Orders of reactions Flashcards
What is the order of reaction?
The power to which the concentration is raised to in the rate law expression
What is the overall order of a reaction?
The sum of the individual co-efficients
What would be the rate law equation with A in first order?
v = k[A]
What is a zero order reaction?
The rate is independent of the reactant concentrations
Does not vary with varying concentrations of reactant
What is the rate of reaction equal to when the reactants are zero order?
Rate constant
What are the units for k for v = k[A] ?
v / [A]
M s-1 / M
= s-1
What are the two ways a second order reaction can be written?
v = k [A] v = k [A][B]
What is always the denominator when you work out the units of k for second order reaction?
M²
What are the units for k for a second order reaction?
M-1 S-1
Do chemical reactions always have to have an integer order?
No
eg. it could be 1/2
What are the two methods for working out rate law?
Method of isolation
Method of initial rates
What is the method of isolation to work out the rate law?
Set up the experiment so only one component changes, eg. A and the other 2 remain constant
This allows you to measure the order of reaction with respect to A
What is the method of initial rates to work out the rate law?
Assume the first portion of the concentration vs time plot is linear
To work out the initial rate, use the equation Change in conc / change in time
Then you can use the initial rate to work out the orders of the reactant
How is the order of a reaction determined?
Experimentally
How is the molecularity of a reaction determined?
It is only a theoretical concept
How is the order of a reaction obtained?
From the rate of the overall reaction
How can the molecularity of a reaction be deduced?
it is deduced from the rate determining step in the proposed reaction mechanism
What type of values can the order of reaction have?
May have a whole number, zero or even fractional value
What type of values can molecularity of a reaction have?
Always a whole number and never zero
How can the order of a reaction not be obtained?
Not obtained from a balanced of stochiometric reaction
How can the molecularity of a reaction be obtained?
from the balanced equation of a single reaction step from a known mechanism
What does the order of reaction not tell you?
Doesn’t give you any information about the reaction mechanism, though it gives some suggestions
What does the molecularity of a reaction tell you?
reveals some fundamental facts about the reaction mechanism
is the order of a reaction able to be changed?
Yes
Is magnitude can change when the reaction conditions are altered
Does the molecularity of the reaction change when the reaction conditions are altered?
No
What is the general equation for the method of isolation?
v = k[A]α [B]β [C]ˣ
What is the general equation for the initial rates method?
α = log v1/v2 / log [A]1/[A]2
Units for zero order?
M s⁻¹
Units for first order?
s⁻¹
Units for second order?
M⁻¹ s⁻¹
