6.2.4

6.2.4 Predict and explain, using the collision theory, the qualitative effects of particle size, temperature, concentration and pressure on the rate of a reaction

Independent Variable	Time and surface area of Marble chips
Dependent variable	Volume of gas produced from the reaction
Controlled variables	Concentration and volume of hydrochloric acid, volume of water kept at without air bubbles in the turned measuring cylinder and the mass of marble chips. Also keep in mind the room temperature
Explanations	It is expected that with larger surface areas like powder and smaller marble chips that the reaction will be significantly faster because the particles in the hydrochloric acid has a higher chance of coming in contact and colliding with the calcium carbonate. Therefore the prediction is that the higher the surface area the faster the rate of reaction.
Gradient	The gradient in this case indicates the rate of reaction or the speed at which the reaction is taking place (see definition of rate of reaction)
Units of gradient	cm3 per second
Differences in results	In many cases the results do not seem to support the expected prediction as powder and the smaller marble chips were much slower than the medium sized chips. To some extent the beginning of the reaction where the gradient is steepest for all of these reactions seem to fit the general trend.