Chapter 18

Changing the conc of a reactant often changes rate. The ROR is proportional the conc of a reactant raised to a power ‘the order of reaction’

Changing the conc of A does not affect ROR so graph is a straight line

-Whatever factor you change the change conc by the rate changes by the same factor -Graph is a straight line through the origin with a posotive gradient

-rate changes by the square of whatever factor you change the conc by. -resulting graph is a curved line of exponential growth from the origin ( graph of rate/ conc squared is a straight line through the origin)

Gives the effect of the conc of all reactants on the ROR calculated as the sum of orders with respect to each reactant

-By gas collection using a conical flask, a gas syringe and a stopwatch. Measure gas volume at regular intervals • By mass loss- use cotton wool to stop spray escaping • By colourimeter if one of the reactants has a colour the intensity will cahnge during the reaction

-Prepare standard solutions of a known concentration of the coloured chemical -Select a suitable filter with the complementary colour to that of the coloured chemical -Zero the colourimeter with distilled water -Measure the absorbance readings of the standard solutions. - plot a calibration curve of absorption against concentration

Gradient/ROR decreases as the reaction progresses. (curved line downward)

Straight line gradient downwards constantv gradient so no change in rate value of gradient= k (rate constant)

The time taken for the concentration of a reactant to decrease to half its original value. Can be measured from any starting point on the graph

1) Calculate k from rate. -Draw a tangent anywhere on the graph and work out gradient (rate) Sub into the equation rate= kx[A] for [A] sub in the conc at the point the tangent was drawn 2) Calculate k from half life use equation k= In2 / t0.5