3.1.5.4 Effect of concentration and pressure Quiz: AQA Chemistry, Unit 1

The 20 questions

1. How does increasing the concentration of a reactant affect collision frequency?

   • It increases the collision frequency
   • It has no effect on collisions
   • It changes the activation energy
   • It decreases the collision frequency

2. How does increasing the pressure of a gas affect collision frequency?

   • It decreases the collision frequency
   • It lowers the activation energy
   • It has no effect on collisions
   • It increases the collision frequency

3. Why does increasing concentration increase the rate?

   • Particles move faster at higher concentration, so each collision carries more energy
   • More particles per unit volume means more frequent collisions
   • The activation energy falls at higher concentration, so more collisions succeed
   • The reaction becomes endothermic at higher concentration, so it absorbs energy from the flask

4. Does changing concentration alter the proportion of collisions with energy at or above the activation energy?

   • Yes, it changes the proportion of collisions above the activation energy in every case
   • Yes, it halves the activation energy when the concentration is doubled in the solution
   • Only at high temperature does concentration change the proportion of energetic collisions
   • No, it changes collision frequency, not the proportion with enough energy

5. What happens to a fixed mass of gas when it is compressed at constant temperature?

   • Its pressure and concentration increase
   • Its molar mass changes with the compression process
   • Its particles have no change in energy or spacing
   • Its pressure decreases as the particles spread out more

6. In the investigation of calcium carbonate and hydrochloric acid, what is a common way to follow the rate continuously?

   • Measuring temperature only, at fixed time points
   • Titrating the acid at regular intervals with a burette
   • Measuring the mass loss as carbon dioxide escapes
   • Measuring the pH of the solution only at the end

7. Which measurement is used to follow the rate of the calcium carbonate and hydrochloric acid reaction?

   • Temperature rise only
   • Loss of mass as carbon dioxide escapes
   • Change in colour of the solution
   • Titre volume

8. Doubling the concentration of a reactant doubles the rate. What does this suggest?

   • The rate is proportional to the concentration
   • The rate falls by half
   • The rate is independent of concentration
   • The rate is proportional to 1/concentration

9. At constant temperature, the volume of a gas is halved. What happens to the rate of a gas reaction?

   • It increases, because collision frequency roughly doubles
   • It becomes zero, because the gas stops reacting once it is compressed
   • It halves, because the particles have less room to move in the container
   • It stays the same, because the temperature has not changed in the container

10. Why does a higher acid concentration make calcium carbonate react faster?

    • Calcium carbonate becomes ionised more readily in concentrated acid, which speeds reaction
    • The reaction becomes endothermic in concentrated acid, so it absorbs more energy
    • Acid concentration changes the activation energy of the reaction at the solid surface
    • More acid particles per unit volume means more frequent collisions with the calcium carbonate surface

11. Which is a valid control variable in an experiment on the effect of acid concentration on calcium carbonate?

    • The volume of gas collected in the gas syringe
    • The mass and surface area of calcium carbonate
    • The concentration of acid, which is the independent variable
    • The time of reaction, measured from the first addition of acid

12. Two sealed gas samples are at 2 atm and 1 atm at the same temperature. How does collision frequency compare?

    • Half as frequent at 2 atm
    • Four times as frequent at 2 atm
    • Twice as frequent at 2 atm
    • The same at both pressures

13. A solution of reactant at 2.00 mol dm-3 is compared with one at 0.50 mol dm-3. Roughly how many times more frequent are collisions at the higher concentration?

    • Four times
    • Eight times
    • Equal
    • Two times

14. Why does increasing pressure at constant temperature not change the energy of colliding gas particles?

    • Pressure changes the frequency of collisions, not the energy distribution, at constant temperature
    • Pressure changes the activation energy, so the energy needed to react is set by the gas
    • Pressure directly raises the energy of each particle, so every collision becomes more energetic
    • Pressure lowers the energy of each particle, so collisions become gentler at higher pressure

15. In an experiment, 40 cm3 of CO2 forms in 40 s with 0.5 mol dm-3 acid, and 60 cm3 forms in 30 s with 1.0 mol dm-3 acid. Which initial rate is greater?

    • Neither produces gas, because the volumes recorded are too small to show any reaction at all
    • The 0.5 mol dm-3 acid, at 1 cm3 per s, because its gas forms more steadily over the time
    • They are equal at 1.5 cm3 per s, because the two gas volumes average out over the reaction
    • The 1.0 mol dm-3 acid, at about 2 cm3 per s compared with 1 cm3 per s

16. Why does increasing concentration not change the activation energy of a reaction?

    • Activation energy is a property of the reaction pathway, unaffected by concentration
    • Increasing concentration lowers the activation energy, because more particles help each other react
    • Concentration sets the temperature of the reaction, which then fixes the activation energy
    • Higher concentration raises the activation energy, because the particles crowd the reaction site

17. Why does compressing a gas have a larger effect on rate than changing the concentration of a liquid by the same proportion?

    • Gas particles are far apart, so compressing a gas greatly increases particles per unit volume
    • Liquid reactions are always slower, so compressing them cannot make any real difference
    • Gas reactions have no activation energy, so compression alone controls the entire rate
    • Liquids have no concentration, so changing their amount has no measurable effect on the rate

18. Why does powdered calcium carbonate react faster than lumps of the same mass?

    • Lumps are more concentrated, so they react more slowly than the finer powder
    • A larger surface area gives more frequent collisions with the acid
    • Powder has a higher activation energy, so the reaction only starts once it is heated
    • Powder acts as a catalyst, lowering the activation energy in the reaction mixture

19. The rate doubles when [A] doubles and does not change when [B] doubles. Which conclusion is correct?

    • The rate is proportional to 1/[A], so doubling [A] halves the observed rate in the flask
    • The rate is proportional to [B] squared, so doubling [B] quadruples the rate in the mixture
    • The rate is directly proportional to [A] and independent of [B]
    • The rate is independent of [A], so doubling [A] has no effect on the observed rate

20. When the concentration of acid is doubled, the reaction time halves. Which conclusion is correct?

    • The rate is inversely proportional to the concentration
    • The rate quadruples
    • Concentration has no effect on the rate
    • The rate is approximately proportional to the concentration

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