Reversible Reactions

Reversible reaction = where products of reaction can react to produce original reactants. Presented like this: A + B  ⇌  C + D . Double arrow=reaction can go either way

E.g  Hydrated copper sulfate ⇌ anhydrous copper sulfate (forwards reaction=endothermic + backwards reaction=exothermic)

ammonia + hydrogen chloride ⇌ ammonium chloride

In some reversible reactions forward + backward reaction occur in same conditions & same rate. These reactions said to be in dynamic equilibrium - no overall change in amount of products + reactants, even though reactions ongoing.

Dynamic equilibrium takes place in closed system otherwise products escape (products&reactants don't have to be equal for it to be equal)

The position of equilibrium influenced by 2 main factors: Temp+ conc/pressure

Adding catalyst speeds up time it takes to reach equilibrium but doesn't change position of equilibrium.

Temp->if increased equilibrium shifts to decrease temp=endo direction + if decreased equilibrium shifts to increase temp=exo direction

Conc->increasing=shifts equilibrium in direction that produces less substance

Pressure->increasing pressure shifts equilibrium in direction that produces less gas.

If reversible reaction endothermic in one direction then in other direction will be exothermic (&vice versa)

Le Chataliers' Principle = idea that if you change conditions of reversible reaction, system will try to counteract change=means effect of any changes to system can be predicted

As time goes on rate of reaction decreases in forward reaction as products being formed + reactants being used up.

As time goes on rate of reaction increases in backward reaction as products becoming reactants, therefore rate of reaction increases.