CH2 - Rates of reaction

The change in concentration of a reactant or product per unit time

Rate = change in concentration/time

Units = moldm-3s-1

For a reaction to occur between two molecules, an effective collision must take place, resulting in the formation of product molecules

Molecules must colide in the correct oritentiation with enough energy

Increasing concentration/pressure increases rate of reaction as there are more molecules in a given volume, so distance between them is reduced, increasing the chance of a successful collision

Increasing the temperature increases rate of reaction as more kinetic energy so faster movement, and molecules have more energy to react on collision

Reducing the particle size of a solid increases the surface area, so molecules are closer and there's an increase in collisions so an increase in rate of reaction 

Increases the rate of reaction by providing an alternative pathway with a lower activation energy, without being used up or changed

The minmum energy required to start a reaction by breaking bonds

Distribution of molecular energies in a gas, only a minority of molecules have a value that exceeds activation energy 

Curves don't touch axis

At higher temperature, T2 the distribution flattens and peak moves to the right with a lower height. Mean energy of molecules increases, more molecules have sufficient energy to react, rate increases

Only molecules with an energy equal to or greater than Ea can react

Activation energy with a catalyst is lower so a greater proportion of colliding molecules has the minimum energy to react

One in the same phase as the reactants

e.g. concentrated sulfuric acid in the formation of an ester

One in a different phase from the reactants

e.g. Iron in the Haber process

      Ziegler-Natta in the production of high density poly(ethylene)

Biological catalysts

Examples: rennin in dairy industry, yeast and amalyse in brewing industry, lipase and protease in washing powders and detergents 

Benefits: lower temperatures and pressures, operate in mild conditions, biodegradable, form pure products (often)

Change in gas volume

Change in gas pressure

Change in mass

Colorimetry