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
