Zero order with respect to reactant
Changing conc. of reactant has no effect on rate
First order with respect to reactant
Rate is directly proportional to conc. of reactant
Second order with respect to reactant
change in rate= change in conc. squared
How is overall order of reaction calculated?
Sum of individual orders
Units of k for a first order reaction
S-1
Units of k for a second order reaction
Mol-1 dm3 s-1
Units of k for a zero order reaction
Mol dm-3 s-1
How could you measure rate of reaction experimentally?
If there is a colour change: Use a colourimeter at suitable intervals If gas is evolved: use a gas syringe to collect volume of gas Measure change in mass of reaction mixture
Half life
The time taken for concentration of a reactant to decrease by half (t1/2)
Relationship between first order reactions and half life
First order reactants have constant half lives (Draw on the graph)
Equation to determine rate constant in a first order reaction (using half life)
k= ln2/ half life
Rate determining step
The slowest step in a reaction with multiple steps
What affects the value of the rate constant?
Temperature only
Arrhenius equation
ln k= -Ea/RT + ln A
k= rate constant for reaction A= pre-exponential factor (number of collisions between reactant molecules) R= gas constant (8.314) T= temperature in Kelvin Ea= activation energy for reaction (in Joules)
The Arrhenius equation to plot a graph
Graph of lnk against 1/T is a straight line Gradient= -Ea/R Y intercept= lnA
Concentration time graph for a zero order reactant
Concentration time graph for a first order reactant
Rate concentration graph for a zero order reactant
Rate concentration graph for a first order reactant
Rate concentration graph for a second order reactant