AS.8 Reaction Rates Flashcards
Rate of reaction
The change in concentration of a substance per unit of time
Rate of reaction units
Moldm-3s-1
Rate of reaction can be increased by:
1)increased temp
2)increased conc of reactants
3)add catalyst
4)increased pressure
5)increased SA of solid reactant
Calculating rate from a graph
Draw a tangent
^Y/^X
Collisions
Unsuccessful - transfers energy but does not result in any new products
Successful - does result in a transfer of reactants into products
Successful collisions can only occur if:
Both particles have energy greater or equal to the activation energy
Activation energy
The minimum amount of energy required for a reaction to occur
Effect of concentration
When conc is increased, we are physically putting more moles of particles into the same amount of space
Increases total collisions
Increases chance of successful collisions
Effect of pressure
Pressure is inversely proportional to volume
As pressure increases, volume decreases
Particles are pushed closer together
Increases frequency of collisions
Increases chance of successful collisions
Effect of temperature
Increase temp, particles have more energy and increase chance of successful collisions
Boltzmann distribution curve - temp
Curve shifts to right and is lower
Greater proportion of molecules have energy greater or equal to activation energy
Catalyst
A substance which increases rate of reaction without being used up in the process
How catalyst works
It provides an alternative route for the reaction which has a lower activation energy
A greater proportion of molecules exceeds new lower activation energy
Homogenous catalyst
Same physical state as the reactants
Form intermediates
Sulfuric acid
Heterogenous catalyst
A different physical state. As the reactants
Fe when making ammonia
Ni when hydrogenating Alkenes
