IBHL Energetics Review
1. H2O (s)  H2O (l)
When ice melts at its normal melting point, 273.16 K and 1 atmosphere, which of the following is true for the process
shown above?
A.
∆H < 0, ∆S > 0, ∆G > 0
C.
∆H > 0, ∆S > 0, ∆G < 0
B.
∆H > 0, ∆S < 0, ∆G < 0
D.
∆H < 0, ∆S < 0, ∆G > 0
2. Which statement about bonding is correct?
A.
B.
C.
D.
Bond breaking is endothermic and requires energy.
Bond breaking is endothermic and releases energy.
Bond making is exothermic and requires energy.
Bond making is endothermic and releases energy.
3. ∆G calculations predict that a reaction is always spontaneous for which of the following combinations of ∆H
and ∆S?
A.
B.
+∆H and +∆S
+∆H and –∆S
C.
D.
4. Consider the following reactions.
1
Cu2O(s) + O2(g) → 2CuO(s)
2
Cu2O(s) → Cu(s) + CuO(s)
What is the value of ∆H, in kJ, for this reaction?
Cu(s) +
A.
B.
–144 + 11
+144 – 11
–∆H and –∆S
–∆H and +∆S
∆H = –144 kJ
∆H = +11 kJ
1
O2(g) → CuO(s)
2
C.
D.
–144 – 11
+144 + 11
5. Which reaction has the greatest increase in entropy?
A.
SO2(g) + 2H2S(g) → 2H2O(l) + 3S(s)
B.
CaO(s) + CO2(g) → CaCO3(s)
C.
CaC2(s) + 2H2O(l) → Ca(OH)2(s) + C2H2(g)
D.
N2(g) + O2(g) → 2NO(g)
6. Some words used in chemistry can have a specific meaning which is different to their meaning in everyday
English. State what the term spontaneous means when used in a chemistry context.
7. Propane can be formed by the hydrogenation of propene.
CH3CH=CH2(g) + H2(g) → CH3CH2CH3(g)
(i)
State the conditions necessary for the hydrogenation reaction to occur.
(ii)
Enthalpy changes can be determined using average bond enthalpies. Define the term average bond enthalpy.
(2)
(2)
(iii)
Determine a value for the hydrogenation of propene using information from Table 10 of the Data Booklet.
(2)
(iv)
Explain why the enthalpy of hydrogenation of propene is an exothermic process.
(v)
Draw an enthalpy level diagram for the reaction (label: reactants, products, and ∆H) and fill in the blanks:
(1)
[3]
reaction endothermic or exothermic?
________________________
more stable, reactants or products?
________________________
stronger, bonds broken or bonds formed?
________________________
8. Write the formation equation for Na2O(s).
[2]
9. Consider the ionic compound lithium chloride (s).
a) Write an equation that represents the lattice enthalpy for the compound
[1]
b) A Born-Haber cycle for this compound is illustrated below. The relevant enthalpy changes for each
component in the cycle are also given below. Fill in the blanks, labeled a – e, with the appropriate enthalpy
change values given.
[2]
Li(s)  Li(g)
ΔH = +160.7
kJ/mol
Li(g)  Li+ + e-(g)
ΔH = +519
kJ/mol
Cl – Cl
∆H(bond) = +242
kJ/mol
Cl(g) + e-  Cl-(g)
ΔH = -349
kJ/mol
Li(s) + ½ Cl2(g)  LiCl(s) ΔH = - 408.7
kJ/mol
c) Use the values given to determine the lattice enthalpy for lithium chloride (labeled “f” on the diagram).
[2]
d) Match each transition, a – e, with the appropriate process:
[2.5]
i)
formation enthalpy for lithium chloride
_____ a
ii)
ionization energy for lithium
_____ b
iii)
bond enthalpy for chlorine
_____ c
iv)
electron affinity for chlorine
_____ d
v)
enthalpy of vaporization for lithium
_____ e
e) Would you expect the value for ∆Hlat for BeO to be higher or lower than ∆Hlat for lithium chloride?
Explain.
[2]
10. Methanol is made in large quantities as it is used in the production of polymers and fuels. The enthalpy of
combustion of methanol can be determined theoretically or experimentally.
2CH3OH(l) + 3O2(g)  2CO2(g) + 4H2O(g)
a. The enthalpy of combustion of methanol can also be determined experimentally in a school laboratory. A
burner containing methanol was weighed and used to heat water in a test tube as illustrated below.
The following data were collected.
Initial mass of burner and methanol /
g
Final mass of burner and methanol /
g
Mass of water in test tube / g
80.557
Initial temperature of water / °C
21.5
Final temperature of water / °C
26.4
ii. Calculate the amount, in grams, of methanol burned.
80.034
20.000
[1]
iii. Calculate the amount, in mol, of methanol burned.
[1]
iv. Calculate the heat, in kJ, absorbed by the water.
[1]
v. State the heat released, in kJ, released by the reaction.
vi. Determine the enthalpy change, in kJ/mol, for the combustion of methanol.
[1]
[1]
b. The data booklet value for the enthalpy of combustion for methanol is –726 kJ/mol. Suggest why this value
differs from the value calculated in part (a).
[1]
11. Consider the reaction: 2Fe2O3 (s) + 3C(s)  4Fe (s) + 3CO2 (g)
Substance
Fe2O3 (s)
C(s)
Fe (s)
CO2 (g)
∆Hf in kJ/mol
-824
-394
S in J/K*mol
87.4
5.7
27.8
213.7
a) Determine ∆H for the reaction.
[2]
b) Determine ∆S for the reaction.
[2]
c) Determine ∆G for the reaction at 25oC.
[2]
d) Is the reaction spontaneous at 25oC? Explain.
[2]
e) At What temperature will the reaction be at equilibrium?
[2]
12. Calculate the enthalpy of solution for strontium chloride.