Part 2 – Reaction Rates
1. A pupil reacted 3g of calcium carbonate lumps with 50cm3 of 1mol/l hydrochloric acid at room temperature. Suggest three changes that could be made to
(a) speed up this reaction
(b) slow this reaction
In a second experiment, the pupil reacted metals with hydrochloric acid.
(c) Identify the 2 experiments which should be compared to show the effect of particle size on the reaction rate.
(d) State which factor is being studied if experiments C and F are compared.
(e) Assuming the order of reactivity of metals is Mg>Fe>Cu, state which experiment would show the fastest reaction.
2. Use the diagrams in the grid below, answer the questions which follow.
(a) Identify the 2 experiments which should be compared to show the effect of temperature on the reaction rate.
(b) Explain why experiments A and F could not be used to study the effect of concentration on reaction rate.
3. Everyday reactions: use your knowledge of the factors that affect reaction rate to explain the following.
(a) Why do powders that neutralize acid indigestion in your stomach work faster than tablets?
(b) Explain why food is kept fresher for longer if stored in a refrigerator.
(c) Explain why car exhausts rust faster than the underside of cars.
4. The graph below shows the volume of carbon dioxide released when an excess of powdered marble chips react with dilute acid.
(a) Explain why the slope of the graph is steepest at the start of the reaction.
(b) Sketch the graph in your jotter and draw and label the curves you would expect if the experiment was repeated using:
(i) a lower temperature
(ii) marble powder instead of lumps
5. Which two boxes in the grid below show changes which happen when a catalyst is added to a reaction?
6. A group of pupils measured the speed of a reaction between marble chips and dilute acid. As the marble chips reacted, the balance recorded a change in mass. At the end of the reaction, all of the calcium carbonate has been used up.
(a) Explain why the mass decreased during the reaction.
(b) Draw a line graph of mass versus time.
(c) Sketch a line on your graph to show the result you would expect if the same experiment was repeated with a catalyst.
7. A pupil observed that the chemical hydrogen peroxide gives off oxygen gas when it is left sitting in a test tube. She also noted that when she added 2g of potassium iodide to the hydrogen peroxide, the rate at which the oxygen was given off increased.
(a) What name is given to chemicals such as potassium iodide which speed up a reaction?
(b) What mass of potassium iodide would be left at the end of the experiment?
8. Zinc reacts with hydrochloric acid to produce hydrogen gas.
(a) State the test for hydrogen gas.
(b) During the experiment, the test tube becomes warm. What term is used to describe a reaction which gives out heat?
(c) Calculate the average rate at which gas is given off between 10 and 40s of the reaction.
(d) Why would increasing the concentration of the acid increase the rate of the reaction?
9. The graph below was obtained for the reaction between excess Mg and 100cm3 of 1moll-1 HCl (aq).
(a) Use the graph to calculate the average rate in the first 20s.
(b) Sketch the graph in your jotter and add a line to show the graph that would be obtained with:
(i) changing the acid to 100cm3 of 2mol/l HCl(aq)
(ii) changing the acid to 200cm3 of 0.5mol/l HCl(aq)
(c) Explain why the reaction rate decreases as the reaction progresses.
10. The collision theory states that for two molecules to react, they must first collide with one another. Name two conditions necessary for a reaction to follow from this collision.
