Why do reactions speed up with higher concentrations?

Reactions speed up with higher concentrations because more reactant particles are available to collide and react.

In more detail, the rate of a chemical reaction is determined by the frequency of collisions between reactant particles. This is based on the collision theory, which states that for a reaction to occur, particles must collide with sufficient energy and in the correct orientation. When the concentration of reactants is increased, there are more particles present in the same volume of space. This increases the likelihood of collisions between reactant particles, leading to a higher frequency of successful collisions and thus, a faster reaction rate.

Moreover, the increased concentration also means there is a higher chance that these collisions will have the necessary energy to overcome the activation energy barrier, which is the minimum energy required for a reaction to occur. This is because in a higher concentration, more particles will have kinetic energies equal to or greater than the activation energy.

However, it's important to note that not all collisions result in a reaction. The particles must also collide in the correct orientation for the reaction to occur. While increasing the concentration doesn't directly affect the orientation of collisions, the increased frequency of collisions indirectly increases the number of correctly oriented collisions.

In summary, higher concentrations speed up reactions by increasing both the frequency of collisions and the number of collisions with sufficient energy, thereby increasing the rate of successful reactions.