Rate & Chemical Energy

What was the reaction time, in seconds, when the concentration of the reactant was 0.50 mol l^-1?

• 0.2

• 0.5

• 2

• 5

In which of the following will both changes result in an increase in the rate of a chemical reaction?

• A decrease in activation energy and an increase in the frequency of collisions

• An increase in activation energy and a decrease in particle size

• An increase in temperature and an increase in the particle size.

• An increase in concentration and a decrease in the surface area of the reactant particles.

In Area X

• molecules always form an activated complex

• no molecules have the energy to form an activated complex

• collisions between molecules are always successful in forming product

• all molecules have the energy to form an activated complex.

For any chemical, its temperature is a measure of

• the average kinetic energy of the particles that react

• the average kinetic energy of all the particles

• the activation energy

• the minimum kinetic energy required before reaction occurs

Which of the following is not a correct statement about the effect of a catalyst? The catalyst:

• provides an alternative route to the products

• lowers the energy that molecules need for successful collisions

• provides energy so that more molecules have successful collisions

• forms bonds with reacting molecules.

The relative rate of a reaction which reached completion in 1 minute 40 seconds is

• 0.01 s^-1

• 0.714 s^-1

• 0.010 min^-1

• 0.714 min^-1

A potential energy diagram can be used to show the activation energy (E_A) and the enthalpy change (ΔH) for a reaction. Which of the following combinations of EA and ΔH could never be obtained for a reaction?

• E_A = 50 kJ mol^–1 and ΔH = –100 kJ mol^–1

• E_A = 50 kJ mol^–1 and ΔH = +100 kJ mol^–1

• E_A = 100 kJ mol^–1 and ΔH = +50 kJ mol^–1

• E_A = 100 kJ mol^–1 and ΔH = –50 kJ mol^–1

What correctly describes the activation energy when you change the temperature from T₁ to T₂ ?

• remains the same

• decreases

• increases slightly

• increases hugely

What correctly describes the number of successful collisions when you change the temperature from T₁ to T₂ ?

• remains the same

• decreases slightly

• decreases greatly

• increases

A reaction was carried out with and without a catalyst as shown in the energy diagram. What is the enthalpy change, in kJ mol^–1 , for the catalysed reaction?

• -100

• -50

• +100

• +50