Rates of Reactions
- Created by: Rebecca Neal
- Created on: 28-04-13 09:33
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- Rates of Reactions
- Things that affects rates of energy
- Temperature
- Pressure of a gas
- Concentration of a solution
- Surface area of a solid
- Catalyst
- Intensity of radiation (photodissociation reactions)
- Collision theory
- At higher concentrations and pressures, the particles are in closer proximity to each other, encouraging more frequent collisions.
- At higher temperatures, a much higher proportion of colliding particles have sufficient energy to react and more particles are able to overcome the activation enthalpy barrier.
- With smaller particles of reactant there is a larger surface area on which the reactions can take place, so the greater chance of successful collisions.
- Heterogeneous catalysts provide a surface where reacting particles may break and make bonds.
- The effect of temperature
- Colliding particles must have a total KE at or above Ea if reaction is to occur
- As the temperature increases, the rate of a chemical reaction also increases. This is because of the distribution of energies among the reacting particles- this distribution is called the Maxwell-Boltzmann distribution.
- Reactions go faster at higher temperatures because a larger proportion of the colliding particles have the minimum activation enthalpy needed to react.
- Activation enthalpy
- Ea is the minimum kinetic energy required by a pair of colliding atoms or molecules before a reaction will occur.
- An enthalpy profile shows how the enthalpy changes as a reaction proceeds.
- Catalysts
- Catalysts work by providing an alternative reaction route with a lower activation enthalpy.
- Successful collisions can take place at a lower energy- this is called lowering the activationenergy barrier.
- Heterogeneous catalysts provide a surface on which a reaction may take place, lowering the energy needed for a successful collision.
- Homogeneous catalysts work by forming an intermediate compound with the reactants.
- Catalysts work by providing an alternative reaction route with a lower activation enthalpy.
- Things that affects rates of energy
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