Ch.18 rates of reaction

change in conc / change in time

mol dm-3 s-1

straight with - grad

downward curve

time take for conc to half constant value in 1st order exponential decay only on conc time graph

ln2 / half life

horizontal straight line

straight line graph through origin + grad

upwards curve plot rate conc ^2 graph = straight line through origin grad = k

. prepare standard solution of known conc of a coloured chemical . select filter with complementary colour . zero with water . measure absorbance readings of standard solutions to plot calibration curve of absorbance against conc . carry out reaction taking absorbance readings at measured time intervals . use calibration curve to transfer absorbance reading into a conc . plot a conc time graph and determine orders

= to the gradient of conc time graph or the y intercept on a rate conc grah

grad of conc time = ROR grad of rate conc = rate constant

grad at t=0 on conc time graph

initial ROR is change in conc / time for a visual change longer a physical change takes the less accurate it is under 15% reactants used is good over that data is not accurate ROR is proportional to 1/t change in conc is assumed to be constant

slowest step in a multi step reaction reactants are in the rate equation orders in rate equation give stoichiometry

increase

ln k = - Ea/R . 1/t + ln A

proportion of molecules that exceed Ea

pre exponential term / frequency factor takes into account the frequency of collisions with the correct orientation rate if no Ea

increase decrease increase