Chemistry 9701 · AS & A Level · Reaction kinetics

Reaction kinetics — practice question

Nitrosyl bromide, NOBr, may be produced by the reaction shown here: $\text{2NO} + \text{Br}_2 \rightleftharpoons \text{2NOBr}$.
(a)[2]

Explain why this reaction is a redox reaction using oxidation numbers.

(b)[2]

Nitrosyl bromide has a trivalent nitrogen atom. Draw the ‘dot-and-cross’ diagram for NOBr. Show only outer electrons.

(c)

The reaction rate was measured at a range of concentrations of the two reactants, NO and $\text{Br}_2$, and the results below were obtained. The general rate equation for this reaction is written as: rate $= k[\text{NO}]^{a}[\text{Br}_2]^{b}$.

(c(i))[1]

What does the term order of reaction with respect to a particular reagent mean?

(c(ii))[2]

Use the data in the table to deduce the values of $a$ and $b$ in the rate equation. Show your working.

(c(iii))[1]

Use the table data to calculate the initial rate for experiment 4.

(c(iv))[2]

Use the results from experiment 1 to calculate the rate constant, $k$, for this reaction. Include the units for $k$.

(c(v))[1]

Using the rate equation, explain why the rate falls as temperature decreases.

(d)[1]

The reaction between X and Y was investigated: $\text{2X} + \text{Y} \rightarrow \text{Z}$. A possible mechanism is shown below. step 1: $\text{2X} \rightarrow \text{V}$; step 2: $\text{V} + \text{Y} \rightarrow \text{Z}$. The general rate equation for this reaction is written as: rate $= k[\text{X}]^{m}[\text{Y}]^{n}$. Step 1 is the slower step in the mechanism. Deduce the values of $m$ and $n$ in the rate equation.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: N oxidation state changes from $+2$ to $+3$ (so it is oxidised)

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI