2.2 Rates Of Reaction Definitions

Question 1

Activation energy

Answer 1

The minimum energy for particles to collide with for a successful reaction to take place.

Question 2

Catalyst

Answer 2

A substance that increases the rate of a reaction without being changed in chemical composition or amount. They work by providing an alternative reaction pathway with a lower activation energy.

Question 3

Collision theory

Answer 3

Reactions can only occur when collisions take place between particles that have sufficient energy.

Question 4

Colorimetry

Answer 4

This method is used to calculate the concentration of a specific coloured compound in a solution by measuring the extent to which it absorbs certain wavelengths of light. This is measured with a colorimeter.

Question 5

Effects of concentration on reaction rates

Answer 5

As the concentration of reactants increases, the reacting particles get closer together meaning they will collide more often. As a result, there will be a higher rate of successful collisions and a faster rate of reaction.

Question 6

Effects of partial pressure on reaction rate

Answer 6

As the pressure of gaseous reactants increases, the reacting particles get closer together meaning they will collide more often. As a result, there will be a higher rate of successful collisions and a faster rate of reaction.

Question 7

Effects of temperature on the rate of reaction

Answer 7

Increasing the temperature means the particles will have more kinetic energy and so will move faster. If the molecules are moving faster they will collide more often and, since they’ve gained kinetic energy, a larger proportion of the particles will have at least the activation energy. For both these reasons the rate of reaction increases.

Question 8

Energy profile

Answer 8

A graph used to show the relative energy of reaction species (including reactants and products) as a reaction proceeds.

Question 9

Maxwells-Boltzmann distribution

Answer 9

Shows the distribution of the molecular energies in a gas at a constant temperature. The area under the curve indicates the total number of particles present.
Example distribution:
Number of particles

Question 10

Rate of reaction

Answer 10

The measure of the amount of product formed or reactant used over time. The units of rate of reaction may be given as g/s, cm⅜s or mol/s.