CIE Nov 2016 v2 Paper 4 Q2

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Most car air bags contain a capsule of sodium azide, NaN3. In a crash, the NaN3 decomposes into its elements. PMT (a) Write an equation for the decomposition of NaN3.[1] (b) Complete the dot-and-cross diagram for the azide ion, N3 . Use the following key for the electrons. electrons from central nitrogen atomelectrons from the other two nitrogen atomsadded electron(s) responsible for the overall negative charge [3] (c) Lattice energies are always negative showing that they represent exothermic changes. (i) Explain what is meant by the term lattice energy.[2] (ii) Explain why lattice energy represents an exothermic change.[1]UCLES 2016 9701/42/O/N/16<br /> (iii) Use the following data and any relevant data from the Data Booklet to calculate the standard enthalpy change of formation, Include a sign in your answer. Show all your working. , of NaN3(s). PMT , of NaN3(s) lattice energy, standard enthalpy change of atomisation, standard enthalpy change, H o, for 1 2 , of Na(g) 1 N2(g) + eN3 732 kJ mol1 +107 kJ mol1 +142 kJ mol1 (g) of NaN3(s) =kJ mol1 [3] (iv) The lattice energy, , of RbN3(s) is636 kJ mol1. Suggest why the lattice energy of NaN3(s), 732 kJ mol1, is more exothermic than that of RbN3(s).[1] [Total: 11]UCLES 2016 9701/42/O/N/16 [Turn over<br />

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