IB Chemistry SL Reactivity 2: How much, how fast and how far? questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type

Multiple choice Written

Difficulty

Easy Medium Hard

Question 1

Paper 2Hard8 marks

Aspirin (acetylsalicylic acid) can be prepared by either of the reactions shown in Figure 1. Use the atom economy equation in the data booklet and the following relative atomic masses: $A_\mathrm{r}(\mathrm C)=12.01$ $A_\mathrm{r}(\mathrm H)=1.01$ $A_\mathrm{r}(\mathrm O)=16.00$ $A_\mathrm{r}(\mathrm{Cl})=35.45$

(a)

Calculate the atom economy of Route I, to 3 significant figures.

[2]

(b)

Calculate the atom economy of Route II, to 3 significant figures.

[2]

(c)

For each route, determine the mass of reactant material not incorporated into aspirin, per mole of aspirin formed, on the basis of the balanced reaction. Use your answers to (a) and (b) to assess the claim: “Route II must generate less waste in an industrial process because it has a higher atom economy.”

[4]

Question 2

Paper 2Easy6 marks

A chemist compares the initial rate of a gas-phase reaction at two temperatures, with the same initial reactant concentrations. Figure 1 shows Maxwell–Boltzmann energy distributions for the reactant particles. The activation energy for the reaction is $8.0\ \mathrm{kJ\,mol^{-1}}$

(a)

State what is meant by the activation energy, $E_a$ of a reaction.

[1]

(b)

Use Figure 1.

(i)

Identify which curve represents the higher temperature.

[1]

(ii)

Shade the area under this curve that represents particles with enough energy to react.

[1]

(iii)

Explain why the initial rate of reaction is greater at the higher temperature.

[2]

(c)

A catalyst is added to the reaction. On Figure 1, draw and label a vertical line to show the activation energy for the catalysed reaction.

[1]

Question 3

Paper 2Hard12 marks

At 298 K, dinitrogen tetroxide gas dissociates to nitrogen dioxide gas in two sealed, rigid vessels. Each vessel initially contains only dinitrogen tetroxide. Figure 1 shows the structure of dinitrogen tetroxide.

The concentrations were measured over time. The final readings are treated as equilibrium concentrations for calculating $K_\mathrm{c}$

Time / s	Run A [N₂O₄] / mol dm⁻³	Run A [NO₂] / mol dm⁻³	Run B [N₂O₄] / mol dm⁻³	Run B [NO₂] / mol dm⁻³
0	0.0800	0.0000	0.1200	0.0000
20	0.0650	0.0300	0.0960	0.0480
40	0.0560	0.0480	0.0850	0.0700
60	0.0510	0.0580	0.0820	0.0760
80	0.0500	0.0600	0.0817	0.0767
100	0.0500	0.0600	0.0817	0.0767
120	0.0500	0.0600	0.0817	0.0767

(a)

Use Figure 1 to write a balanced equation, including state symbols, for the dissociation of dinitrogen tetroxide gas into nitrogen dioxide gas.

[2]

(b)

For Run A, calculate the ratio of the increase in [NO₂] to the decrease in [N₂O₄] between $t=0$ and $t=80\ \mathrm{s}$

[1]

(c)

Write the equilibrium law expression for $K_\mathrm{c}$ for the reaction in (a).

[2]

(d)

A researcher claims that $K_\mathrm{c}$ is greater in Run B because its equilibrium concentration of NO₂ is greater. Determine whether the data support this claim. Include calculations for both runs and a conclusion.

[5]

(e)

A student argues that Run B cannot be at equilibrium because the concentrations of N₂O₄ and NO₂ are unequal. Evaluate this argument using the definition of dynamic equilibrium and the time data.

[2]

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