CHEM 1.5 - KINETICS

activation energy E_a

activation energy is the minimum amount of energy that particles must have in order to react

collision theory

for a reaction to occur, particles must collide with enough energy (at least the activation energy) and in the correct orientation

why do most collisions not lead to a reaction?

because they do not have enough energy or do not collide in the correct orientation

rate of reaction

rate of reaction is the change in concentration of a reactant or product per unit time

maxwell boltzmann graph

the most probable energy is the energy that the largest number of particles in the sample have

area underneath the curve is the no of particles

maxwell boltzmann graph - higher/lower temp

the new curve should only overlap the old one once

higher temp= curve moves to the right and peak becomes shorter. this is because more particles should have higher energy than the E_a whilst the area underneath curve remains the same

lower temp= curve moves to the left and peak becomes longer. this is because less particles should have more energy than the E_a whilst the area underneath curve remains the same

why a small increase in temp can lead to a large increase in rate

because the curve shifts to the right meaning overall a larger amount of molecules have energy greater than or equal to the E_a

effect of concentration on rate of reaction

increased conc = increased rate

particles are closer together and collide more often. more frequent collisions and higher chance of reaction

effect of pressure on rate of reaction

increased pressure = increased rate

particles are closer together and collide more often. more frequent collisions and higher chance of reaction

effect of catalyst on rate of reaction

activation energy moves to the left on the Maxwell–Boltzmann graph, so more particles have energy equal to or greater than the activation energy

catalyst

a catalyst increases the rate of a reaction by providing an alternative pathway with a lower activation energy. it is chemically unchanged at the end of the reaction

what effects Maxwell Boltzmann distribution graphs

ONLY TEMPERATURE !

pressure, concentration etc do not change curve of the graph

they only affect rate of reaction but energy of molecules stays the same