reaction rates Flashcards
How fast or slow does a reaction occurs?
The rate of reaction is the change in concentration of a reactant or product in a
specified amount of time e.g. 2 moles L–1 minutes–1.
Rate = Δ[A] / Δt
This is similar to measuring speed – distance per unit of time e.g. 60 km h–1.
How do reactions go from reactants to products ?
Transition state or activated complex
At the transition state there is a 50%
chance of forming product and a 50%
chance of returning to reactants.
What is the collision theory? and what assumption are required to be made?
Requirements for two molecules to react
- the molecules must collide -
Assumption 1:
The rate of a reaction will be proportional to the number of collisions per unit time.
Assumption 2:
The number of collisions between two molecules will
depend on the product of their concentrations.
For the elementary reaction: A + B→ C rate = k[A][B]
2nd requirement
they have to collide in specific manner
need to have specific orientation - the orientation permits reacts
3rd requirement - the molecules must have sufficient energy to react - the molecules must collide with sufficient kinetic energy to overcome the activation energy
What are factors that affect the rate of reaction?
- size of energy barrier to reaction a) chemical nature of the reactants b) rate-acceleterating agents: catalysts
- Frequency of collisions:
a) ability of the reactants to come in contact with each other - (state of reactants, surface area, stirring)
b) concentrations of reactants
c) temperature
- Kinetic energy of molecules
a) temperature
What is the formula for measured rate of reaction? Rate Law.
u = k [A]^n
u = velocity
k = rate constant …. 1M how fast the A is going to P - when the concentration of A is 1M.
n= order of reaction
A =
the measured rate of reaction is proportional to the concentrations of the reactants raised to some power.
rate constant is;
Dependent on temperature
Independent of concentrations
Rate of consumption
when the concentration is 1 M
What is the order of reaction?
with respect to a component is the power to which the concentration of that component is raised in the rate law (n or m)
u = k [A]^ n [B]^m
What is the overall order?
is the sum of the orders of all components (n+m)
Zero: u=k
First: u = k [A]
Second u = [A]^2
What is the half-life? t 1/2
indication of rate of chemical reaction - time it takes for its concentration to fall to half of initial value
What is a catalyst?
increases the rate of reaction
is unchanged chemically at the end of the reaction
is present in the same quantity at the end of reaction
only required in small amount
does not affect the position of equilibrium
** they work by providing an alternate path for a reaction, with a lower energy barrier to reaction**
How does catalyst work?
by providing an alternative pathways for the reaction, where activation energy barrier is lower.
can carry the same reaction at lower temperatures - assists.
Lower Activation energy means more molecules will be able to react.
