Kinetics Jack Wang Chemistry AP

What factors have an effect on the rate of a reaction? The effects on the rate of a reaction are based on the collision theory, which runs on the idea that molecules have to collide in order for an reaction to occur. Factors that are included in this theory include: Concentration Concentration Temperature Temperature Activation Energy Activation Energy Orientation Orientation Surface area of reactants Surface area of reactants Catalysts Catalysts

Concentration As we already know, the rate-laws depend on the concentrations of the reactants in a reaction. As we already know, the rate-laws depend on the concentrations of the reactants in a reaction. The reason for an increase in reaction rate as the concentration increases is because... The reason for an increase in reaction rate as the concentration increases is because... More molecules = More collisions More molecules = More collisions

Temperature Temperature plays a large role in increasing the rate of reaction. Generally, rates of reactions increase exponentially as temperature increases. Temperature plays a large role in increasing the rate of reaction. Generally, rates of reactions increase exponentially as temperature increases. The first reason that temperature increases rates is that temperature increases the velocity at which molecules move. This yields faster moving molecules that collide into each other more often. The first reason that temperature increases rates is that temperature increases the velocity at which molecules move. This yields faster moving molecules that collide into each other more often.

Activation Energy This is the second factor to which temperature plays a role in reaction rates. This is the second factor to which temperature plays a role in reaction rates. As temperature increases, the kinetic energy of molecules increases as well. As temperature increases, the kinetic energy of molecules increases as well. The collision model postulates that the kinetic energy gained from increase in temperature is the source for the activation energy of the reaction. The collision model postulates that the kinetic energy gained from increase in temperature is the source for the activation energy of the reaction.

Activation Energy cont… As molecules gain kinetic energy from temperature, the kinetic energy simultaneously becomes potential energy which is used when the molecules actually collide. The potential energy is then converted to kinetic energy, which is used to break the bonds of the reactant molecules and to arrange and reform the product molecules.

Orientation Another factor that plays into rate of reactions is based off of the fact that some reactions do not occur even though the necessary amount of activation energy is supplied. Another factor that plays into rate of reactions is based off of the fact that some reactions do not occur even though the necessary amount of activation energy is supplied. This is due to molecular orientation This is due to molecular orientation An example of this is the decomposition of BrNO shown on the following slide. An example of this is the decomposition of BrNO shown on the following slide.

Orientation cont… =Br =N =O    No reaction

Surface area of reactants Another factor that plays into the rates of reactions is surface area. Another factor that plays into the rates of reactions is surface area. Since we know that the rate is increased when there are more collisions available, then we can infer how surface area affects the rate as well. Since we know that the rate is increased when there are more collisions available, then we can infer how surface area affects the rate as well. The more sites available for collision, the faster the reaction will be carried out. An example is show on the next slide The more sites available for collision, the faster the reaction will be carried out. An example is show on the next slide

Surface Area of Reactants The rate of reaction here is slower than it could be because the blue molecules are clumped together and prevents some of the blue molecules from coming into contact with the red molecules.

Surface Area of Reactants The reaction rate here is faster than the example on the previous slide because the surface area is greater allowing more sites of contact for the red molecules to come intact with the 20 blue molecules.

Catalysts The role of catalysts in changing reaction rates is that they reduce the activation energy required to start a reaction. Catalysts are important because some reactions that have reaction rates that are too slow are dramatically increased with the input of a catalyst

Catalysts The way catalysts work is that they provide an alternative pathway (that requires less energy) for a reaction to proceed. The way catalysts work is that they provide an alternative pathway (that requires less energy) for a reaction to proceed. A catalyst is a reactant in one reaction and is produced (regenerated) in another reaction. A catalyst does not appear in the final equation of the overall reaction. A catalyst is a reactant in one reaction and is produced (regenerated) in another reaction. A catalyst does not appear in the final equation of the overall reaction.

The End