3.1.9 Rate equations Flashcards
What is the rate equation
Rate = k [A]^m [B]^n
What are the m and n in [A]^m and [B]^n
Orders of reaction, restricted to 0,1,2
What is k in the rate equation
The rate constant
What equation shows k varies with temperature
Arrhenius equation
k = Ae^(-Ea/RT)
Name the parts to the Arrhenius equation and the units
k - rate constant - depends on order (m/s)(1/s)(1/ms)
A - Arrhenius constant - ranges
Ea - Activation energy - Jmol-1
R - 8.31
T - Temperature - K
What is the rearranged Arrhenius equation
ln(k) = -(Ea/RT) + ln(A)
OR
ln(k) = -(Ea/R)(1/T) + ln(A)
How is rate of reaction determined
Experimentally
Concentration time graph - zero order
Constant gradient, straight line
Concentration time graph - first order
Curved
Concentration time graph - second order
More curved than first order
How is total order calculated
Add up all the orders of the reactants (m+n)
Concentration-rate graph - zero order
Rate = k
Straight, horizontal line ———
Concentration-rate graph - first order
Rate = k[A]
constant gradient, straight line, directly proportional \
\
\
Concentration-rate graph - second order
Rate = k[A]^2
Curved graph
What does zero order mean
Concentration of this species has no impact on rate
What does first order mean
Concentration of this species is directly proportional top rate
What does second order
Rate is proportional to the square of the concentration of this species
How is overall rate determined
It is determined by the slowest step of the reaction
Therefore the rate equation includes all the species up to and including those in the rate determining step
What is the rate determining step
The slowest step of a chemical reaction
