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2 marksThe Mole Concept

CAPE Chemistry Unit 1 · 2005 · Paper 2 · Question 5(c)(ii)

Hydrazine (N2H4) is used as rocket fuel and reacts with chlorine.

Given ΔH = -420 kJ mol^-1 for the reaction in (c)(i), calculate the enthalpy change when 12.7 g of hydrazine reacts completely.

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  1. 5(a)Explain the meaning of the term enthalpy change of a reaction.[2 marks]
  2. 5(b)Distinguish between exothermic and endothermic reactions by referring to energy profile diagrams and bond energies.[6 marks]
  3. 5(c)(i)Write a balanced equation for the reaction of hydrazine with chlorine to produce hydrogen chloride and nitrogen.[2 marks]
  4. 5(c)(iii)Calculate the enthalpy of reaction for N2H4(l) + O2(g) -> N2(g) + 2H2O(g) (ΔH = -534 kJ mol^-1) if liquid water is formed, given the molar enthalpy of…[4 marks]
  5. 5(d)(i)Suggest why the standard enthalpy of formation of carbon monoxide from C(s) and O2(g) cannot be determined directly by experiment.[1 mark]
  6. 5(d)(ii)Construct an energy cycle diagram showing how standard enthalpies of combustion of carbon and carbon monoxide are used to obtain the standard enthalpy of…[3 marks]

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