Order Of Reactions Flashcards
For a first order reaction
A -> Z
What ways can the rate be expressed as?
Rate= -d[A]/dt = d[Z]/dt= k[A]
How do you derive exponential decay from integrating the rate law
1st order: A -> Z
-d[A]/dt =k[A] 1/[A] x d[A] = -k dt 1) integrate both sides 2) include limits (at t=0, [A]=[A]o) 3) integrate to solve 4) rearrange with log rules 5) exponential to get ride of ln [A]t = [A]oe^-kt - the conc of reactants will follow this
How can you find the rate constant of a first order reaction from the exponential decay? (Integrated logs method)
[A]t = [A]oe^kt 1) take natural logs 2) separate out the logs 3) rearrange the logs ln[A]t = ln[A]o -kt Compare this to a straight line Therefore k is the gradient OR you can simply integrate as normal( you don't have to go from exponential)
What graph will give a straight line for a first order reaction?
ln[A] vs time will give a straight line
The gradient will be -k
How can you find the rate constant if pressure is used rather than concentration?
[A] = -p/RT = p x k
K= 1/RT (A constant at t)
What is a pseudo first order reaction?
This is an elementary reaction where there is more than one reactant
What does a basic second law reaction look like?
A + A -> Z
For a second order reaction, what ways can the rate be expressed as?
A + A -> Z
Rate= 1/2x d[A]/dt= d[Z]/dt =k[A]^2
How can you derive the integrated rates equation for a second order reaction?
Rate= 1/2x d[A]/dt=k[A]^2
1) rearrange to get:
1/[A]^2 x d[A] =-2k dt
1) integrate, consider limits and solve
1/[A]t = 1/[A]o + 2kt
Which graph will give a straight line in a second order reaction?
1/[A] vs time will give a straight line
What is a zero order reaction?
The rate is not affected by concentrated and so concentration of reactants is not included in the rate equation
How can the rate be expressed for a zero order reaction
A -> Z
Rate= -d[A]/dt= d[Z]/dt =k
How can you derive the integrated rates equation from a zero order reaction?
-d[A]/dt =k
Rearrange to d[A]= -k dt
1) integrate, limits and solve
[A]t=[A]o -kt
What is the 1st order integrated equation?
ln[A]t= ln[A]o -kt
Gradient= -k
What is the second order integrated rates equation?
1/[A]t= 1/[A]o + 2kt
Gradient= 2k
What is the zero order rates equation?
[A]t = [A]o - kt
Gradient= -k
What graph will give a straight line for zero order?
[A] vs time will give a straight line
