18 - Rates

• Measuring the decrease in the concentration of a reactant over time • Measuring the increase in the concentration of a product over time

can only be determined experimentally not by mole ratios

o Changing the concentration of the chemical has no effect on the rate of the reaction

No

o Rate = K // y-intercept

o The concentration of the chemical is directly proportional to the rate of reaction, e.g. doubling the concentration of the chemical doubles the rate of reaction

o Rate = gradient

o The rate is directly proportional to the square of the concentration of that chemical, e.g. doubling the concentration of the chemical increases the rate of reaction by a factor of four

o Upward curve = plot rate against conc squared = straight line = k = gradient • gradient of straight line

sum of the powers of the reactants in a rate equation

• From the above table, that is experiments 1 and 2 o The [(CH3)3CBr] has doubled, but the [OH-] has remained the same o The rate of the reaction has also doubled o Therefore, the order with respect to [(CH3)3CBr] is 1 (first order)

• From the above table, that is experiments 1 and 3 o The [OH-] has doubled, but the [(CH3)3CBr] has remained the same o The rate of reaction has increased by a factor of 4 (i.e. increased by 22) o Therefore, the order with respect to [OH-] is 2 (second order)

Rate = k [(CH3)3CBr] [OH-]2

Use one row from table

• In colorimeter – wavelength of light passing through a coloured solution is controlled using a filter • Amount of light absorbed is measures

• In a zero-order reaction, the concentration of the reactant is inversely proportional to time • When the order with respect to a reactant is 0, a change in the concentration of the reactant has no effect on the rate of the reaction

gradient= rate constant k

• In a first-order reaction, the concentration of the reactant decreases with time o The graph is a curve going downwards and eventually plateaus: