Kinetics: the factsor: 1. Plot the reactant concentration against time.2. Is it a straight line? If so then the order is zero.3. If not, plot In [reactant] against time.4.Is it a straight line? If so the order is first andthe gradient = the rate constant k.5. If not, plot the reciprocal of [reactant] against time.6.Is it a straight line? If so the order is second andthe gradient= the rate constant k.6
6 Kinetics: the facts or: 1. Plot the reactant concentration against time. 2. Is it a straight line? If so then the order is zero. 3. If not, plot ln [reactant] against time. 4.Is it a straight line? If so the order is first and the gradient = the rate constant k. 5. If not, plot the reciprocal of [reactant] against time. 6. Is it a straight line? If so the order is second and the gradient = the rate constant k
Kinetics: the factsWordsWordsandExpressionskineticsrate of reactionrateequation;rateconstantreaction order; the order with respect to A; zero order; firstorder;secondorder;overall order;overall reaction; elementary reaction; rate determining step(rds)chain reaction; heterogeneous reaction; homogeneous reaction7
7 Kinetics: the facts Words Words and Expressions kinetics rate of reaction rate equation; rate constant reaction order; the order with respect to A; zero order; first order; second order; overall order; overall reaction; elementary reaction; rate determining step (rds) chain reaction; heterogeneous reaction; homogeneous reaction
Kinetics: the theoryTHE COLLISION THEORYThis states that to react particles must collide.with enough energy to break existing bonds and with the correct orientation to bring reactive sites closetogetherRELATING THE THEORY TO THE FACTORS AFFECTINGRATEChanges in concentration (orSurface area changes inpressure for a gas ) changeheterogeneous reactions changethe number of particles in athe number of collisionsunitvolumeandhencethebetween the fluid phase (liquidnumber of collisions per unitorgas)andthesolidsurface.time in that volume. If theOnce again, if the number ofnumber of collisions changescollisions changes then therate8the rate will change.will also change
8 Kinetics: the theory THE COLLISION THEORY This states that to react ● particles must collide ● with enough energy to break existing bonds ● and with the correct orientation to bring reactive sites close together RELATING THE THEORY TO THE FACTORS AFFECTING RATE Changes in concentration (or pressure for a gas ) change the number of particles in a unit volume and hence the number of collisions per unit time in that volume. If the number of collisions changes the rate will change. Surface area changes in heterogeneous reactions change the number of collisions between the fluid phase (liquid or gas) and the solid surface. Once again, if the number of collisions changes then the rate will also change
Kinetics: the theoryChanges in temperature change the kinetic energy of the particlesand hence the number of successful collisions with enough energyto break existing bonds and make product particles. The minimumenergy needed for a successful collision is called the activationenergy.Increasing the temperature of the system:1. increases the range of kinetic energies;2. increases the average kinetic energy;3. increases the population of particles with more than theactivation energy (shown by the shaded areas under the graph)T.T2>T,EP12EANo.ofEparticlesReactantsProductsenergy
9 Kinetics: the theory Changes in temperature change the kinetic energy of the particles and hence the number of successful collisions with enough energy to break existing bonds and make product particles. The minimum energy needed for a successful collision is called the activation energy. Increasing the temperature of the system: 1. increases the range of kinetic energies; 2. increases the average kinetic energy; 3. increases the population of particles with more than the activation energy (shown by the shaded areas under the graph)
Kinetics: the theoryAddition of a catalyst can decrease the required activationenergy so that a greater population of particles will collidesuccessfully.A catalyst increases the rate without being used up. It does thisby providing a reaction pathway with a lower activation energythrough:10
10 Kinetics: the theory Addition of a catalyst can decrease the required activation energy so that a greater population of particles will collide successfully. A catalyst increases the rate without being used up. It does this by providing a reaction pathway with a lower activation energy through: