rate equations Flashcards
A2 kinetics
The rate of a chemical reaction is related to the
concentration of reactants by a rate equation of what form?
A + B –> C + D
Rate = k[A]m [B]n
define the rate of a reaction
change in concentration of reactant or product per unit time
- reminder - do graph work on determining the rate of reaction *
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what are the units of rate?
- mol dm-3 s-1
describe this equation: Rate = k[A]m [B]n
m and n (superscripts) are orders of reaction with respect to reactant A and reactant B
k is the rate constant
define order of reaction
- power to which the concentration of its reactant is raised in the rate equation
what do m and n tell you in: Rate = k[A]m [B]n ?
and what will the overall order of reaction be?
- ## m tells you how conc of reactant A affects rate and n tells you how conc of reactant B affects rate
give examples of how orders of reaction tell you the effect on the rate
- if [A] changes and rate stays the same, order of reaction with respect to A is 0 (e.g. if [A] doubles, rate will stay the same)
- if the rate is proportional to [A], then order of reaction with respect to A is 1 (e.g. if [A] doubles, rate will double)
- if rate is proportional to [A]2 then the order of reaction with respect to A is 2 (e.g. if [A] doubles, the rate will be 2 to the power of 2 which equals 4 so rate quadruples)
in Rate = k[A]m [B]n what is the overall order of reaction?
m + n
describe K’s role in the rate equation?
- k is the rate constant
- a number that links the rate of the reaction to the conc. of the reactants
- bigger the value of k, the faster the reaction
suggest why K (rate constant) increases with temperature
- K always the same for certain reaction at same temp
- but if you increase temp, rate constant rises too
- temp increase = number of collisions between reactant molecules increase and energy of each collision
- but conc and orders of reaction stay the same so k must increase for rate equation to balance
