Rate Equations

the change in conc of a reactant or product per unit time

rate= change in conc / time

• conc change = take samples from a reaction at regular intervals in time and carry out a titration to measure the conc • gas evolving experiments = measure the volume of gas evolved, usually with a syringe, or set the system on a balance and measure the decrease in mass as the gas is released • colour change = measure the colour change during an experiment with a colorimeter • pH change = use a pH meter to follow the pH change during a reaction

the conc of species doubles, the rate is unchanged

the conc of species doubles, the rate also doubles

the conc of species doubles, the rate is 2^2 the conc of species triples, the rate is 3^2

the sum of the orders of all the reactants

• temp is a measure of the amount of energy that molecules have on average -the higher the temperature, the more energy molecules have • only particles with energies equal to or greater than the activation energy will react • increasing the temp increases the number of particles with energy equal to or above the activation energy, leading to more frequent successful collisions • the rate or reaction increases and therefore the rate constant increases

the rate constant roughly doubles for energy 10 degree increase in temperature. Doubling the rate constant will double the rate.

k = Ae^(-Ea/RT) k= rate constant A= Arrhenius constant Ea= activation energy (J mol-1) R= gas constant (8.31 JK-1 mol-1 ) T= temperature (K)

• the temp must increase - particles will move faster with more energy and are therefore more likely to collide with energy equal to or greater than the activation energy. Consequently, the rate of reaction increases. • The activation energy must decrease- a reaction with low activation energy requires less energy for successful collisions, so more collisions will have energy equal or greater than the activation energy. Therefore, the rate of reaction increases. This requires a catalyst

ln k = -Ea/RT + ln A y= mx + c lnk= y m= -Ea/R x= 1/T c= lnA

Ea - -gradient * R R = gas constant

gradient= -Ea / R

the initial rate is drawn at t=0 the initial rate is represented by the steepest gradient. this is the fastest rate at any point in the reaction

the slowest step in the reaction mechanism of a multistep reaction

the order indicates how many molecules of the reactant are involved in the rate- determining step (RDS), either directly or by forming an intermediate