Chemistry · Oct / Nov 2022 · Paper 42 · Question 5
0620
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Ethane is an alkane which undergoes a photochemical reaction with chlorine as shown. C2H6(g) + Cl 2(g) → C2H5Cl (l) + HCl (g)
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5(a)[1]
CnH2n+2
5(b)[1]
needs ultraviolet (light)
5(c)[1]
substitution
5(d)[1]
hydrogen chloride
5(e)(i)[1]
activation energy
5(e)(ii)[1]
energy (change) of reaction
5(e)(iii)[1]
energy of products is lower than energy of reactants
5(f)[3]
M1 energy needed to break bonds
6 × C–H + C–C + Cl–Cl = 6 × 410 + 350 + 240 = 3050 (kJ / mol) (1)
M2 energy released in making bonds
5 × C–H + C–C + C–Cl + H–Cl = 5 × 410 + 350 + 340 + 430 = 3170 (kJ / mol) (1)
M3 energy change M1 – M2 = –120 (kJ / mol) (1)
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