Rate is a measure of the speed that a reaction takes place at. In other words it is a measure of the change that happens in a single unit of time. When measuring rate of a reaction we usually measure the amount of reactant used up per unit of time or the amount of product produced per unit of time. When measuring the amount of product produced, a syringe can be used if the product is a gas. Alternatively, if the gas is allowed to escape during the reaction a measure of mass lost could be used to measure the rate. The rate changes throughout the reaction. The rate is greatest at the start, but gets fewer the reaction proceeds. Rate of reaction can be changed by: Change in concentration of reactants Change in temperature Change in surface area of reactants Use of a catalyst. A reaction goes faster when the concentration of a reaction is increased. A reaction proceeds at a quicker rate when the temperature is raised. When the temperature increases by 10oC, the rate approximately doubles. Increasing surface area of solid reactants, increases the rate of a reaction. Catalysts increase the rate of a reaction by lowering the activation energy. This means more successful collisions will take place over a period of time. A catalyst is a substance that changes the rate of a chemical reaction but remains chemically unchanged.