Revision notes · Chemistry
Collision theory: for a reaction to happen, particles must collide with enough energy. The minimum energy needed is the activation energy.
What increases the rate
Higher temperature — particles move faster, so they collide more often and with more energy.
Higher concentration (or pressure for gases) — more particles in the same volume, so more frequent collisions.
Greater surface area (smaller pieces) — more particles exposed to react.
A catalyst — provides a route with a lower activation energy, so more collisions are successful.
Ways to measure the rate
Mass loss — put the flask on a balance; the mass falls as gas escapes.
Gas volume — collect the gas in a gas syringe or over water.
Colour change or cloudiness — time how long it takes, e.g. the disappearing cross experiment.