=Factors That Affect Reaction Rate= The following factors can affect the rate of a reaction. Collision theory can be used to explain their affect. *Temperature *Concentration *Surface Area (Particle Size) *Catalyst ==Temperature== [image:http://i.imgur.com/lh3katw.png?1] Increasing the temperature increases the kinetic energy of the reactant particles. The particles move more quickly increasing the frequency of collisions. The particles also collide with more energy which increases the likelihood of each collision being successful. Increasing the temperature does not alter the total amount of product that is formed. This is because the amount of reactant particles doesn't change. If the temperature is low it simply takes longer for the same amount of product to be formed. This is why the line representing the reaction at a lower temperature is flatter but still eventually reaches the same height. ==Concentration== [image:http://i.imgur.com/yjJeT16.png?2] Increasing the concentration means there are more reactant particle in a given space (volume). This increases the chance that reactant particles will collide. The increased frequency of collisions results in a faster rate of reaction. ==Surface Area / Particle Size== [image:http://i.imgur.com/Zz6gRa9.png?1] If one of the reactants is a solid, only the particles at the surface can partake in the reaction. Breaking the reactant into smaller pieces increases the surface and more particles are exposed to the reaction mixture. This results in an increased frequency of collisions and therefore a faster rate of reaction. This is why powdered magnesium reacts more quickly that a lump of solid magnesium. Increasing surface area increases the rate of reaction, but does't alter the total amount of product formed. ==Catalyst== [image:http://i.imgur.com/dgZCv4A.png?1] A catalyst is a substance that speeds up a reaction, but is not used up in the process (is not a reactant). Catalysts reduce the activation energy of a reaction. Activation energy is the energy needed to initiate a chemical reaction. A certain level of energy is often needed in order to break existing bond, before new bonds can be formed an energy is released. This can be seen on the graph as a 'hump' -energy must first be put into the reaction (the graph rises), before energy is released from the reaction (the graph fall). A catalyst means that less energy is needed to get the reaction started. ===[image:http://i.imgur.com/OCelOZm.gif?1]=== Some catalysts (such as enzymes) increase the rate of reaction by temporarily binding with the reactants and providing them with the correct orientation for a successful collision to occur. A catalyst does not increase the frequency of collisions but increases the likelihood that each collision will be successful.