collision theory

chemical kinetics is

concerned with the dynamics of chemical reactions such as the way reactions take place and the rate of the process

the collision theory is

particles must collide before a reaction can take place, not all collisions lead to a reaction as reactants must possess a minimum amount of energy and particles must approach each other in a certain relative way to react/ particular orientation

the activation energy is

the minimum amount of energy required for two particles to react

the energies of molecules in a substance are distributed in a pattern called

the maxwell-Boltzmann distribution

the maxwell-Boltzmann distribution shows

that no particles have zero velocity, some have very low and very high velocities, most have intermediate velocities

changing the reaction conditions will

alter the shape of the curve so that the number of particles with energy greater than the activation energy is different

the total area under the curve represents the

total number of molecules in a sample, so it must remain constant

the specific rate of a reaction can be calculated from

empirical data that has been plotted on graphs by drawing a tangent to the curve

according to collision theory in order to increase the rate of reaction

either more frequent collisions and more successful collision

more frequent collisions can be cause by

increasing the particle speed or having more particles present

more successful collisions can be caused by

giving particles more energy or lowering the activation energy

ways to increase the ROR are

increased temp, SA, pressure or concentration, adding a catalyst, using a light source

increased temp increases the ROR because

particles have a higher energy so they overcome the energy barrier and particle speed increases so collisions are more frequent and with greater energy

the MB distribution for increased temperature

the curve shifts to the right because a greater proportion of molecules have energy greater to or equal to the Ea , it gets broader and flatter due to the greater spread of values but the area under the curve stays constant

increased concentration increases the rate of reaction because

there are more molecules of a substance in the same volume meaning they are packed closer together, therefore there are more frequent collisions between and the probability of a collision occurring with enough energy increases so there are more successful collisions

an increased concentration and SA changes the MB diagram as

it doesn’t not shift because it doesn’t change the energy of the individual particle

effect of SA on ROR is

it increases the ROR as it increases the number of exposed reactant particles meaning there are more frequent, successful collisions so the ROR increases

the effect of a catalyst on ROR is

it increases the rate of the reaction by providing an alternative pathway that requires a lower activation energy for the reaction to occur therefore more particles collide with sufficient energy and there are more successful collisions

the effect of catalyst on MB

unchanged in shape but the position of Ea is shifted left so that a greater proportion of molecules have sufficient energy to react

catalysts are used in industry because

they lower the energy costs of the reaction process, allowing lower temperatures and pressures to be used whilst still achieving the same ROR, they can also give a higher atom economy