Topic 9 and 16 Flashcards
Effect of increasing concentration on rate of reaction
Increase concentration of reaction
Increases number of of reactant specie in a given volume
Increases frequency of collisions between reactant species
Rate of reaction increases
Doesn’t have an effect:
Catalyst is working at max capacity
Certain multistep reactions
Effect of increasing surface area on rate of reaction
Increasing SA:V
Increases the SA for collisions between reactant species to occur on
Increases frequency of collisions
Increases rate of reaction
Effect of increasing temperature on the rate of reaction
Increases energy of reactant species
Faster movement
Increases frequency of collisions
Increases rate of reaction
Increases energy of reactant species
Greater proportion of reactant species exceed the activation energy
Increases frequency of successful collisions
Increases rate of reaction
Catalyst definition and how it works
Substance that speeds up the rate of reaction, but is chemically unchanged at the end of the reaction
Provides an alternative route for the reaction with a lower activation energy.
Heterogenous catalyst
Occupies a different phase to the reactants
Homogeneous catalyst
Occupies the same phase as the reactants
Features of the Maxwell Boltzman distribution curve
X axis: energy
Y axis: number of molecules
Area under the curve = molecules present
Area right of the line = molecules with enough energy to react
Rate equation
rate = k [A]a [B]b
When does the rate constant change
Catalyst or change in temperature
Half life definition
The time taken for the concentration of a reactant to fall to half of its original value.
Independent of initial concentration.
0 order
Rate is independent of the concentration of that reactant
Initial rate against [reactant]: straight horisontal line. y=k
Concentration against time: straight downwards diagonal line
1st order
Change in conc = change in rate
Initial rate against [reactant]: straight upwards diagonal line. Half life constant.
Concentration against time: curved downwards line
2nd order
Change in conc = change in rate to the power of change in conc
Initial rate against [reactant]: curved upwards line
Initial rate against [reactant] squared: straight upwards line
Concentration against time: curved downwards line. Half life not constant.
Why might the rate become higher than expected at the end in an experiment?
The reaction is exothermic, so the temperature increases and a higher proportion of particles have enough energy to react (equal to or greater than the Ea)
Rate determining step definition
The slowest step in the mechanism for a reaction.
