Chapter 4 Practice Paper: Rate of Reactions — question paper

Section A: Multiple-choice questions[10 marks]

Choose the one correct answer for each question.

1. 1

   Which change increases both the frequency and the energy of collisions between reacting particles?

   1. Aa higher concentration
   2. Ba higher temperature
   3. Csmaller solid pieces
   4. Da higher gas pressure
   ( )
2. 2

   A gas syringe collects 24 cm³ of gas in 40 s. The mean rate of collection is

   1. A0.6 cm³/s
   2. B1.7 cm³/s
   3. C24 cm³/s
   4. D40 cm³/s
   ( )
3. 3

   Pressure is a rate factor that applies to

   1. Aall reactions
   2. Breactions involving gases
   3. Csolid reactions only
   4. Dsolutions only
   ( )
4. 4

   The same mass of marble reacts with 1.0 mol/dm³ and with 2.0 mol/dm³ acid (both in excess). Both volume–time curves flatten at 64 cm³. This shows that

   1. Athe acids were at different temperatures
   2. Bmore gas formed with the higher concentration
   3. Cthe same amount of marble reacted in both runs
   4. Dthe stronger acid made less gas
   ( )
5. 5

   A large lump of solid reactant is cut into four smaller pieces of the same total mass. The reaction speeds up because

   1. Athe particles gain energy
   2. Bthe total mass increases
   3. Cthe concentration of the solution increases
   4. Dthe surface area exposed to collisions is larger
   ( )

Section B: Structured questions[20 marks]

Answer all questions in the spaces provided. Show all necessary working. Give numerical answers to 3 significant figures where appropriate, with units.

1. 1

   Excess dilute hydrochloric acid reacts with calcium carbonate chips. A gas syringe records the volume of carbon dioxide collected.

   Gas volume against time

   Time / s	0	20	40	60	80
   Volume of CO₂ / cm³	0	34	52	58	58

   1. (a)

      Calculate the mean rate of gas production over the first 20 seconds, in cm³/s.

      mean rate =cm³/s[2]
   2. (b)

      State the time at which the reaction finished and explain how the data shows it.

      [1]
   3. (c)

      Explain why the rate of reaction was fastest at the start.

      [2]
   4. (d)

      State what the flat final height of 58 cm³ represents.

      [1]
2. 2

   A student compares 1.0 g of magnesium ribbon with 1.0 g of magnesium powder. Each is added, separately, to 50 cm³ of the same excess dilute hydrochloric acid at 25 °C, and the time to collect 50 cm³ of hydrogen is measured: ribbon 150 s, powder 40 s.

   1. (a)

      State the variable deliberately changed and two variables kept the same.

      [2]
   2. (b)

      Explain, using collision theory, why the powder reacted faster.

      [2]
   3. (c)

      Predict, with a reason, the effect of repeating the ribbon experiment with acid of double the concentration at the same temperature.

      [2]
3. 3

   A flask containing dilute hydrochloric acid stands on a balance. A plug of cotton wool is placed in the flask neck, then 0.24 g of magnesium is added quickly and the flask re-weighed as it reacts. The balance reading falls from 120.00 g to 119.64 g in 2.0 minutes and then stays constant.

   1. (a)

      Calculate the mean rate of mass loss over the 2.0 minutes, in g/min.

      mean rate =g/min[2]
   2. (b)

      State the purpose of the cotton wool plug.

      [1]
   3. (c)

      Name the gas that escaped and write the equation for its formation.

      [2]
   4. (d)

      Describe the shape of the mass–time graph between 0 and 2 minutes, and explain the shape using collision theory.

      [3]