Kinetics

The collision theory states that for a chemical reaction to take place the particles need to collide with each other in the correct orientation and with enough energy in order to react

they are made or broken

the bonds can be broken and made

An ineffective collision is when particles collide in the wrong orientation or when they don’t have enough energy and bounce off each other without causing a chemical reaction

reactant molecules must collide with “favorable” orientation such that there is direct contact between the molecules to induce the breaking or forming of a bond in space ie the same charge cannot be together as it will repel.

a reaction profile

the minimum energy with which particles need to collide to cause a reaction

Ea

In exothermic reactions the reactants are higher in energy than the products In endothermic reactions the reactants are lower in energy than the products

A catalyst is a substance that increases the rate of reaction without taking part in the chemical reaction by providing the particles an alternative mechanism with a lower activation energy

A Maxwell-Boltzmann distribution curve is a graph that shows the distribution of energies at a certain temperature

The graph shows that only a small proportion of molecules in the sample have enough energy for an effective collision and for a chemical reaction to take place

When the temperature of a reaction mixture is increased, the particles gain more kinetic energy This causes the particles to move around faster resulting in more frequent collisions Furthermore, the proportion of successful collisions increases, meaning a higher proportion of the particles possess the minimum amount of energy (activation energy) to cause a chemical reaction With higher temperatures, the Boltzmann distribution curve flattens and the peak shifts to the right

Therefore, an increase in temperature causes an increased rate of reaction due to: There being more effective collisions as the particles have more kinetic energy, making them move around faster A greater proportion of the molecules having kinetic energy greater than the activation energy

they are faster as less temp is needed so the particles have a lower energy that they need to get to to react these molecules have above threshold energy

-area under curve gives total number of molecules -no molecules can have 0 energy -very few molecules have high energy -the mode is the most probable energy -mean of energy is not the peak of curve it is slightly to the right of it as the curve is not symmetrical -Ea is activation energy

rate of reaction is the change in conc of reactants or products per unit time

moldm-3 s -1

temp pressure for a gas/ conc for a solution surface area of solid presence of catalyst

-graph is lower but further right- as total number of molecules stay the same -higher temp more molecules have an energy greater to or equal to Ea -more frequent collisions -rate is increased -doubling the temp will mean many more molecules have E>/ Ea

10 degrees double

-area under curve increased -more particles present in same volume, so more frequent collisions -more collisions with E>/ Ea -rate is increased the Emp does not change - draw graph higher but peak at same point

-more particles exposed, more frequent collisions -more collisions with E >/ E -rate increased

substance that increases the rate of a chemical reaction without being used up or changed chemically at the end of the reaction