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Topic 15: Energetics/Thermochemistry
For HL students only
1. [1 mark]
Which magnitudes of lattice enthalpy and hydration enthalpy of ions for an ionic substance would result in the most exothermic enthalpy of solution?
2. [1 mark]
Which alkane has the lowest standard entropy, S⦵?
A. CH4 (g)
B. C2H6 (g)
C. C3H8 (g)
D. C4H10 (g)
3. [1 mark]
At which temperature could ΔH, ΔS, and ΔG all be positive?
A. High temperatures
A. High temperatures
B. Low temperatures
C. Any temperature
D. No temperature
4. [1 mark]
Which compound has the largest value of lattice enthalpy?
A. Na2O
B. K2O
C. Na2S
D. K2S
5. [1 mark]
In which reaction does entropy decrease?
A. NaCl (s) → NaCl (aq)
B. Zn (s) + H2SO4 (aq) → ZnSO4 (aq) + H2 (g)
C. NH3 (g) + HCl (g) → NH4Cl (s)
D. CuCO3 (s) → CuO (s) + CO2 (g)
6. [1 mark]
Which equation represents hydration enthalpy?
A. Na+ (g) → Na+ (aq)
B. Na+ (aq) → Na+ (g)
C. NaCl (s) → NaCl (aq)
D. NaCl (aq) → NaCl (s)
7. [1 mark]
What are the signs of ΔH and ΔS for a reaction that is non-spontaneous at low temperatures but spontaneous at high temperatures?
8. [1 mark]
Which term in the expression ΔG⦵ = ΔH⦵ − TΔS⦵ is an indirect measure of the entropy change of the surroundings when divided by T?
A. ΔG⦵
B. ΔH⦵
C. ΔS⦵
D. −TΔS⦵
9. [1 mark]
Consider the Born–Haber cycle for the formation of sodium oxide:
What is the lattice enthalpy, in kJ mol−1, of sodium oxide?
A. 414 + 2(108) + 249 + 2(496) − 141 + 790
B. 414 + 2(108) + 249 + 2(496) + 141 + 790
C. −414 + 2(108) + 249 + 2(496) − 141 + 790
D. −414 − 2(108) − 249 − 2(496) + 141 − 790
10. [1 mark]
In which of the following situations is the forward reaction spontaneous?
A. The equilibrium constant is greater than one under standard conditions.
B. The cell potential is negative.
C. The Gibbs free energy change of the reverse reaction is negative.
D. The entropy change of the universe for the forward reaction is negative.
11. [1 mark]
The table shows the variation of standard Gibbs energy with temperature for a reversible reaction.
G=H-TS
G=-RT ln K
What can be concluded about the reaction?
A. Equilibrium shifts left as temperature increases.
B. The forward reaction is more spontaneous below 300 K.
C. Entropy is higher in the products than in the reactants.
D. Kc decreases as temperature increases.
12. [1 mark]
Which substance has the highest lattice enthalpy?
A. KCl
B. CaCl2
C. KF
D. CaF2
13. [1 mark]
Which represents electron affinity?
A. Al2+ (g) → Al3+ (g) + e−
B. C (g) + e− → C− (g)
C. Cl2 (g) → 2Cl (g)
D. S (s) → S+ (g) + e−
14. [1 mark]
Which change results in the largest negative value of ΔS?
A. C2H5OH (l) + SOCl2 (l) → C2H5Cl (l) + SO2 (g) + HCl (g)
B. CaCO3 (s) → CaO (s) + CO2 (g)
C. H2O (l) → H2O (s)
D. NH3 (g) + HCl (g) → NH4Cl (s)
15. [1 mark]
Which combination gives the standard hydration enthalpy of Na+ (g)?
A. 4+359+790
B. 4+359-790
C. -4-359+790
D. 4-359+790
16. [1 mark]
Which reaction becomes more spontaneous as temperature increases?
A. CaCO3 s→CaO s+CO2 g
A. CaCO3 s→CaO s+CO2 g
B. N2 g+3H2 g⇌2NH3 g
C. 3CO2 g+4H2O g→C3H8 g+5O2 g
D. SO2 g+H2O2 l→H2SO4 l
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page