DRAFT GCSE Chemistry- Rates of Reaction

Rate of Reaction

The time taken for products to form, or the time taken for the reactants to be used up

What is the equation for rate of reaction?

rate of reaction = amount of product produced / time taken

Unit for rate of reaction

g/s or cm³/s

Activation Energy

The minimum amount of energy reactants need to have in order to react when they collide with each other

What do catalysts do to the rate of reaction?

Catalysts speed up the rate of reaction without being used up

How do catalysts speed up the rate of reaction?

By lowering activation energy

Four factors affecting rate of reaction

• Temperature

• Concentration

• Pressure (gases)

• Surface area (solids)

How does temperature affect rate of reaction?

• Particles move faster

  • collide more frequently due to increased kinetic energy

  • resulting in more successful collisions

How does concentration affect rate of reaction?

• In a more concentrated solution, there are more particles in the same volume of water

  • Leads to an increase in the frequency of collisions between reactant particles

    • thus increasing the rate of reaction.

How does pressure (gases only) affect the rate of reaction?

• When the pressure of a gas is increased, the same no. of particles occupy a smaller space

  • Leads to an increase in the frequency of collisions between reactant particles

    • thus increasing the rate of reaction.

How does surface area (solids only) affect rate of reaction?

• Breaking up a reactant into smaller pieces increases surface area

  • Means the other reactant’s particles have more area to work on

  • Leads to an increase in the frequency of collisions between reactant particles

    • thus increasing the rate of reaction.

What is the correlation between line steepness on a graph and rate of reaction?

The steeper the line on the graph, the faster the rate of reaction

What does a flat line of a graph indicate?

All of the reactants have been used up

How can more product be obtained in a reaction?

By increasing concentration

What are the three reactions you can do to measure rate of reaction?

• Precipitation

• Change in Mass

• Volume of gas given off

Method for Precipitation Reaction (colour change)

• A reaction is carried out above a paper with a black cross on it

• When the reactants are mixed, a cloudy solid precipitate forms

• This makes the black cross disappear

How to determine rate of reaction in a precipitation reaction?

The quicker the black cross disappears, the faster the rate of reaction.

Method for change in mass reaction

• A reaction that produces a gas can be carried out on a mass balance.

• When the gas is released, the mass reading will go down.

How to determine rate of reaction in a mass change reaction?

If you take measurements at regular intervals, you can plot a graph to find the rate.

Method for volume of gas given off reaction

A gas syringe can be used to measure the volume of gas emitted

Precautions in volume of gas given off reaction

Although this method is accurate to the nearest cm³, vigorous reactions can blow the plunger out of the end of the syringe.

How to determine rate of reaction in the volume of gas given off reaction

The more gas given off, the faster the rate of reaction