Chemistry - Rates of Reaction

Collection under water

Errors:

1. Some gas escapes, especially before the bung is inserted

2. Inserting the bund displaces air

3. Some gases dissolve in water (CO2 and O2 particularly)

Using a gas syringe

Errors:

1. Some gas escapes, especially before the bung is inserted

2. Inserting the bund displaces air

3. Temperature is not constant (of gas) [tends to get hotter → expansion]

Measuring change in mass

BEST METHOD

Errors:

1. Some gas escapes, especially before the cotton wool goes in

2. Some gas may dissolve in the liquid

Measuring the time taken for cross to be invisible

Errors:

1. Relies on judgement / eyesight / size of cross

Surface area

More particles of solid are exposed so more frequent collisions

Concentration

More particles in the same volume of liquid = more frequent collisions

Pressue

More particles in the same volume of gas so more frequent collisions

Temperature

Particles gain more kinetic energy so move faster so collide more frequently. This also means that a higher percentage of particles have higher energies than the activation energy so a higher percentage of collisions are successful

Adding a catalyst

Provides an alternative reaction route with a lower activation energy so a higher percentage of particles have higher energies than the activation energy so a higher percentage of collisions are successful

Catalyst

A substance that increase the rate of reaction but is chemically unchanged at the end of the reaction (not used up)