Use both the 'particle theory' and 'collision theory' to describe chemical reactions.
Define the term 'reaction rate'.
Describe how reaction rates can be measured.
Explain how temperature, concentration and surface area affect reaction rates.
Explain the effect of catalysts on reaction rates.
Explain why the rate of a chemical reaction changes over time.
Carry out a number of investigations into the factors that affect reaction rates.
The study of chemical kinetics includes investigations on how different experimental conditions can influence the speed of chemical reactions and produce information about the reaction’s mechanism and transition states. It also includes the construction of mathematical models that can describe the characteristics of a chemical reaction.
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Chemical kinetics deals with the experimental determination of reaction rates from which rate laws and rate constants are derived. In order for a reaction to occur, a collision must take place. This collision has to be of proper orientation and have sufficient energy to break the necessary bonds.
There are several factors that influence the rates of chemical reactions. For instance, the particle size distribution of a material, which can be deduced using a particle size analyser, will affect the reactivity of solids participating in chemical reactions. The following are other factors:
Reaction rate variation is dependant on which substances are reacting. Fast reactions include acid reactions, the formation of salts and ion exchange. Reactions tend to be slow when covalent bond formation takes place between the molecules and when large molecules are formed.
The physical state, i.e. solid, liquid or gas, of a reactant is also an important factor of the rate of change. When reactants are in the same phase, thermal motion brings them into contact. If they are in different phases, the reaction is limited to the interface between reactants and reactions can only occur at their area of contact. Vigorous shaking and stirring may be needed to complete the reaction.
According to the collision theory of chemical reactions, concentration is an important factor because molecules must collide in order to react with each other. When the concentration of the reactants increases, the frequency of the molecules colliding increases, striking each other more frequently. Increasing the amount of one of more reactants causes the collisions to happen more often, increasing the rate of reaction.
Molecules at a higher temperature have more thermal energy and collision frequency is greater at higher temperatures.
Catalysts are substances used to facilitate reactions but remain chemically unchanged afterwards. The rate of reaction is increased when the catalyst provides a different reaction mechanism to occur with lower activation energy.
When the pressure is increased in a gaseous reaction, the number of collisions between reactants will also rise, increasing the rate of reaction.