JPJC 2026 Chemical Energetics Revision

2026 JPJC JC1 H2 Chemistry (9476) 1 Topic 5: Chemical Energetics JURONG PIONEER JUNIOR COLLEGE Topical Revision for Physical Chemistry (Topic 5: Chemical Energetics) FOUNDATION KIT 1 [PJC MYE 2011/P1/Q13] When 25 cm 3 of 1.0 mol dm –3 NaOH(aq) is completely neutralised by 1.0 mol dm –3 HCl(aq), the temperature of the mixture rose by 6.8 oC. What will be the temperature change if 50 cm 3 of 0.5 mol dm –3 NaOH(aq) is completely neutralised by 0.5 mol dm–3 HCl(aq)? [Assume heat loss to be negligible in each case . Given that the specific heat capacity of the resulting solution is 4. 18 J g–1 K–1 and the density of the resulting solution is 1 g cm–3.] A 1.7 oC B 3.4 oC C 6.8 oC D 13.6 oC 2 [PJC Promo 2011/P1/Q12] In an experiment, 4.2 g of sodium fluoride was dissolved in 200 cm 3 of water which was at an initial temperature of 25.0 °C. Given the enthalpy change of solution of sodium fluoride is +71 kJ mol –1, what would be the final temperature of the solution when the sample of sodium fluoride dissolved completely? (Assume that the specific heat capacity of the solution is 4.2 J cm–3 K–1.) A 16.5 oC B 24.5 oC C 25.5 oC D 33.5 oC 3 [PJC Promo 2013/P1/Q11] Which of the following has the same value as the standard enthalpy change of formation of carbon monoxide? [Hc and Hf represent the standard ent halpy change of combustion and formation respectively] A ½Hc(C(graphite)) B Hf(CO2) – Hc(C(graphite)) C Hf(CO2 ) – ½ Hc(C(graphite)) D Hc(C(graphite)) – Hc(CO)

2026 JPJC JC1 H2 Chemistry (9476) 2 Topic 5: Chemical Energetics 4 [PJC Promo 2012/P1/Q8] Some enthalpy changes are given below. Hc(C) = –394 kJ mol–1 Hf(H2O) = –286 kJ mol–1 Hf(CH3OH) = –239 kJ mol–1 What is the enthalpy change of combustion of methanol, CH3OH? A –441 kJ mol–1 B –727 kJ mol–1 C +441 kJ mol–1 D +727 kJ mol–1 5 [PJC MYE 2010/P1/Q14] In oil refineries, an important process is the recovery of any sulfur from petroleum. Sulfur compounds are converted into the gas hydrogen sulfide, H 2S, by using a catalyst. The H2S is then oxidised by using a controlled amount of air to give steam, H 2O(g), and sulfur, S(s). The enthalpy change of formation of H 2S(g) is –20.5 kJ mol –1 and that of H 2O(g) is –243.0 kJ mol–1. What is the enthalpy change of reaction per mole of H2S? A –202.5 kJ mol–1 B –222.5 kJ mol–1 C –263.5 kJ mol–1 D –445.0 kJ mol–1 6 [AJC Promo 2016/P1/Q20] Use of the Data Booklet is relevant to this question. Dinitrogen oxide, N=N=O, burns in gaseous ethyne, H–CC–H, to produce water vapour, carbon dioxide and nitrogen gases as the only products. 5N2O(g) + C2H2(g) → H2O(g) + 2CO2(g) + 5N2(g) Given that the enthalpy change of the reaction is –1668 kJ mol –1 and the nitrogen–nitrogen bond energy in dinitrogen oxide is +418 kJ mol –1, what is the nitrogen–oxygen bond energy in dinitrogen oxide? A +382 kJ mol–1 B +594 kJ mol–1 C +688 kJ mol–1 D +1350 kJ mol–1

2026 JPJC JC1 H2 Chemistry (9476) 3 Topic 5: Chemical Energetics 7 [PJC MYE 2011/P1/Q20] Calcium reacts with water to form calcium hydroxide and hydrogen. Ca(s) + 2H2O(l) → Ca(OH)2(s) + H2(g) The standard enthalpy change for this reaction can be measured in the laboratory. What further information is needed in order to calculate the standard enthalpy change of formation of calcium hydroxide, ∆Hf (Ca(OH)2(s))? 1 ∆Hf (H2O(l)) 2 ∆Hf (H2(g)) 3 first and second ionisation energies of Ca A 1, 2 and 3 are correct B 1 and 2 are correct C 2 and 3 are correct D 1 only is correct 8 [PJC Promo 2011/P1/Q27] The enthalpy level diagram shown represents the dissolving of anhydrous magnesium chloride in a large volume of water. Which statements about the process are correct? 1 The lattice energy of magnesium chloride is –2526 kJ mol–1. 2 The enthalpy change of hydration of the chloride ion is –384 kJ mol–1. 3 The enthalpy change of solution of anhydrous magnesium chloride is –132 kJ mol-1. A 1, 2 and 3 are correct B 1 and 2 are correct C 1 only is correct D 2 only is correct MgCl2(aq) MgCl2(s) –1890 + 2(–384) kJ mol–1 +2526 kJ mol–1 enthalpy Mg2+(g) + 2Cl – (g)

2026 JPJC JC1 H2 Chemistry (9476) 4 Topic 5: Chemical Energetics 9 [AJC Promo 2016/P1/Q21] Which enthalpy change could always be correctly represented by the enthalpy diagram shown? 1 solution 2 hydration 3 neutralisation A 1 and 2 are correct B 2 and 3 are correct C 2 only is correct D 3 only is correct 10 [PJC Promo 2013/P1/Q28] Which of the following information would not be required to estimate the lattice energy of the hypothetical ionic compound, CaF3? 1 The calcium-fluorine bond energy 2 The third electron affinity of fluorine 3 The third ionisation energy of fluorine A 1, 2 and 3 are correct B 1 and 2 are correct C 1 and 3 are correct D 2 and 3 are correct H products reactants reaction pathway enthalpy (H)

2026 JPJC JC1 H2 Chemistry (9476) 5 Topic 5: Chemical Energetics 11 [PJC MYE 2012/P1/Q20] The standard enthalpy changes of combustion of phosphorus in different allotropic forms are as follows: P(red) = –2941 kJ mol–1 P(white) = –2971 kJ mol–1 P(black) = –2925 kJ mol–1 Which of the following deductions can be made from the data above? 1 P(red) has a higher energy content than P(black). 2 The stability of phosphorus allotropes decreases in the order: P(black) > P(red) > P(white). 3 P(white) is formed exothermically from P(black). A 1, 2 and 3 are correct B 1 and 2 are correct C 1 and 3 are correct D 2 and 3 are correct 12 [JPJC Promo 2020/P1/Q14] The conversion of graphite into diamond is an endothermic reaction. C(graphite) → C(diamond) H > 0 Which statements are correct? 1 Graphite is more energetically stable than diamond. 2 The enthalpy change of combustion of diamond is more exothermic than that of graphite. 3 The enthalpy change of atomisation of diamond is less endothermic than that of graphite. A 1, 2 and 3 B 1 and 2 only C 1 and 3 only D 2 and 3 only 13 [PJC MYE 2011/P1/Q15] When ice melts, 6.0 kJ mol –1 of heat enthalpy is absorbed. What is the entropy change when 54 g of ice melts at 0 oC? A –66 J K–1 B –22 J K–1 C +22 J K–1 D +66 J K–1

2026 JPJC JC1 H2 Chemistry (9476) 6 Topic 5: Chemical Energetics 14 [JPJC Promo 2019/P1/Q10] Liquid G has an H of vapourisation of +10.0 kJ mol–1 and a boiling point of 266 K. What is the S of condensation of vapour G? A –1430 J mol–1 K–1 B –37.6 J mol–1 K–1 C +1430 J mol–1 K–1 D +37.6 J mol–1 K–1 15 In the military, self -heating ready-to-eat (RTE) meals allow soldiers in the battlefield to prepare hot meals easily and quickly without the need for a visible flame. These RTE meals contain food in a double -walled container with finely powdered magnesium in a packet and water between the walls. Upon opening a RTE meal, the packet breaks, allowing the magnesium powder to react with water to warm up the food. Mg(s) + 2H2O(l) → Mg(OH)2(s) + H2(g) What are the signs of ∆H, ∆S and ∆G for the overall process? H S G A + + – B + + + C – – – D – + – 16 Which one of the following equations represents a r eaction that is feasible at all temperatures? A CaCO3(s) → CaO(s) + CO(g) ∆H > 0 B 4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(l) ∆H < 0 C 3C(s) + 2H2(g) → C3H4(g) ∆H > 0 D 5N2O(g) + C2H2(g) → H2O(g) + 2CO2(g) + 5N2(g) ∆H < 0

2026 JPJC JC1 H2 Chemistry (9476) 7 Topic 5: Chemical Energetics 17 [PJC MYE 2011/P2/Q2(a)] Calcium oxide is a white, alkaline crystalline solid at room temperature. It is an inexpensive material u