Topic 9 Kinetics I 2️⃣

Change in concentration ————————————- Time for change to happen

Draw a tangent to the curve at the point rate of reaction is to be measured Find the gradient (change in y/change in x)

How fast one of the products/reactants is being used up/formed

The two molecules must collide with sufficient energy to cause a reaction (activation energy) The two molecules must collide in the correct orientation

When the shapes of the molecules influence the reaction we say there is a ‘steric factor’ involved. In some cases the atoms/groups of atoms in a molecule can hinder the course of a reaction (ie. If particularly large it can get in the way of the attacking species) If this happens we say the reaction suffered from ‘steric hinderance’

For many reactions if the conc of a solution is increased then the frequency of collision between reacting solute particules also increases. This is because they are closer together as there are more of them in a given volume of solution so the frequency of successful collisions increases

For a reaction in which molecules collide and react in gas phase an increase in pressure will cause an increase in rate of reaction This is because there will be more reactant molecules in a given volume of mixture so the frequency of successful collisions will increase

For heterogeneous reactions involving a solid, a larger sa will result in an increased rate of reaction

Molecules in a sample have a wide range of energies In order to estimate what fraction of collisions will have the required Ea, we need to know the energy distribution of the molecules

Peak moves to right (higher energy) with a lower height Area under curve is the same

The Ea line would shift to the left Curve would remain the same exactly

Peak remains at the same energy Peak has a stretched shape |

At a higher temp particles have more KE Greater proportion can exceed the Ea & therefore collide with sufficient energy for a reaction to take place More successful collisions = faster rate of reaction

Lowers Ea by providing an alternative pathway (may be an intermediate or a sa for reaction to occur on) Rate of reaction is increased They are regenerated at the end

Enthalpy level of products is above that of the reactants

• They increase the rate of a chemical reaction meaning that more of the desired product can be made in a given time period • Reactions can take place at lower temperatures resulting in a decrease in the energy costs to the manufacturer

A catalyst that is in the same state as reactants They work by reacting with the reactants to form an intermediate which breaks down to give products and regenerated catalyst

Cl radical in ozone depletion Sulphuric acid when making esters

Catalyst is in different state to reactants (usually solids) Works by providing a surface on which the reaction can take place

Use of iron in the Haber process Use of Vanadium (V) oxide in the contact process

One of the reactants approches the catalysts surface and settles onto an active site - ADSORPTION Another reactant approches the catalyst Re-arrangement of electrons takes place- REACTION The products are released from the surface- DESORPTION