Rate equations

• Rate determining step is the slowest step in a reaction mechanism which determines the overall rate of reaction
• A reagent will only affect the rate of reaction if it is involved or contributes to the rate determining step
• Pseudo zero order is when reactant is is very large excess, therefore very little is used up causing the concentration to appear constant
• Temperature has an exponential effect on rate of reaction as it effects two factors, speed of particles and activation energy
• Rate is directly proportional to concentration in first order, eg if concentration triples rate also triples
• Rate concentration changes rate remains constant in zero order
• Rate is directly proportional to concentration squared in second order eg. if concentration doubles, rate increases by four
• Method of continuous monitoring: carry out experiments in which the concentration of one reagent is changed, keeping all other factors constant, record dependent variable over a period of time, plot graph, find initial rate for each concentration by determining gradient of tangent at T=0, plot initial rates vs concentrations or log rate v log conc, repeat for all other concs
• Method for measuring to a fixed point: series of experiments in which one concentration is changed while all others are kept constant, keep temp, total volume, stirring rate, apparatus constant, record time taken to a fixed point, plot log rate vs log concentration, repeat for other reagents
• Method for sampling: set up a known volume containing known concentration of ester and OH-, at regular intervals take out a small volume, quickly quench sample by rapid cooling or dilution, use titration to determine moles of OH- in the sample and therefore reaction mixture, plot conc OH-/moles OH- vs time, find initial rate, repeat for other ester, plot log rate vs log ester to find order with respect to ester, repeat for various concs OH-