Factors that Affect the Rate of Reactions Lesson

Factors that Affect the Rate of Reactions Lesson 13

Review of Particle Theory 1. 2. 3. 4. All Matter is made up of extremely tiny particles Each Pure substance has its own kind of particles, different from the particles of other pure substances Particles are always moving. Particles at a higher temperature are generally moving faster, on average than particles at a lower temperature. Particles attract each other

Collision Theory n Everything that happens in a chemical reaction happens between atoms and molecules. Every material is made up of molecules and ultimately atoms. A chemical reaction involves a collision between reactant atoms and molecules, resulting in breaking of some chemical bonds and creation of new ones, ultimately creating new products.

Collision Theory n Collision theory is based on the assumption that for a reaction to occur it is necessary that the reacting species (atoms or molecules) to come together or collide with one another. n The exact energy required for a particular old bond to be broken and a new one to be formed is called the 'Activation Energy'. This is the threshold energy at or beyond which, if the collisions occur, new bonds form.

4 Factors that affect rates of reactions 1. Surface Area n By increasing surface area, the number of molecules exposed for collisions is increased. This allows more collisions between molecules to occur and increases the rate of reaction.

4 Factors that affect rates of reactions 2. Effect of Temperature on Rate of Reaction n One way of increasing the number of molecules that undergo reaction is raising the temperature of the reaction solution. When the reactants are heated, they bounce and contact more vigorously with other reactant molecules. This increases the rate of reaction.

4 Factors that affect rates of reactions 3. Effect of a Concentration on Rate of Reaction n Concentration is defined as the number of molecules of reactants per unit volume. The more the concentration of reactant molecules, the higher the probability of collision due to their sheer number. Excess concentration may have no effect if one of the reactants is used up and the reaction goes into saturation.

4 Factors that affect rates of reactions 4. Effect of a Catalyst on Rate of Reaction n Catalysts, are chemicals or substances that catalyze or promote a chemical reaction to occur and remaining unchanged in the end. They are like parts of an assembling mechanism that help making the final product but then detach themselves from it. They lower the activation energy.

n Rates of Reaction Lab