Rates and order

Rate of reaction can be found by:

• Measuring decrease in conc. of reactant over time

• Measuring increase in conc. of product over time

Units for rate of reaction

mol dm^-3 s^-1

What is the overall order of reaction?

sum of powers of reactants in rate equations

conc-time graph; 0 order

• reactant conc deacrease while time increases

• straight line

What does grad of line =

rate of reaction / rate constant k

conc-time graph: 1st order

• curve going downwards and eventually plateaus

conc-time graph: 2nd order

concentration of the reactant decreases more steeply with time

For a zero-order reaction the successive half-lives decrease with time

∴ would take less time for the concentration of reactant to halve as the reaction progresses

half-life of a first-order reaction remains constant throughout the reaction

amount of time required for the concentration of reactants to halve will be the same during the entire reaction

second-order reaction, the half-life increases with time

as the reaction is taking place, it takes more time for the concentration of reactants to halve

rate v conc graph: o order

rate v conc graph: 1st order

rate v conc graph: 1st order

• The rate of the reaction increases more as the concentration of the reactant increases

• This means that the rate of the reaction decreases more as the concentration of the reactant decreases when it gets used up during the reaction

• The graph is a curved line

effect of temperature on the rate constant, k:

A + B → C + D

Rate of reaction = k[A][B]

rate of reaction depends on the rate constant, k, and the concentration of the reactants

Increasing the ____ of a reaction increases the rate of a chemical reaction

temp

rate=

K (_)

How find from second order k with graph?

plot rate v conc²

grad=k

equation relating half life to rate constant, for for first order

k=In2/ t_1/2

rate determining step is ___

slow

rate constant and rate of reaction are directly proportional to the _____, then at higher temperatures:

fraction of molecules with energy equal to or greater than the activation energy

• The rate of reaction increases

• The rate constant increases

effect of the higher temperature on the rate constant, k.

increases