Kinetics Flashcards
How can we calculate the rate of reactions from experiments?
Measure the concentration of reactants or products (titration)
Measure the volume of gas produced as a product (using a gas syringe)
Measure the change in masses of substances formed (using a balance to weigh the reactants and products)
How do you calculate the rate of reaction from a graph?
Gradient = change in y / change in x = the rate of reaction
Initial rate when t=0
Draw a tangent——> calculate gradient = rate of reaction
What is the rate of reaction?
The change in the concentration of a reactant or product over time.
Rate = change in concentration / time
What factors affect rate of reactions?
Temperature Pressure Concentration Surface area Presence of a catalyst
How does temperature effect rate of reaction?
Increasing the temperature increases the kinetic energy of the molecules and therefore the number of successful collisions increase
Hence the rate of reaction increases
How does pressure effect the rate of reaction?
Increasing the pressure increases the rate of reaction of gases
Therefore the molecules are closer together and more likely to collide and have a successful collisions with energy in excess of the activation energy.
Therefore collisions are more frequent and the rate of reaction increases
How does concentration effect the rate of reaction?
Increasing the concentration increase the number of molecules of a reactant.
Therefore there are more molecules closer together and can collide with and increased number of collisions so the rate of reaction increases
How does surface area effect the rate of reaction?
Increasing the surface are increases the area where a reaction can occur so the rate of reaction increases
How does he presence of s catalyst effect the rate of reaction?
Catalysts provide an alternative pathway for a reaction to take place. The pathway has a lower activation energy and therefore the reaction happens faster.
What does the maxwell boltzman curve show?
The distribution of molecular energies in a gas at a constant temperature.
The majority of molecules have an average energy.
On a Maxwell Boltzmann curve what does the area under the graph represent and the Ea line?
Area under the graph: the total number of molecules in the sample
Ea: activation energy therefore only molecules greater than the activation energy can react
What happens to the Maxwell Boltzmann curve when temperature is increased?
At higher temperature the kinetic energy of molecules increases
The peak moves to the right and is lower
- Molecules move faster as they have more kinetic energy
- Therefore a higher proportion of molecules have an energy above the activation energy.
- There are more successful collisions
- The rate of reaction increases
What happens to the Maxwell Boltzmann curve when a catalyst is present?
Catalysts lower the activation energy of a reaction
Ea moves to the left
- More molecules have an energy in excess of the new lower activation energy
- More successful collisions in a given time
- Rate of reaction increases
What are the roles of catalysts?
Increase the rate of reaction without being used up in the reactions
How does a catalyst work
By providing an alternative pathway for a reaction to take place with a lower activation energy
They react forming an intermediate but are then regenerated later in the reaction
