RATES OF REACTION MHENDS

The Collision Theory 

• For a reaction to occur the reactant, particles must COLLIDE.
• For a collision to result in a reaction it must have enough ENERGY. 
• The amount of energy required for a successful collision is specific to each reaction and is called the ACTIVATION ENERGY. The reason that activation energy is specific to each reaction is that reactant particles may have bonds between them that need to be broken. Every different type of bond requires a specific amount of energy to break it.

Factors Affecting Rate

• Altering TEMPERATURE
• SURFACE AREA of a SOLID
• CONCENTRATION of a SOLUTION
• By using CATALYSTS

Temperature

a. Increasing the temperature of reactant particles increases the rate of a chemical reaction. This is because: a. The reactant particles gain energy and move faster. They therefore collide more often PER UNIT TIME (COLLISION FREQUENCY) so more collisions are successful.

b. More particles are likely to reach the activation energy so that more collisions would be successful.

c. Particles collide with more impact so more collisions are successful.

Surface Area

This applies to reacting solids. Big particles of solid have a low surface area to volume ration. There are few collisions per second on each surface. There are few successful collisions. The rate is slow. Powders have a large surface area to volume ration. There are many collisions per second on each surface. The rate is fast. Increasing surface area does not affect the energy of the reacting particles.

Concentration

This applies to reacting solutions. At high concentration, the particles are close together because there are lots of particles in the volume of solution. The short distance between collisions means many collisions per second. There are more successful collisions. The rate is fast. Increasing concentration does not affect the energy of the particles.

Catalysts

Catalysts speed up a reaction without being used up. They reduce the activation energy by offering an alternative route for the reaction to take place. Catalysts give specific products, can be used in small amounts as they can be reused over and over, used in thin layers as they are often expensive but large surface area to volume ratio increases the effectiveness and reduces cost. They are called enzymes in biology.