Question

Work Session: Thermochemistry 1. Ethanol is added to gasoline because the oxygen it contains improves gasoline's burning efficiency. Its combustion reaction is given below. CHsCH2OH(I) + 3O2(g) → 2CO2(g) + 3H20(g) aH--1 236 kJ a) Is this an exothermic or endothermic reaction? b) If 15.3 grams of pure ethanol is completely converted to products, calculate how much heat is absorbed or released, in (1) kJ and in (2) kcal. c) If 42.7 g of water vapor is produced, how much heat, in kJ, is absorbed or released? 2. Ammonium nitrate was the oxidizing agent used that damaged the New York World Trade Center in 1993 and the Federal Building in Oklahaoma City in 1995. The thermochemical equation for its decomposition is given below. What quantity of heat is evolved from the decomposition of 50.0 kg of ammonium nitrate? NH4NO (s) .N.O(g) 2H20(g) AH-82 1 kJ

Answer 1

CH_3 CH_2 OH + 3O_2 rightarrow 2CO_2 + 3H_2O Delta H = -1236 KJ (a) because 46 gm CH_3 CH_2 OH is releasing 1236 KJ of energy. So the reaction is Exothermic Reaction. (b) because 46 gm CH_3 CH_2 OH = 1236 KJ so 15.3 gm CH_3 CH_2 OH = 1236/46 times 15.3 KJ = 411.10 KJ released because 1 KJ = 0.239 Kcal So = 411.10 times 0.239 kcal = 98.2529 Kcal released (c) because 54 gm H_2O produced = 1236 KJ so 42.7 gm H_2O produced = 1236/54 times 42.7 KJ = 977.35 KJ released NH_4 NO_3 rightarrow N_2O + 2 H_2O Delta H = -82.1 KJ because 80 Kg NH_4 NO_3 = 82.1 KJ So 50 Kg NH_4 NO_3 = 82.1/80 times 50 KJ = 51.3125 KJ