Topic 16.1: Rate expression and reaction mechanism Flashcards
How can the rate law between two reactants (A / B) be determined?
Experimentally
Not from stoichiometric equations
Mathematical relationship of reaction rate with reactant concentration
Rate = k [A]^x [B]^y
Rate constant (k)
Particular for a reaction at a specific temperature
Overall order (a+b)
Sum of the magnitude orders
Method to determine the rate law
The initial rate is worked out using a fixed amount of B and changing the concentration of A.
Zero order reaction
a) Description
b) Rate expression
c) Units of rate constant
a) The rate does not depend on concentration
b) Rate = k
c) mol dm-3 s-
First order reaction
a) Description
b) Rate expression
c) Units of rate constant
a) The rate is directly proportional to concentration.
b) Rate = k[A]
c) s-1
Second order reaction
a) Description
b) Rate expression
c) Units of rate constant
a) The rate is proportional to the square of the concentration.
b) Rate = k[A]^2
c) mol-1 dm3 s-
Third order reaction
a) Description
b) Rate expression
c) Units of rate constant
a) The rate is proportional to the cube of the concentration.
b) Rate = k[A]^3
c) mol-2 dm6 s-
Graphs (Rate vs Concentration)
a) Zero order
b) First order
c) Second order
a) Constant rate
b) Linear rate
c) Square rate
Graphs (Concentration vs Time)
a) Zero order
b) First order
c) Second order
a) Negative linear
b) Negative curve with constant half-life
c) Negative curve with no constant half-life
Half-life definition
Time required for the concentration of a reactant to reach half its initial value.
Half life for a first order rate law
It does not depend on the initial concentration of any reactant, so it remains constant throughout the reaction.
Reaction mechanism definition
Sequence of steps by which a chemical reaction occurs
Elementary reactions definition
Reactions that occur in a single step
