Reaction Rates
- Created by: Emily Cartwright
- Created on: 26-05-14 17:42
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- Reaction Rates
- The rate of reaction is the rate of change of the concentration of a reactant or product with time
- Effect of Concentration
- The rate of reaction increases as the concentration increases
- The reason is that for chemical reactions to occur, an effective collision has to take place between the particles of the reactants
- If the concentration of one or more reactants increases, then the particles are closer together and so they collide more often
- The reason is that for chemical reactions to occur, an effective collision has to take place between the particles of the reactants
- For gases, increasing the pressure increases the concentration and therefore increases the rate of reaction for the same reason
- The rate of reaction increases as the concentration increases
- The Boltzmann distribution and activation energy
- Even at the same temperature, the energy of particles varies considerably. Some are moving slowly with low kinetic energy, but some are moving faster with more kinetic energy
- The Boltzmann distribution is a way of showing the number of particles that have particular energies
- Even at the same temperature, the energy of particles varies considerably. Some are moving slowly with low kinetic energy, but some are moving faster with more kinetic energy
- The effect of temperature changes on rates of reaction
- Raising the temperature increases the rate of reaction. This is because;
- As the temperature increases, so does the proportion of molecules that have an energy greater than the activation evergy
- Consequently, when molecules collide, it is more likely that this will successfully lead to a reaction. This is the main reason for the rate increasing with temperature
- As the temperature increases, the molecules are, on average, moving faster and therefore collide more often. This is generally a much smaller effect
- As the temperature increases, so does the proportion of molecules that have an energy greater than the activation evergy
- We can therefore conclude that as the temperature increases, there is an increased frequency of successful collisions
- Raising the temperature increases the rate of reaction. This is because;
- Catalysts
- A catalyst increases the rate of reaction, but is not used up in the process. It does this by providing an alternative pathway of lower activation energy
- The effect is that a higher proportion of molecules have an energy greater than the activation energy, and hence, successful sollisions are more successful
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