Rates of Reaction Practice Questions

Give evidence from the table that the reaction had finished before $180$ seconds.

Calculate the mean rate of reaction during the first $60$ seconds.

mean rate of reaction = .............................................. $\mathrm{cm^3\ s^{-1}}$

Explain why the rate of this reaction decreases as the reaction proceeds.

Which statement about a catalyst is correct?

Put a cross ( ☒ ) in the box next to your answer.

☐ A A catalyst is used up during the reaction.

☐ B A catalyst increases the rate of reaction and is chemically unchanged at the end.

☐ C A catalyst changes the products of the reaction.

☐ D A catalyst increases the mass of product formed.

A student added $0.50\ \mathrm{g}$ of manganese(IV) oxide to $50\ \mathrm{cm^3}$ of hydrogen peroxide solution. When the reaction had finished, the student filtered off the manganese(IV) oxide, dried it and weighed it.

State the mass of manganese(IV) oxide the student should obtain, and give a reason for your answer.

Enzymes are biological catalysts. Name the process, carried out using enzymes in yeast, that is used in the production of alcoholic drinks.

Describe how a student could use a cross drawn on a piece of paper to measure how long this reaction takes.

Explain why the reaction mixture becomes cloudy.

The student repeated the experiment at different temperatures, keeping all other conditions the same.

temperature in $^\circ\mathrm{C}$	time for the cross to be obscured in s
20	96
30	62
40	41
50	28

State, using the information in the table, the effect of increasing the temperature on the rate of this reaction.

Complete the diagram to show how the student could measure the volume of hydrogen gas produced.

In a second experiment the student collected the gas in a $250\ \mathrm{cm^3}$ measuring cylinder. Only $38\ \mathrm{cm^3}$ of gas was produced.

Suggest a different piece of apparatus the student could use to measure this volume of gas, and give a reason for your choice.

The student then repeated the experiment using the same mass of powdered zinc instead of zinc pieces.

Give two variables that must be kept the same for this to be a fair test.

State the time at which the reaction had stopped.

Calculate the mean rate of reaction during the first $60$ seconds.

mean rate of reaction = .............................................. $\mathrm{cm^3\ s^{-1}}$

The student plotted the results as a graph of volume of oxygen against time and drew a tangent to the curve at $20$ seconds. The tangent passes through the points $(0\ \mathrm{s},\ 3\ \mathrm{cm^3})$ and $(60\ \mathrm{s},\ 48\ \mathrm{cm^3})$.

Calculate the rate of reaction at $20$ seconds.

rate of reaction = .............................................. $\mathrm{cm^3\ s^{-1}}$

In a different reaction, magnesium reacts with dilute hydrochloric acid. The rate of reaction is greater with acid of concentration $73\ \mathrm{g\ dm^{-3}}$ than with acid of concentration $36.5\ \mathrm{g\ dm^{-3}}$.

Explain, in terms of particles, why increasing the concentration of the acid increases the rate of reaction.

In the manufacture of ammonia the pressure of the mixture of nitrogen and hydrogen is increased from $100$ atmospheres to $200$ atmospheres.

Explain, in terms of particles, the effect of this change on the rate of reaction.

State the purpose of the iron in this process.

Describe a method the student could use, including the measurements that should be taken.

Explain why the mass of the flask and its contents decreases during the reaction.

The student suggests using the same method to follow the reaction between magnesium and dilute sulfuric acid.

Explain why this method is not suitable for that reaction.

On the graph, draw the curve you would expect if $0.20\ \mathrm{g}$ of powdered calcium carbonate were used instead of small marble chips. All other conditions are kept the same.

Label this curve P.

On the same graph, draw the curve you would expect if $0.10\ \mathrm{g}$ of the same small marble chips were used, with all other conditions kept the same.

Label this curve M.

Explain, in terms of particles, why the original curve becomes less steep as time goes on.

State the independent variable in this investigation.

State the dependent variable in this investigation.

Give two variables that the student must control in this investigation.

A measure of the rate of reaction is given by $1/t$, where $t$ is the time for the cross to be obscured.

Calculate $1/t$ for the $10\ \mathrm{g\ dm^{-3}}$ sodium thiosulfate solution. Give your answer in standard form to two significant figures.

$1/t$ = .............................................. $\mathrm{s^{-1}}$

A student investigated the reaction between zinc and dilute sulfuric acid.

$\mathrm{Zn + H_2SO_4 \rightarrow ZnSO_4 + H_2}$

In each experiment the student used $1.0\ \mathrm{g}$ of zinc and $50\ \mathrm{cm^3}$ of sulfuric acid of the same concentration. The volume of hydrogen collected in $60$ seconds was recorded.

experiment	form of zinc	temperature in $^\circ\mathrm{C}$	volume of hydrogen collected in 60 s in $\mathrm{cm^3}$
1	pieces	20	14
2	pieces	40	33
3	powder	40	58

Explain, in terms of the behaviour of particles, how these results show the effect of changing the temperature and the effect of changing the surface area of the zinc on the rate of this reaction.

Explain how adding a catalyst increases the rate of a reaction.

A student states: "Adding a catalyst means that more product is formed."

Explain whether the student is correct.

Without the catalyst, $50\ \mathrm{cm^3}$ of gas was produced in $200$ seconds. With the catalyst, $50\ \mathrm{cm^3}$ of gas was produced in $40$ seconds.

Calculate the mean rate of reaction in each experiment and use your answers to state how many times faster the catalysed reaction is.

number of times faster = ..............................................

Calculate the mean rate of loss of mass, in $\mathrm{g\ s^{-1}}$, during the first three minutes.

mean rate = .............................................. $\mathrm{g\ s^{-1}}$

Explain, in terms of particles, why the loss in mass in the first minute is greater than the loss in mass in the third minute.

The student repeated the experiment using the same volume and concentration of acid and the same excess of identical marble chips, but with the acid at a higher temperature.

State and explain the total loss in mass the student would obtain.