)
NaCl(aq)
H2O(l)
sign of ΔS
H2O(s)
Mg(s) + H2SO4(aq)
CuSO4(s) + 5H2O(l)
MgSO4(aq) + H2(g)
CuSO4•5H2O(s)
[2]
(c) Ammonia can be oxidised as shown in the equation below.
4NH3(g) + 5O2(g)
4NO(g) + 6H2O(g)
Standard entropies are given in the table below.
substance
–o–
S /J
K–1
mol–1
NH3(g)
O2(g)
NO(g)
H2O(g)
192
205
211
189
Calculate the standard entropy change, in J K–1 mol–1, for this oxidation of ammonia.
ΔS –o– = ....................................... J K–1 mol–1 [2]
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ENTROPY WS 1
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17
(d) The exothermic reaction below occurs spontaneously at low temperatures but does not occur
at very high temperatures.
2SO2(g) + O2(g)
2SO3(g)
Explain why.
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
...................................................................................................................................................
.............................................................................................................................................. [2]
(e) An ore of iron contains iron(III) oxide, Fe2O3.
Iron is extracted from this ore by heating with carbon.
The equation below shows one of the reactions which takes place.
Fe2O3(s) + 3C(s)
2Fe(s) + 3CO(g)
ΔS = +543 J K–1 mol–1 and ΔH = +493 kJ mol–1
Calculate the minimum temperature at which this reaction becomes feasible.
Show all your working.
minimum temperature = .......................................................... [3]
[Total: 10]
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ENTROPY WS 1
116
12
55
Chemists use three energy terms, enthalpy, entropy and free energy, to help them make predictions
about whether reactions may take place.
(a) The table below shows five processes. Each process has either an increase in entropy or a
decrease in entropy.
For each process, tick ( ) the appropriate box.
increase in
entropy
process
A
C2H5OH(l)
B
C2H2(g) + 2H2(g)
C
NH4Cl (s) + aq
NH4Cl (aq)
D
4Na(s) + O2(g)
2Na2O(s)
E
2CH3OH(l) + 3O2(g)
decrease in
entropy
C2H5OH(g)
C2H6(g)
2CO2(g) + 4H2O(l)
[2]
(b) At 1 atm (101 kPa) pressure, ice melts into water at 0 °C.
Complete the table below using the symbols ‘+’, ‘–’ or ‘0’ to show the sign of ΔH and ΔS for the
melting of ice at 0 °C and 1 atm.
For each sign, explain your reasoning.
energy
change
sign
+, – or 0
reasoning
ΔH
ΔS
[2]
© OCR 2011
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ENTROPY WS 1
117
13
(c) Much of the hydrogen required by industry is produced by reacting natural gas with steam:
CH4(g) + H2O(g)
3H2(g) + CO(g)
Standard entropies are given in the table below.
substance
S o / J K–1 mol–1
(i)
CH4(g)
H2O(g)
H2(g)
CO(g)
186
189
131
198
Calculate the standard entropy change, in J K–1 mol–1, for this reaction of natural gas
with steam.
ΔS o = ...................................... J K–1 mol–1 [2]
(ii)
State two large-scale uses for the hydrogen produced.
1. ........................................................................................................................................
2. .................................................................................................................................. [1]
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ENTROPY WS 1
118
14
(d) Ammonium chloride, NH4Cl, can dissociate to form ammonia, NH3, and hydrogen chloride,
HCl.
NH4Cl (s)
NH3(g) + HCl (g)
At 298 K, ΔH = +176 kJ mol–1 and ΔG = +91.2 kJ mol–1.
•
•
Calculate ΔG for this reaction at 1000 K.
Hence show whether this reaction takes place spontaneously at 1000 K.
Show all your working.
ΔG = ........................................... kJ mol–1 [4]
[Total: 11]
© OCR 2011
ΔG = ........................................... kJ mol–1 [4]
[Total: 11]
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ENTROPY WS 1
119
14
65
Entropy changes are an important factor in determining the feasibility of reactions.
(a) You are provided with equations for four processes.
A
B
C
D
2SO3(g)
2SO2(g) + O2(g)
H2O(g)
H2O(l)
H2O(l)
H2(g) + ½O2(g)
2CO(g)
2C(s) + O2(g)
For each process, explain why ΔS has the sign shown below.
A: sign of ΔS: negative
reason for sign: .........................................................................................................................
...................................................................................................................................................
B: sign of ΔS: positive
reason for sign: .........................................................................................................................
...................................................................................................................................................
C: sign of ΔS: negative
reason for sign: .........................................................................................................................
...................................................................................................................................................
D: sign of ΔS: positive
reason for sign: .........................................................................................................................
.............................................................................................................................................. [4]
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ENTROPY WS 1
120
15
(b) Calcium oxide, CaO, is used to make cement. Calcium oxide is manufactured by the thermal
decomposition of calcium carbonate.
CaCO3(s)
ΔH = +178 kJ mol–1
CaO(s) + CO2(g)
Standard entropies of CaCO3(s), CaO(s) and CO2(g) are given in the table below.
substance
CaCO3(s)
CaO(s)
CO2(g)
S / J K–1mol–1
89
40
214
•
Using the information in the table, show that the entropy change, ΔS, for the decomposition
of calcium carbonate is 0.165 kJ K–1 mol–1.
•
Show that calcium carbonate is stable at room temperature (25 °C).
•
Calculate the minimum temperature needed to decompose calcium carbonate.
Show all your working.
[7]
[Total: 11]
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ENTROPY WS 1
121
14
7(e) In the industrial production of ammonia, a temperature in the range 400–500 °C is used.
N2(g) + 3H2(g)
2NH3(g)
ΔH = –92 kJ mol–1
Standard entropies of N2(g), H2(g) and NH3(g) are given in the table below.
substance
S / J K–1 mol–1
(i)
N2(g)
H2(g)
NH3(g)
191
131
192
Show that the formation of ammonia from nitrogen and hydrogen gases should be
feasible at room temperature (25 °C).
[6]
(ii)
Explain, in terms of entropy, why this reaction is not feasible at very high temperatures.
...........................................................................................................................................
...........................................................................................................................................
...........................................................................................................................................
...................................................................................................................................... [2]
(iii)
Suggest why a temperature of 400–500 °C is used for ammonia production, despite the
reaction being feasible at room temperature.
...........................................................................................................................................
...................................................................................................................................... [1]
[Total: 22]
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ENTROPY WS 1
122
CEDAR COLLEGE
ENTROPY WS 1
123
ENTROPY WS 2
1
= ............................... kJ mol–1 [3]
(b) Entropy is a measure of the disorder of a system.
Describe and explain what happens to the entropy of a gas when the temperature is increased.
....................................................................................................................................................
....................................................................................................................................................
..............................................................................................................................................
[2]
5
(c) The table shows four reactions.
© UCLES 2016
(i)
9701/42/F/M/16
For each reaction, predict the sign of the entropy change, S o. If you predict no entropy
chan e rite no chan e in the ta le elo
he first one has een one for yo
reaction
CO(g) + O2(g)
1
2
Mg(s) +
O2(g)
CuSO4(s) + 5H2O(l)
NaHCO3(s) + H+(aq)
sign of S o
CO2(g)
negative
MgO(s)
CuSO4.5H5O(s)
Na+(aq) + CO2(g) + H2O(l)
[2]
(ii)
lain hy the entro y chan e for the first rocess is ne ati e
.............................................................................................................................................
....................................................................................................................................... [1]
(d) Calculate the standard entropy change, S o, for this reaction.
N2(g) + 3H2(g)
2NH3(g)
Standard entropies, S o, in J K–1 mol–1 are given.
N2(g)
H2(g)
NH3(g)
+192
+131
+193
S o ............................ J K–1 mol–1 [2]
(e) Whether or not a chemical reaction is spontaneous (feasible) can be deduced by calculating
the change in free energy, G o, at a given temperature.
MgCO3(s)
(i)
MgO(s) + CO2(g)
H o = +117 kJ mol–1
S o = +175 J K–1 mol–1
Calculate the value of G o at 298 K for the above reaction.
[2]
CEDAR COLLEGE
ENTROPY
(ii) Use your answer to (i) to explain whether or not this reaction is spontaneous
at 298 K.WS 2
.............................................................................................................................................
S o ............................ J K–1 mol–1 [2]
124
(e) Whether or not a chemical reaction is spontaneous (feasible) can be deduced by calculating
the change in free energy, G o, at a given temperature.
MgCO3(s)
(i)
MgO(s) + CO2(g)
H o = +117 kJ mol–1
S o = +175 J K–1 mol–1
Calculate the value of G o at 298 K for the above reaction.
[2]
(ii)
Use your answer to (i) to explain whether or not this reaction is spontaneous at 298 K.
.............................................................................................................................................
....................................................................................................................................... [1]
[M’16 2 Q2]
[Total: 16]
5
© UCLES 2016
2
[Turn over
9701/42/F/M/16
(c) (i) Predict the sign of S o for this reaction. Explain your answer.
2H2S(g) + CH4(g)
CS2(g) + 4H2(g)
H o = +241 kJ mol–1
.............................................................................................................................................
....................................................................................................................................... [1]
The free energy change, G o, for this reaction at 1000 K is +51 kJ mol–1.
(ii)
Calculate the value of S o for this reaction, stating its units.
S o = ............................. units ............................. [2]
(d) How would the value of G o, and hence the spontaneity (feasibility) of this reaction change as
the temperature increases? Explain your answer.
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
[Total: 10]
CEDAR COLLEGE
ENTROPY WS 2
125
6
33
The spontaneity (feasibility) of a chemical reaction depends on the standard Gibbs free energy
change, G o. This is related to the standard enthalpy and entropy changes by the equation shown.
Go = Ho – T So
(a) State and explain whether the following processes will lead to an increase or decrease in
entropy.
(i)
the reaction of magnesium with hydrochloric acid
entropy change ...................................................................................................................
(ii)
explanation .........................................................................................................................
[1]
solid potassium chloride dissolving in water
entropy change ...................................................................................................................
(iii)
explanation .........................................................................................................................
[1]
steam condensing to water
entropy change ...................................................................................................................
explanation .........................................................................................................................
[1]
(b) Magnesium carbonate can be decomposed.
MgCO3(s)
s
2
(g)
Ho
mol–1
Standard entropies are shown in the table.
substance
So
(i)
MgCO3(s)
MgO(s)
CO2(g)
mol–1 K–1
Calculate G o for this reaction at 298 K.
Include a relevant sign and give your answer to three si nificant fi
Go
(ii)
Explain, with reference to
temperatures.
res
mol–1 [3]
G o, why this reaction becomes more feasible at higher
.............................................................................................................................................
....................................................................................................................................... [1]
© UCLES 2016
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9701/41/O/N/16
ENTROPY WS 2
126
7
(c) On heating, sodium hydrogencarbonate decomposes into sodium carbonate as shown.
2NaHCO3(s)
Na2CO3 s
2
2
O(g)
Ho
So
mol–1
mol–1 K–1
Calculate the minimum temperature at which this reaction becomes spontaneous (feasible).
Show your working.
temperature = ............................. K [2]
[W’16 1 Q3]
(d) The solubility of Group 2 sulfates decreases down the Group.
Explain this trend.
....................................................................................................................................................
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
[Total: 11]
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ENTROPY WS 2
127
7
4
(c) Iron(III) oxide can be reduced to iron metal using carbon monoxide at a temperature of 1000 C.
Fe2O3(s) + 3CO(g)
2Fe(s) + 3CO2(g)
H o = – 43.6 kJ mol–1
Some relevant standard entropies are given in the table.
(i)
substance
Fe2O3(s)
CO(g)
Fe(s)
CO2(g)
S o / J K–1 mol–1
+90
+198
+27
+214
What is meant by the term entropy ?
.............................................................................................................................................
....................................................................................................................................... [1]
(ii)
Calculate the standard entropy change, S o, for this reaction.
S o = ............................. J K–1 mol–1 [2]
(iii)
Calculate the standard Gibbs free energy change, G o, for this reaction at 25 C.
G o = ............................. kJ mol–1 [2]
(iv)
Suggest why a temperature of 1000 C is usually used for this reaction, even though the
reaction is spontaneous (feasible) at 25 C. Explain your answer.
.............................................................................................................................................
.............................................................................................................................................
....................................................................................................................................... [1]
[W’16 2 Q3]
[Total: 13]
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9701/42/O/N/16
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ENTROPY WS 2
128
5
5
(c) Chlorine is in Group 17.
uggest the trend in the first electron affinity of the ele ents in
roup
plain your answer
....................................................................................................................................................
....................................................................................................................................................
.............................................................................................................................................. [2]
(d) The equation for the formation of magnesium oxide from its elements is shown.
1
2 O2(g)
Mg(s) +
substance
Mg(s)
O2(g)
MgO(s)
MgO(s)
ΔH o = – 602 kJ mol–1
S o / J K–1 mol–1
32.7
205
26.9
Use the equation and the data given in the table to calculate ΔG o for the reaction at 25 C.
ΔG o = .............................. units ..............................
[4]
[M’17 2 Q2]
[Total: 10]
© UCLES 2017
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9701/42/F/M/17
[Turn over
ENTROPY WS 2
129
12
12
12
7 67(a) (a)
(i) Complete
thethe
equations
to to
show
the
two
types
repeat
unit for
for
Complete
equations
show
the
two
typesof
ofpolymerisation.
polymerisation.Draw
Draw one
one repeat
repeat unit
unit
7 (a) (i)(i) Complete
the equations
to show
the
two
types
of
polymerisation.
Draw
one
for
each
polymer.
Include
any
other
products.
eachpolymer.
polymer.Include
Includeany
anyother
otherproducts.
products.
each
addition
poly
addition
polyerisation
erisation
addition
poly
erisation
CH=CHCH
n CH
2=CHCH
3(g)
2=CHCH
3(g)
n nCH
(g)
2
3
condensation polyerisation
erisation
condensation
condensationpoly
poly erisation
n HO2CCH2CO2H(s)
n HO
n HO
2CCH
2CO
2H(s)
2CCH
2CO
2H(s)
+
+ +
n HOCH2CH2OH(l)
n HOCH
n HOCH
2CH
2OH(l)
2CH
2OH(l)
[3]
[3]
[3]
o
(ii) Suggest the sign of the entropy changes, ΔSo , for each of the two types of polymerisation.
foreach
eachof
of the
the two
two types
types of
Suggest
the
signofofthe
theentropy
entropychanges,
changes,ΔS
ΔSo, ,for
of polymerisation.
polymerisation.
(ii)(ii) Suggest
the
sign
Explain
your
answers.
Explain
your
answers.
Explain your answers.
ΔSo o for addition polymerisation
additionpolymerisation
polymerisation
o
forfor
addition
ΔSΔS
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
ΔSo o for condensation polymerisation
for condensation polymerisation
ΔS
ΔS o for condensation polymerisation
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
[2]
.............................................................................................................................................
[2]
[2]
© UCLES 2018
© UCLES 2018
© UCLES 2018
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9701/42/F/M/18
9701/42/F/M/18
ENTROPY WS 2
130
13
13
13
(b) An amide bond forms when a carboxylic acid reacts with an amine.
(b)
(b) An
An amide
amide bond
bond forms
forms when
when aa carboxylic
carboxylic acid
acid reacts
reacts with
with an
an amine.
amine.
(i) Complete the equation by writing the products in the box.
(i)
(i) Complete
Complete the
the equation
equation by
by writing
writing the
the products
products in
in the
the box.
box.
R–CO2H + H2N–R'
R–CO
R–CO22HH ++ HH22N–R'
N–R'
(ii)
(ii)
(ii)
(iii)
(iii)
(iii)
+
++
[1]
[1]
Use your answer to (i) to work out the bonds that are broken and the bonds that are
Use
your
answer
bonds
and
formed
during
the to
reaction
between
carboxylic
acidare
andbroken
an amine.
Use
your
answer
to (i)
(i) to
to work
work out
out athe
the
bonds that
that
are
broken
and the
the bonds
bonds that are
formed
formed during
during the
the reaction
reaction between
between aa carboxylic
carboxylic acid
acid and
and an
an amine.
amine.
bonds that are broken
bonds
bonds that
that are
are broken
broken
.............................................................................................................................................
.............................................................................................................................................
.............................................................................................................................................
bonds that are formed
bonds that
that are
are formed
formed
bonds
.............................................................................................................................................
[2]
.............................................................................................................................................
.............................................................................................................................................
[2]
Use bond energy values from the Data Booklet to calculate the enthalpy change, ΔH o,
when
one energy
mole
ofvalues
amide from
bonds
is formed
in the reaction
in (i).the
Use
bond
energy
values
from the
the
Data Booklet
Booklet
to calculate
calculate
the enthalpy
enthalpy change,
change, ΔH oo,
Use
bond
Data
to
when one
one mole
mole of
of amide
amide bonds
bonds is
is formed
formed in
in the
the reaction
reaction in
in (i).
(i).
when
ΔH o = .............................. kJ [2]
.............................. kJ [2]
ΔHoo == ..............................
ΔH
(c) Amide bonds can also be formed by reacting acyl chlorides with amines.
(c) Amide
Amide bonds
bonds can
can also
also be
be formed
formed by
by reacting
reacting acyl
acyl chlorides
chlorides with
with amines.
amines.
(c)
The enthalpy change for this process, ΔH o, is – 6.00 kJ mol–1.
–1
is ––6.00
6.00kJ
kJmol
mol–1
The enthalpy
enthalpy change
change for
for this
this process,
process, ΔH
ΔHoo,, is
..
The
Calculate the minimum entropy change, ΔS o, for this reaction to be spontaneous (feasible) at
298 K.
for this
this reaction
reaction to
to be
be spontaneous
spontaneous (feasible)
(feasible) at
Calculate
the minimum
minimum entropy
entropy change,
change, ΔS
ΔSoo,, for
Calculate
the
298
K.
298 K.
ΔS o = .............................. J K–1 mol–1 [2]
–1
–1
.............................. JJK
K–1
mol–1
[2]
ΔSoo == ..............................
mol
[2]
ΔS
[M’17 2 Q1]
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CEDAR COLLEGE
ENTROPY WS 2