Reaction Kinetics

draw a new distribution curve, clearly labelled T', for the same mixture of gases at a higher temperature, T';

mark clearly, as H, the position of the activation energy of the reaction at the higher temperature, T'.

Explain the meaning of the term activation energy.

On the energy axis of the graph opposite, mark the position, clearly labelled C, of the activation energy of the reaction when a catalyst is used.

Use your answer to (ii) to explain how the use of a catalyst results in reactions occurring at a faster rate.

Two reactions involving aqueous $\text{NaOH}$ are given below.

In order for reaction 1 to occur, the reagents must be heated together for some time. On the other hand, reaction 2 is almost instantaneous at room temperature.

Suggest brief explanations why the rates of these two reactions are very different.

reaction 1 ........................................................................................................................

reaction 2 ........................................................................................................................

Sketch on Fig. 3.1 the shape of the curve for the same sample of $\text{H}_2(\text{g})$ molecules when the temperature is increased.

Explain why increasing the temperature increases the rate of reaction 1.

State the role of nickel when it is added to reaction 1.

Annotate Fig. 3.2 to show the effect of adding nickel to reaction 1 at temperature $T$.

Use the graph to calculate the average rate of reaction at 20°C during the first 600s. State the units of this rate of reaction.

The experiment is repeated at a temperature of 40°C. This relatively small increase in temperature produces a large increase in reaction rate.

Sketch a graph, on the same axes, to show the expected results when repeating the experiment at 40°C.

The rate of reaction increases when the frequency of successful collisions between reactant particles increases.

Explain why an increase in temperature produces this effect.

Draw a curve on the axes to show the Boltzmann distribution of energy of particles in a sample of gaseous krypton atoms at a given temperature.

Label the curve T1 and label the axes.

On the diagram in (a)(i), draw a second curve to show the distribution of energies of the krypton atoms at a higher temperature.

Label the second curve T2.

Use this information to complete the reaction profile diagram for the formation of $\text{KrF}_2$.
Label $E_a$ and $\Delta H_f$ on the diagram.

Assume the reaction proceeds in one step.

Explain, in terms of activation energy, $E_a$, and the collision of particles, how an increase in temperature affects the rate of a chemical reaction.

Explain what is meant by the term rate of reaction.

Label the graph to show the proportion of 2-bromo-2-methylpropane molecules which have sufficient energy to react.

Use the same axes to sketch the distribution of energies of molecules in a sample of 2-bromo-2-methylpropane at $50\,^\circ\text{C}$.

State the effect of an increase in temperature on $E_{\text{a}}$ for this reaction.

Use the Boltzmann distribution shown to explain why a catalyst increases the rate of this reaction.

With reference to Le Chatelier’s Principle and reaction kinetics, state and explain one advantage and one disadvantage of using a higher temperature.

Define activation energy, $E_A$.

The Boltzmann distribution for the reaction mixture in reaction 1 is shown in Fig. 3.1.
Use the Boltzmann distribution to explain the effect of adding a catalyst on the rate of reaction.

Add a labelled mark, $E_{a_{\text{uncat}}}$, to the diagram to indicate the activation energy in the absence of the catalyst.

State the benefit of using a catalyst in this reaction. Explain how it achieves this effect.

State and explain how an increase in pressure would affect both the rate of reaction and the yield of $\text{SO}_3$ in the Contact process.

rate

yield