1.
When hydrogen peroxide decomposes, the temperature of the reaction mixture increases.
2H2O2(aq) → O2(g) + 2H2O(l)
What are the signs of ∆H, ∆S and ∆G for this reaction?
∆H
∆S
∆G
A.
–
–
–
B.
–
+
–
C.
+
+
–
D.
–
+
+
(Total 1 mark)
2.
Which change will not increase the entropy of a system?
A.
Increasing the temperature
B.
Changing the state from liquid to gas
C.
Mixing different types of particles
D.
A reaction where four moles of gaseous reactants changes to two moles of gaseous
products
(Total 1 mark)
3.
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.
................................................................................................................................................
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(Total 1 mark)
IB Questionbank Chemistry
1
4.
Consider the following Born-Haber cycle:
The magnitudes for each of the enthalpy changes (a to e) are given in kJ mol–1 but their signs
(+ or –) have been omitted.
(i)
State the names for the enthalpy changes c and d.
(2)
(ii)
Deduce which two of the enthalpy changes a to e have negative signs.
(1)
(iii)
Determine the value for the enthalpy of formation of potassium bromide.
(2)
(iv)
Explain why the quantitative value for the lattice enthalpy of calcium bromide is larger
than the value for the lattice enthalpy of potassium bromide.
(2)
(Total 7 marks)
IB Questionbank Chemistry
2
5.
Which reaction has the largest increase in entropy?
A.
H2(g) + Cl2(g) → 2HCl(g)
B.
Al(OH)3(s) + NaOH(aq) → Al(OH)4–(aq) + Na+(aq)
C.
Na2CO3(s) + 2HCl(aq) → 2NaCl(aq) + CO2(g) + H2O(l)
D.
BaCl2(aq) + Na2SO4(aq) → BaSO4(s) + 2NaCl(aq)
(Total 1 mark)
6.
Consider the following reaction.
2CH3OH(g) + H2(g) → C2H6(g) + 2H2O(g)
(a)
The standard enthalpy change of formation for CH3OH(g) at 298 K is –201 kJ mol–1 and
for H2O(g) is –242 kJ mol–1. Using information from Table 11 of the Data Booklet,
determine the enthalpy change for this reaction.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)
(b)
The standard entropy for CH3OH(g) at 298 K is 238 J K–1 mol–1, for H2(g) is
131 J K–1 mol–1 and for H2O(g) is 189 J K–1 mol–1. Using information from Table 11 of
the Data Booklet, determine the entropy change for this reaction.
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
......................................................................................................................................
(2)
IB Questionbank Chemistry
3
(c)
Calculate the standard change in free energy, at 298 K, for the reaction and deduce
whether the reaction is spontaneous or non-spontaneous.
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......................................................................................................................................
(3)
(Total 7 marks)
7.
Which is a correct definition of lattice enthalpy?
A.
It is the enthalpy change that occurs when an electron is removed from 1 mol of gaseous
atoms.
B.
It is the enthalpy change that occurs when 1 mol of a compound is formed from its
elements.
C.
It is the enthalpy change that occurs when 1 mol of solid crystal changes into a liquid.
D.
It is the enthalpy change that occurs when 1 mol of solid crystal is formed from its
gaseous ions.
(Total 1 mark)
8.
Consider the following reaction:
N2(g) + 3H2(g)
(i)
2NH3(g)
Suggest why this reaction is important for humanity.
(1)
(ii)
Using the average bond enthalpy values in Table 10 of the Data Booklet, calculate the
standard enthalpy change for this reaction.
(4)
IB Questionbank Chemistry
4
(iii)
The absolute entropy values, S, at 238 K for N2(g), H2(g) and NH3(g) are 192, 131 and
193 J K–1 mol–1 respectively. Calculate ∆Sο for the reaction and explain the sign of ∆Sο.
(2)
(iv)
Calculate ∆Gο for the reaction at 238 K. State and explain whether the reaction is
spontaneous.
(3)
(v)
If ammonia was produced as a liquid and not as a gas, state and explain the effect this
would have on the value of ∆Hο for the reaction.
(2)
(Total 12 marks)
9.
Which ionic compound has the most endothermic lattice enthalpy?
A.
NaCl
B.
KCl
C.
NaF
D.
KF
(Total 1 mark)
IB Questionbank Chemistry
5