Rates of Reaction

Rates of reactions can be measured by the:

• Time for a solid to dissolve or form
• Loss in Mass (gas given off) over time
• Volume of Gas collected per time
• Time for a colour to appear or disappear

Collision Theory – in order for a chemical reaction to occur the particles must collide with each other and have sufficient energy to react. The rate of reaction depends on the number of successful collisions there are in a given time. When particles move faster, they have more kinetic energy.

Rates of reaction are affected by:

1. Concentration – adds more particles so they can collide with each other. At the beginning of the reaction, the concentration is at its highest, so the initial rate is the fastest as there are a large number of reactant particles per unit volume and more collisions will occur. As the reactants decrease in concentration, there will be less collisions and the rate slows

2. Particle Size/Surface Area – larger area means there is more room for the particles to roam and will collide easier. The amount of product remains the same but the surface area is different

3. Gas Pressure – an increase in pressure forces the particles to come closer together and increases the chance of successful

4. Temperature – a higher temperature gives particles more energy for collisions and makes the particles move faster so they are more likely to

5. Catalysts – provides particles an alternate way of reacting if the activation energy of the particle is too low, without itself being consumed. g. Iron in Haber process, Enzymes in human body