3.1.5.1 Collision theory Quiz: AQA Chemistry, Unit 1

The 20 questions

1. What is the activation energy of a reaction?

   • The energy of the products minus the energy of the reactants in the reaction
   • The minimum energy that colliding particles must have to react
   • The total energy released by a reaction, measured as the enthalpy change per mole
   • The energy contained in one mole of molecules at standard temperature and pressure

2. Why do most collisions between particles not lead to reaction?

   • Products are formed before the collision happens, so the reaction is already complete
   • Collisions are always elastic and produce only heat, so no chemical change takes place
   • Particles never collide in gases, so reactions only happen between solid particles and liquids
   • They do not have the activation energy, so the particles do not react

3. Which statement describes collision theory?

   • Reactions occur when particles have identical masses
   • Reactions occur only in solids
   • Reactions occur when particles are stationary
   • Reactions occur when particles collide with sufficient energy

4. On a reaction energy profile, how is the activation energy shown?

   • As the difference between products and reactants only
   • As the height from the reactants up to the top of the energy hump
   • As a vertical line at the start of the graph
   • As the energy of the catalyst alone

5. What happens to the activation energy when a catalyst is added?

   • It is unchanged
   • It is lowered
   • It is raised
   • It becomes zero

6. Which particles must collide to react?

   • Particles with energy equal to or greater than the activation energy
   • Only ions, because they are the only particles that can gain energy during a collision
   • Only solids, because gases and liquids cannot form the bonds needed in the product
   • Particles with zero energy, which are the slowest and most stable particles in the sample

7. What two factors determine the rate of a reaction in collision theory?

   • The mass of product formed and the volume of the flask in which the reaction takes place
   • The enthalpy change and the entropy change, both measured at constant pressure only
   • The atomic radius of the reactants and their electronegativity on the Pauling scale
   • The frequency of collisions and the fraction of collisions with enough energy

8. Why does raising temperature speed up a reaction in collision theory?

   • Particles become larger when heated, so they collide more often than cold particles do
   • The activation energy increases, so the particles need a greater energy to react together
   • More particles have energy above the activation energy, so more successful collisions occur
   • Collision frequency falls when heated, so fewer particles meet in the same volume

9. Two reactions at the same concentration proceed at different rates. What is the most likely explanation?

   • Temperature is always the same for both reactions, so only concentration can differ
   • They have different activation energies and collision orientations
   • Solutions contain no particles, so the reactions cannot be compared on a rate basis at all
   • Both reactions are reversible only, which means their rates are always identical

10. In an exothermic reaction, how do the energy levels of products and reactants compare?

    • Products and reactants are equal in energy
    • Products are lower in energy than reactants
    • Products are higher in energy than reactants
    • The activation energy is negative

11. A reaction has activation energy 75 kJ mol-1 and an enthalpy change of -40 kJ mol-1. How far is the top of the energy hump above the reactants?

    • 40 kJ mol-1
    • 35 kJ mol-1
    • 115 kJ mol-1
    • 75 kJ mol-1

12. What is the effect of a high activation energy on the rate of reaction at a given temperature?

    • Fewer collisions have enough energy, so the rate is slower
    • The collision frequency becomes larger
    • The enthalpy change becomes larger
    • More collisions have enough energy, so the rate is faster

13. Why must colliding particles have the correct orientation to react?

    • Orientation changes the enthalpy change of the reaction, making it more exothermic overall
    • Orientation determines the mass of the products, so the heaviest product forms first
    • Only collisions with the right orientation break the correct bonds to form products
    • Orientation is irrelevant to reaction, because all collisions break the same bonds equally

14. If the activation energy of a reaction were zero, what would be expected?

    • The rate would be zero, because no collisions could ever occur at a fixed temperature
    • Every collision would be successful, so the reaction would be very fast
    • The reaction would be endothermic, because energy would have to be supplied to start it
    • No reaction would occur, because particles would stick together without forming products

15. Which statement about gas particles at a fixed temperature is correct?

    • Collisions only happen in liquids, because gas particles are too far apart to collide
    • Only a small proportion of collisions have energy at or above the activation energy
    • All collisions have enough energy to react, so every collision in the gas forms products
    • No collisions have enough energy to react, so the gas cannot form any products at all

16. Why is the rate lower at room temperature than at 50 C, even though collisions happen at both?

    • At the higher temperature, a larger fraction of collisions have energy at or above the activation energy
    • At 50 C the activation energy is higher, so fewer collisions are able to react successfully
    • At room temperature particles do not move, so collisions between them almost never happen
    • At 50 C the reaction produces no products, so the rate measured is effectively zero overall

17. A forward reaction has Ea = 80 kJ mol-1 and delta H = -20 kJ mol-1. What is the activation energy of the reverse reaction?

    • 20 kJ mol-1
    • 60 kJ mol-1
    • 80 kJ mol-1
    • 100 kJ mol-1

18. Which factor is NOT part of collision theory?

    • Frequency of collisions between reacting particles
    • Mean bond enthalpy values of the products
    • Orientation of colliding particles relative to each other
    • Energy of the particles involved in each collision

19. Two reactions at the same temperature have the same collision frequency. One has Ea = 50 kJ mol-1 and the other has Ea = 100 kJ mol-1. Which is faster?

    • Neither reacts
    • They are equal
    • The reaction with Ea = 100 kJ mol-1
    • The reaction with Ea = 50 kJ mol-1

20. Which statement about the activation energy of a reaction is correct?

    • It is the same as the enthalpy change
    • It is the total energy released by the reaction
    • It is unchanged by a change in temperature
    • It increases when a catalyst is added

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