18.3 rate-concentration graphs and initial rates

zero order rate concentration graphs features

• horizontal straight line graph with zero gradient

• the intercept on the y axis gives the rate constant K

• the reaction rate does not change with increasing concentrations

first order rate concentration graphs features

• straight line graph through the origin

• rate is directly proportional to concentration

• the rate constant can be determined by measuring the gradient of the straight line of this graph

second order rate concentration graphs features

• an upwards curve with increasing gradient

• as this rate concentration graph is a curve, the rate constant cannot be obtained directly from this graph

clock reaction

• way of obtaining the initial rate of reaction by taking a single measurement

• the time t from the start of an experiment is measured for a visual change to be observed

• initial rate is then proportional to 1/t