Topic 7

Chemistry Edexcel GCSE Higher Topic 7

What is the core practical for investigating how changing the conditions affects rate of chemical reaction

• You change the conditions by changing the size of marble chips

  • Smaller chips = larger surface area. So therefore faster rate

• You can also change the concentration of hydrochloric acid

  • Greater concentration = greater number of particles in a given volume. So faster rate

• The independent variable is the size of marble chips or the concentration of hydrochloric acid

• The dependent variable is the production of a gas (this is what you're measuring)

Practical methods for determining rate of reaction

• Measure the loss of mass at regular intervals

  • then a plot a graph of mass lost against time

• Measure the volume of gas given off at regular intervals

  • Then plot a graph of volume against time

Explain how reactions occur when particles collide

• Reactions occur when the particles collide with enough energy

• The minimum amount of energy requires is called activation energy

How can you speed up rate of reaction using collision theory

• In order to increase rate of reaction, you must increase the frequency of collisions

  • This can be done by increasing temperature, pressure, or concentration. Or by using a catalyst

How does changing temperature affect rate of reaction

• Higher temperature means particles have more kinetic energy

• They are moving faster

• Means they collide more frequently and with more energy

How does changing concentration affect rate of reaction

• Higher concentration = more particles in a given volume

• Therefore increases number of collisions

how does changing surface area to volume ratio increase rate of reaction

• Increasing SA:V ratio means there is more areas exposed for collisions

• Means more frequent collisions therefore rate of reaction increases

How does changing pressure increase rate of reaction

• Higher pressure = higher number of particles in a given volume (since there is a smaller space but same number of particles)

• This increases the frequency of collisions