Chemistry · Oct / Nov 2021 · Paper 42 · Question 4
0620
As printed in the paper
The question as text
Chlorine reacts with carbon monoxide to produce phosgene gas, COCl 2(g). A catalyst is used. Cl 2(g) + CO(g) COCl 2(g) The reaction is exothermic.
Read automatically from the paper; the printed page above is exact.
Show the answer and mark scheme
4(a)[3]
M1 E of making bonds > breaking bonds
M2 bond making releases energy
M3 bond breaking requires energy
4(b)(i)[3]
M1 exothermic mark
horizontal line below energy level to R.H.S. of reactants line
and
labelled COCl 2(g) (1)
M2 activation E mark
activation energy ‘hump’ with upward arrow labelled A / activation energy (1)
M3 energy change mark
one downward arrow labelled ΔH
and
energy change starting from E level of reactants and finishing at E level of products (1)
4(b)(ii)[1]
increases rate of reaction
4(c)(i)[2]
equilibrium shifts to right hand side (1)
fewer moles (of gas) on right hand side (1)
4(c)(ii)[2]
equilibrium shifts to left hand side (1)
(forward) reaction is exothermic (1)
4(d)[3]
M1 bond energy in making bonds
= [(2 × 400) + 745] = 1545 (kJ mol–1)
M2 use of total E change
–230 = [240 + E(C≡O)] – 1545
OR
[240 + E(C≡O)] = –230 + 1545 = (+1315)
M3 E(C≡O)
= [–230 + 1545] – 240 = 1075 (kJ mol–1)
4(e)[3]
M1 all single bonding dot and cross pairs correct
M2 double C=O bond dot and cross pairs are correct
M3 complete diagram is correct
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