How are reaction rate and equilibrium related?

1 Answer
Aug 24, 2015

They aren't really related, but the rate of reaction, for both sides of a reversible reaction, is equal at equilibrium.


Rate of reaction is quite simply how fast a reaction occurs I.e the time it takes for a set amount if product to be produced. R.o.R can be measured by
A) weighing the substance to see how much gas escapes (obviously this has its limits)
B) using a gas syringe to measure the volume of gas produced
C) timing how long it takes for a mark to disappear beneath an originally clear substance (this only works when precipitatesvae formed)

Equilibrium, however, is to do with comparing the products and reactants produced in a reversible reaction. Because the reaction goes both ways, the products can react with each other to form the reactants. They will continue to react backwards and forwards until there is an equilibrium. This does NOT mean there are no more reactions, it just means that both the forwards (reactant to product) and the backwards (products to reactants) reactions are occurring at the same rate. So the amount of product/ reactant on either side will remain the same.

However, we can alter when this happens to produce more product ( or reactant). This is known as changing the point of equilibrium, but it is not the same as changing the rate of reaction. It just means that the amount of each side will stay the same at a different point .

You can change the point of equilibrium by adjusting temperature and pressure. A high temperature will benefit the endothermic reaction, as there is more energy available, while a low one will favour the exothermic side. Equally, a high pressure will benefit the side with the least gaseous particles, because it will cause them to collide more, whereas a low pressure will move the equilibrium towards the side with the least gaseous particles.

So the only relationship is that when a reversible reaction has reached equilibrium, the forwards and backwards rate of reaction is the same, so products are being produced at the same rate as they are being broken down into reactants. At what point this occurs affects the ratio of products to reactants.

Hope this helps, sorry its so long - I wasn't sure how much you would already know.