Rates Of Reaction Flashcards
Define rate of reaction
Change in concentration of a reactant or a product per unit of time
What is the rate equation?
A + B = C + D
Rate = k(A)^m(B)^n
Units for rate = moldm^-3s^-1
Constants m and n show the order of the reaction with respect to that species.
Total order = m + n
When is the rate constant for a reaction constant?
When the temperature is constant
What is zero order and what does the rate-concentration graph look like?
The concentration of this species has no impact on the rate
Shown on the rate-concentration graph as a horizontal line
Rate = k
What is First-order and what does the rate-concentration graph look like?
The concentration of the species and the rate are directly proportional. Doubling the concentration doubles the rate.
Rate = k(A)
What is second order and what does the rate-concentration graph look like?
The rate is proportional to the concentration of the species squared. Doubling the concentration will increase the rate by 4 times.
Rate = k(A)^2
how can reaction order be worked out?
Using rate-concentration graphs and by the shapes of concentration-time graphs.
What is the concentration-time graph for a zero order reaction?
linear with negative gradient
What is the concentration-time graph for a first order reaction?
curved, check pmt
What would doubling the concentrations of zero, first and second order reactants do to the initial rates?
zero order - o change in initial rate
First order - initial rate doubles
Second order0- initial rate quadruples
Define half life
The time taken for the initial concentration of the reactants to decrease by half. (T1/2)
How can half life be found?
concentration-time graph. The overall order of a reaction affects how the length of the half-life changes over the course of a reaction.
How is the half-life like in a first order reaction?
Constant throughout the reaction. Time taken for concentration to go from 100% to 50% is the same for it to go from 50% to 25%
How could you measure the rate of reaction experimentally? (List some techniques)
Use a colorimeter at suitable intervals if there is a colour change. Colorimeter measures the amount of light absorbed by a solution. Amount of light absorbed is proportional to the concentration of the coloured species.
If gas is involved use a gas syringe to collect volume of gas evolved, or measure the change in mass of the reaction mixture.
What is the equation used to determine rate constant using half life in a first order reaction?
k = ln2 / t1/2
What is the rate determining step?
The slowest step in a reaction with multiple steps
How is the rate determining step linked to the rate equation?
Only species in the rate determining step are in the rate equation.
