9.1.1 Collision theory and factors affecting rate Quiz: Pearson Edexcel Chemistry, Unit 9

The 20 questions

1. According to collision theory, what must happen for a reaction to occur?

   • Particles must form ions before colliding so that the electrostatic attraction brings them together
   • Particles must have zero kinetic energy so that they can settle into the correct orientation before reacting
   • Particles must collide with sufficient energy and the correct orientation
   • Particles must remain in the same phase throughout the reaction so that they can collide effectively

2. What is the activation energy of a reaction?

   • The energy released when products form, which is the difference between the reactant and product levels
   • The energy needed to heat the reaction mixture to 100 C before the reaction can start in the flask
   • The minimum energy that colliding particles must have for a reaction to occur
   • The enthalpy change of the reaction, which is the same as the energy barrier that must be crossed

3. Why does increasing the concentration of a reactant in solution increase the rate of reaction?

   • There are more particles per unit volume, so collisions occur more frequently
   • The particles become more energetic, so each collision is more likely to result in a successful reaction
   • The activation energy is lowered by the higher concentration, so fewer collisions need high energy
   • The reaction becomes exothermic at higher concentration, which releases more heat into the solution

4. Why does increasing the temperature increase the rate of a reaction?

   • The number of particles increases during heating because more molecules are formed from the solvent
   • A greater proportion of particles have energy equal to or above the activation energy, and collisions are more frequent
   • The activation energy increases with temperature, so more particles are needed to start the reaction
   • The enthalpy change becomes more negative as the temperature rises, which speeds up the reaction

5. Why does increasing the pressure of a gaseous reaction mixture increase the rate of reaction?

   • The reaction produces more heat when the pressure is raised, which speeds up the reaction in the vessel
   • The gas particles are more concentrated, so collisions are more frequent
   • The activation energy is reduced by pressure, so fewer collisions are needed for the reaction to occur
   • The gas particles gain more energy when the pressure is raised, so each collision has a higher energy

6. Why does increasing the surface area of a solid reactant increase the rate?

   • The solid's activation energy is lowered when it is powdered, so the reaction needs less energy overall
   • The solid becomes a gas when it is finely divided, so the reaction takes place in the gas phase
   • More heat is released by the reaction when the surface area increases, which raises the rate of reaction
   • More particles are exposed to collision at the surface, so collisions become more frequent

7. In an experiment, a reaction takes 40 s. Which quantity is used to compare rates?

   • The temperature of the reaction only
   • The reciprocal of the time, 1/t
   • The mass of product only
   • The time itself, which is directly proportional to rate

8. The gradient of a concentration-time graph is found by drawing a tangent at time t. What does the gradient give?

   • The instantaneous rate of reaction at that time
   • The average rate over the whole reaction
   • The activation energy
   • The equilibrium constant

9. Which description correctly explains the Maxwell-Boltzmann distribution?

   • It shows the enthalpy of each reactant, which is used to predict the enthalpy change of the reaction
   • It shows all particles have exactly the same energy, which is why the rate is constant at each temperature
   • It shows the spread of molecular kinetic energies in a sample, with a few particles having high energy
   • It shows the number of moles of product formed at each time during the reaction in the flask

10. When temperature increases on a Maxwell-Boltzmann curve, what happens to the peak and the area beyond the activation energy?

    • The area beyond the activation energy stays the same
    • The peak height increases but the position stays the same
    • The peak moves to higher energy and the area beyond the activation energy increases
    • The peak moves to lower energy and the area beyond the activation energy decreases

11. Why does a rise of 10 K roughly double the rate of many reactions?

    • The concentration of reactants doubles for every 10 K rise, so there are more particles to collide
    • The activation energy halves for every 10 K rise, so fewer molecules need high energies to react
    • The enthalpy change doubles for every 10 K rise, which speeds up the reaction in a regular way
    • The fraction of molecules with energy above the activation energy increases substantially

12. Which factor does not affect the rate of reaction by changing the number of successful collisions per second in a fixed volume?

    • Concentration of reactants
    • Temperature of the mixture
    • Surface area of a solid reactant
    • The enthalpy change of the reaction

13. What is the effect of increasing concentration on the rate of a reaction between marble chips and hydrochloric acid?

    • The rate decreases because the acid is more dilute, so there are fewer particles to collide with the marble
    • The rate is unchanged because the marble is a solid and its surface is not affected by the acid concentration
    • The rate falls to zero at high concentration because the acid reacts too quickly and stops the reaction
    • The rate increases because more H+ ions are present per unit volume

14. Which graph gives the initial rate of a reaction?

    • A pressure-volume graph at constant temperature
    • A plot of enthalpy against time
    • A plot of pH against volume only
    • A concentration-time graph, by drawing a tangent at t = 0

15. A concentration-time graph shows that the gradient gets less steep as time increases. What does this indicate?

    • The reaction has reached a constant rate
    • The rate is increasing as the reaction proceeds
    • The rate is decreasing as reactant concentration falls
    • The activation energy is increasing

16. What is the effect of a larger surface area of a solid reactant on the rate of a reaction in solution?

    • Rate is unchanged because solids do not react with solutions, so the surface area has no effect at all
    • Rate decreases because the solid is less reactive when its surface is larger and so fewer collisions occur
    • Rate falls because the activation energy rises when the solid is divided into smaller pieces in the flask
    • Rate increases because more particles are exposed for collision

17. What effect does a higher pressure have on a gas-phase reaction in a fixed volume container?

    • It changes the activation energy of the reaction, so the energy needed for each collision is altered
    • It has no effect on the rate because the pressure does not change the number of molecules in the vessel
    • It decreases the rate by spreading the molecules apart, so collisions become less frequent in the container
    • It increases the concentration of gas molecules, increasing collision frequency and rate

18. Which statement describes a successful collision?

    • A collision that forms a catalyst, which then speeds up all subsequent collisions in the mixture
    • A collision that produces a precipitate, which removes particles from the solution and speeds the reaction
    • A collision with energy at least equal to the activation energy and correct orientation
    • Any collision between two particles in solution, whatever the energy and orientation of the particles involved

19. What is the usual description for the activation energy of a reaction?

    • The energy barrier that must be overcome before reactants can form products
    • The energy stored in the products, which is always higher than the energy of the reactants
    • The energy absorbed from the surroundings by the solvent during the course of the reaction
    • The total energy released in the reaction, which is the sum of all the bond energies in the products

20. Which change would NOT increase the rate of reaction of magnesium ribbon with dilute hydrochloric acid?

    • Raising the temperature of the acid
    • Using a more concentrated acid
    • Powdering the magnesium ribbon
    • Diluting the acid with water

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