NJC H1 Chemical Energetics Tutorial

National Junior College SH1 H1 Chemistry 1 Chemical Energetics Tutorial 1 Write thermochemical equations to represent the following statements: (a) Standard enthalpy change of formation of hydrogen bromide gas is –36.2 kJ mol−1 (b) Standard enthalpy change of combustion of liquid propanol (CH3CH2CH2OH) is – 2017 kJ mol−1 (c) Standard enthalpy change of neutralisation of hydrochloric acid and sodium hydroxide is −57 kJ mol−1 (d) Lattice energy of calcium chloride solid is –2237 kJ mol−1 (e) Bond energy of I−I (refer to the Data Booklet for the bond energy) 2 [N2008 P1 Q32] Which reactions represent standard enthalpy changes? 1 NH3(g) + HCl(g) → NH4Cl(s) 2 C(g) + 6H(g) → C2H6(g) 3 CH4(g) + 2O2(g) → CO2(g) + 2H2O(g) A 1 only B 1 and 2 only C 2 and 3 only D 1, 2 and 3 3 The heat liberated in the neutralisation given below is −114 kJ mol−1. 2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) By using this information, what is the most likely value for the heat liberated in the following neutralisation? Ba(OH)2(aq) + 2HCl(aq) → BaCl2(aq) + 2H2O(l) A −57 kJ mol−1 B −76 kJ mol−1 C −114 kJ mol−1 D −228 kJ mol−1 4 The enthalpy change of neutralisation of ethanoic acid with sodium hydroxide can be found experimentally by mixing known volumes of 1.0 mol dm –3 ethanoic acid, CH 3COOH, and 1.0 mol dm–3 NaOH. The following results are obtained. Volume of CH3COOH used = 40.0 cm3 Volume of NaOH used = 30.0 cm3 Initial temperature of mixture = 28.0 C Final temperature of mixture = 32.6 C (a) Use the data given to calculate the standard enthalpy change of neutralisation of CH3COOH with NaOH. [–44.9 kJ mol–1] (b) The experiment is repeated with NaOH and HCl and it is found that the enthalpy change of reaction between NaOH and HC l is more exothermic than that calculated in (a). Explain why this is so.

National Junior College SH1 H1 Chemistry 2 5 When 1.00 g of ethanol in a spirit lamp was burned under a container of water, it was found that 100 cm 3 of water was heated from 15 C to 65 C. The process was known to be only 70% efficient. (a) Suggest reasons why only 70% of heat released by combustion is transferred to the water. (b) Calculate the standard enthalpy change of combustion of ethanol. [–1370 kJ mol–1] (c) By using the value you have obtained in (b) and the following data: Enthalpy change of combustion of carbon −393.5 kJ mol−1 Enthalpy change of combustion of hydrogen −285.8 kJ mol−1 Calculate the enthalpy change of formation of ethanol. 2 C(s) + 3 H2(g) + ½ O2 (g) ⎯→ CH3CH2OH(l) ∆Hf =? [–271 kJ mol–1] 6 When 6 g each of carbon, hydrogen and methanol, CH 3OH (l), are completely burnt in oxygen, 196.8, 857.7 and 136.2 kJ of heat are evolved respectively. Calculate the enthalpy change of f