9P-Rates Flashcards
What’s rate of reaction
The change in concentration of a reactant/product per unit time
What’s the rate equation
Rate= k[A]^m [B]^n
[A] and [B] are concentrations of reactants
m and n are the order with respect to A and B
m+n is the overall order
k is the rate constant
How to measure reaction rate at a given time from a conc-time graph
Draw a tangent to the curve at the given time. Use this to calculate gradient which equals the rate
What other than reactants can affect the rate of reaction
Catalyst
What’s k and what factors affect it
Rate constant
Changes even for the same reaction with different temperatures
If the concentrations of all species in equation are 1mol/dm^3, rate equals k (k times 1 = k)
What’s the order of reaction
the power the concentration of a reactant/product is raised to
It tells us how the rate depends on the concentration of that reactant/product
How to calculate units of the rate constant
0 order, mol dm^-3 s^-1
1st/2nd order, rearrange eq to get k on its own eg units for k= units for rate/units for [A][B]
Ensure units are written as mol dm^-3 as it makes this easier
What’s 0 order
Rate is not affected by concentration of a reactant
Species not included in rate eq
What’s 1st order
Rate is directly proportional to concentration of reactant
[A]
What’s second order
At is proportional to the square of the concentration of a reactant
[A]^2
How to find order from rate-conc graphs
0 order, horizontal straight line, rate unaffected by conc of reactant
1st order, sloping straight line through origin
2nd order, not a straight line, to check plot rate against conc of reactant squared, [A]^2
Practise calculating rate equations from questions as this requires given data
Method for calculating order is written in grey kinetics booklet
What’s the Arrhenius equation
k= Ae^-Ea/RT
k, rate constant, units depend on order of reaction
A, Arrhenius constant, same units as k
Ea, activation energy, j/mol
R, gas constant, given
T, temperature, kelvin (+273 if in degrees)
What is ln k= -Ea/RT + ln A used for
Allows for a graph to be plotted from data
1/t against ln k
How to calculate initial rate of reaction
Draw a tangent at t=0 on a concentration time graph and Calc it’s gradient
Or use initial concentration and time data
What’s the rate determining step
The slowest step in a multi step reaction as it implies the rate for the whole process
How to calculate the rate determining step
- 2B—> B2 (RDS)
- B2 + A —> D + E
Combine equations
sub eq 1 into eq 2 2B + A —> D + E
Rate = k [B]^2
Rate eq comes from RDS each combining equations makes overall eq
Relationship between rate constant against time
Exponential relationship
Modelled by Arrhenius equation
What properties do amino acids have
Acidic properties, carboxylic acid group loses H+
Basic properties, amine group accepts H+
