School of Chemistry KRA113 Thermodynamics Questions – Thermochemistry Dr Stuart Thickett Question 1. Identify the following systems as open, closed or isolated: (a) a space shuttle rocket booster; (b) hot coffee in a perfectly insulated pot. Question 2. A piece of silver of mass 363 g has a heat capacity of 85.7 JoC-1. What is the specific heat capacity of the silver? Question 3. Burning a 1.500 g sample of methane, CH4, in a bomb calorimeter increases the temperature of the calorimeter by 2.190 oC. The enthalpy of combustion of methane is − 890.3 kJ mol-1. Calculate the heat capacity of the calorimeter in kJ/oC. Question 4. When 2.266 g of an unknown compound is burned in the same calorimeter, the temperature of the calorimeter increases by 1.059 oC. Calculate the heat of combustion of the unknown compound in kJ g-1. Question 5. A piece of Cu of mass 19.0 g at 87.4 °C was placed in a calorimeter containing 55.5 g of water at 18.3 °C. The final temperature was 20.4 °C. Calculate the specific heat capacity of the Cu. Question 6. Consider the reaction, 2 CH3OH(l) + 3 O2(g) → 4 H2O(l) + 2 CO2(g) .......... ΔH = -1452.8 kJ. What is the value of ΔH if: (i). (ii). (iii). Question 7. The equation is multiplied throughout by 2? The direction of the reaction is reversed so that the products become the reactants and vice versa? Water vapour instead of liquid water is formed as a product? (Provide a qualitative answer only, will ΔH increase or decrease?) Define Hess’s Law and the standard enthalpy of formation Question 8 . Nitromethane, CH3NO2, is a good fuel. It is a liquid at room temperature. When the liquid is burned, the reaction involved is: 2 CH3NO2(l) + 1½ O2(g) → 2 CO2(g) + N2(g) + 3 H2O(l) The standard enthalpy of formation of liquid nitromethane at 25 oC is -112 kJ mol-1. Using the following information: (i) the enthalpy of formation of CO2(g) is -393.5 kJ mol-1 (ii) the enthalpy of formation of H2O(l) is -285.8 kJ mol-1 Calculate the enthalpy change in the burning of 5 moles of liquid nitromethane to form products at 25 oC. Comment on the magnitude of the result obtained and state whether the reaction is exothermic or endothermic.