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Rate equations (A-level only)

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Question 20

Compounds TTT and UUU react together in the presence of a hydroxide catalyst.

2T(aq)+U(aq)→V(aq)+W(aq) 2T(aq) + U(aq) \rightarrow V(aq) + W(aq) 2T(aq)+U(aq)→V(aq)+W(aq)

The rate equation for this reaction is

rate=k[T]2[OH−] \text{rate} = k[T]^2[OH^-] rate=k[T]2[OH−]

Table 1 shows how the values of the relative initial rate vary with different concentrations of each species at the same temperature.

Table 1

Experiment[T] / mol dm−3[T] \,/\, \text{mol dm}^{-3}[T]/mol dm−3[U] / mol dm−3[U] \,/\, \text{mol dm}^{-3}[U]/mol dm−3[OH−] / mol dm−3[OH^-] \,/\, \text{mol dm}^{-3}[OH−]/mol dm−3Relative initial rate
10.100.250.052.00
20.100.500.05
30.250.050.50
40.150.400.08
a.

Complete Table 1 by calculating the missing values.

[3]
b.

A suggested mechanism for the reaction is shown:

  • Step 1: T+OH−→TOH−T + OH^- \rightarrow TOH^-T+OH−→TOH−
  • Step 2: TOH−+T→T2OH−TOH^- + T \rightarrow T_2OH^-TOH−+T→T2​OH−
  • Step 3: T2OH−+U→V+W+OH−T_2OH^- + U \rightarrow V + W + OH^-T2​OH−+U→V+W+OH−

Deduce the rate-determining step for this reaction and give a reason for your answer.

[2]

Rate equations (A-level only) Questions

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