Which are four factors affecting the rate of a chemical reaction and how do these affect the rate constant of the reaction?
For a chemical reaction to occur the reactant particles must collide with each other with the correct orientation and they must also have a minimum energy necessary for the molecules to successfully react, which is termed the "activation energy" of the reaction, Ea. The rate constant of the reaction is dependent on the Ea of a reaction and it is defined by the Arrhenius equation as k = Ae(-Ea/RT), where A is the frequency factor (a constant) and e(-Ea/RT) expresses the fraction of molecules in the reaction mixture which have energy equal or greater than the Ea (note: R = gas constant, T = temperature in K).An temperature increase will lead to increased kinetic energy of the reactant molecules so that a greater proportion of these will have energy equal or greater than the Ea, allowing for more successful collisions, therefore increasing the rate of reaction. As T is a determinant of k (as defined by the Arrhenius equation), k increases as temperature is increased. The addition of a catalyst to the reaction also increases the rate of reaction by reducing the Ea of the reaction by providing a lower-energy alternative route for the molecules to react. This will also affect k: as the Ea is lowered, k increases. Increasing the concentration of reactants will lead to more molecules and therefore to a greater number of successful collisions, speeding up the reaction; k will be left unchanged, as it doesn't depend on concentration. Lastly, increasing the surface area of the reacting compounds (for example breaking down blocks into pieces/powder) will also result in greater molecular contact and therefore more frequent successful collisions, also speeding up the reaction; again, k will not change.
