year 11 review of collision theory

review of year 11 content

endothermic reactions

• increase in enthalpy

• ΔH positive

Exothermic reactions

• decrease in enthalpy

• ΔH negative

Breaking bonds absorbs energy, and forming bonds releases energy.

ΔH (enthalpy) = H (Products) – H (Reactants)

what must occur for a reaction to take place

for a reaction to take place a sucessfull collision must take place. Most collisions are not successful.

• molecules must collide with suffcicient energy

• collide with suitable orientation

what are partial pressures?

• The relative concentrations of individual gases in a system.

• Changing partial pressure is like changing concentration.

• Total pressure of a mixture of gases is equal to the sum of the partial pressures of the component gases

apply collision theory

Nature of Reactants – The activation energy is associated with the strength

of the bonds to be broken.

Concentration– Increasing concentration = Increased rate of collisions. Increasing Pressure for gases is equivalent to increasing concentration because

it increases collisions.

Subdivision – increases the available surface area for collisions.

Temperature– Increases the average kinetic energy which means more

molecules have sufficient energy to react. Also increased temperature

increases the speeds of the molecules and therefore the rate of collision.

Catalysts – Provide an alternate pathway for the reaction which has a

lower activation energy. (Ea). Both forwards and reverse reactions are

affected.

—Generally operate by forming intermediate compounds in which bond breaking

and rearrangement can occur with less energy.