Energetics Past Paper Questions

May 2009 Paper 1 Question 3a

Ethene is produced from ethane according to the reaction:

$C_2H_6_{(g)}\rightleftharpoons C_2H_4_{(g)}+H_2_{(g)} \; \; \; \; \; \; \; \; \Delta H=138kJ\: mol^{-1}$

a) The standard enthalpy change of formation of ethane is $-84.7kJ mole^{-1}$ . Determine the standard enthalpy change of formation of ethene. (3 marks)

May 2009 Paper 2 Question 1a

Liquified Petroleum Gas (LPG) is a mixture and butane under a pressure of over 20atm that is used as a domestic and industrial fuel. The enthalpy changes of combustion of the hydrocarbons in LPG are listed in the table below.

	Enthalpy change of combustion
Propane	-50.45 MJ/kg
Butane	-49.62 MJ/kg

a) The enthalpy change of combustion of a sample of LPG was found to be -50.05 MJ kg^-1. Determine the composition of the LPG in terms of mole fractions. (6 marks)

Sept 2009 Paper 1 Question 3a,b,c)

a) Calculate $\Delta H$ for the reaction below in kJ:

$CS_2_{(g)}+3O_2{(g)}\rightleftharpoons CO_2_{(g)}+2SO_2_{(g)}$

given the following enthalpy changes of formation:

$\Delta H_f / kJ mol^{-1}$ : CS₂(g) 110; CO₂(g) -390; SO₂(g) -290. (2 marks)

b) Calculate the enthalpy change when 0.125 moles of CS₂ is burnt in excess oxygen. (2 marks)

c) Draw the shapes of the molecule CO₂ and SO₂ and include both bonding pairs and lone pairs of electrons. (2 marks)

September 2009 Paper 2 Number 1a

a) Global warming through greenhouse gas emissions is the biggest environmental challenge to civilisation. the principal greenhouse gas is CO₂ and recently there has been research on the removal of atmospheric CO₂ by its reaction with minerals similar to CaO.

i) Calculate the enthalpy change of the reaction between CaO and CO₂ given the following enthalpy changes of formation ( $\Delta H_f$ ) in kJ mol-1: CaO_(s)(s) -635, CO_2(g) -390, CaCO_3(s) -1207

ii) Explain why the entropy change for the reaction may not allow the reaction to occur.