4.21 Explain that a catalyst speeds up a reaction by providing an alternative pathway with lower activation energy.

Already mentioned in 4.20

It speeds up a reaction by providing an alternate pathway, so lower activation energy is required.

4.20 Explain the effects of changes in surface area of a solid, concentration of solutions, pressure of gases and temperature on the rate of a reaction in terms of particle collision theory

Surface area
There is more surface that is in contact, so it's more likely that there will be successful collisions that lead to a reaction >> faster rate of reaction

Concentration/Pressure
There's more particles so, again, it's more likely that there will be successful collisions that lead to a reaction >> faster rate of reaction

Temperature
Particles are moving faster, so they collide more frequently. Because of this, there is going to be more successful collisions, which increases the rate of reaction

Catalysts
Catalysts make the reaction require less activation energy, providing an alternate "route" for the reaction

4.19 Understand the term activation energy and represent it on a reaction profile

The activation energy is the minimum amount of energy required for a reaction to occur.

This is a reaction profile:

4.18 Describe the effects of changes in surface area of a solid, concentration of solutions, pressure of gases, temperature and the use of a catalyst on the rate of a reaction

• The more concentrated, the faster the rate of reaction
• The larger the surface area, the faster the rate of reaction
• The higher the temperature, the faster the rate of reaction
• The higher the pressure, the faster the rate of reaction
• Use of a catalyst also increases the rate of reaction. The more there is of the catalyst, the faster the reaction.

4.17 Describe experiments to investigate the effects of changes in surface area of a solid, concentration of solutions, temperature and the use of a catalyst on the rate of a reaction

Surface area

• Put a certain mass of a metal, let's say magnesium, into a beaker with x amount of sulphuric acid in it (let's say 100ml). Do this with a block of it.
• Time the reaction, record results
• Repeat step 1 but use another form (i.e. powder)
• Time the reaction again, record results
• Keep repeating with different forms (i.e. strips, etc.), making sure to always use the same mass of the same metal with the same amount of sulphuric acid.
• You should see that the powder will have the quickest reaction because it has the largest surface area.

Concentration

• Put a conical flask on a mini whiteboard on a table. Draw an x in the middle of the whiteboard. Place the conical flask on top
• Presume that 0.2g of sulphur is produced
• Keep changing the ratio of sodium thiosulfate and water, always adding the same amount of hydrochloric acid and measure how long it takes for the cross to be obscured
• Repeat as required
• From this, calculate the concentration (moles ÷ volume = concentration)

Figure 1: My sad looking drawing of the experiment, but I hope you can tell what I mean

Temperature

• Put x amount of magnesium into y amount of sulphuric acid at room temperature
• Time reaction, record results
• Repeat at different temperatures
• You will see that the greater the temp, the faster the rate of reaction

Use of a catalyst

• Put x amount of hydrogen peroxide into a conical flask with y amount of manganese dioxide
• Time how long it takes for the oxygen to displace all the water in the gas jar
• Repeat, increasing the amount of manganese dioxide each time. Yes, you still have to time the reaction. Keep amount x (of hydrogen peroxide) the same
• You will see that the more catalyst you have, the faster the rate of reaction

Figure 2: My second sad looking diagram...I hope you still have some idea of what I mean...