Steady state approximation

Imagine you are playing with a toy car. When you push the car, it moves forward. But at the same time, it starts to slow down because of the friction between the wheels and the floor. This means that the car's speed is changing - it's not staying the same.

In science, we're often interested in how things change over time. We want to know how the concentration of a chemical changes as a reaction happens, for example. But some reactions happen very quickly, and it's hard to keep track of what's happening as everything is changing. That's where the steady state approximation comes in.

The steady state approximation is like a way of taking a snapshot of the reaction at a particular moment in time. We're trying to find a point during the reaction where the concentration of everything has stopped changing. This means that the reaction has reached a 'steady state'.

To do this, we make a guess about what the steady state concentration of each chemical is. We assume that the rate at which each chemical is being produced is equal to the rate at which it's being used up. This is called the principle of microscopic reversibility. We then write down the reaction equations using these guessed concentrations. We can then use these equations to figure out what the actual concentrations of each chemical are.

This approximation isn't always accurate, but it can be a useful way of simplifying a reaction and understanding what's happening at a particular point in time. Just like taking a snapshot of your toy car - you can't see everything that's happening, but you can see a moment in time that can help you understand how it's moving.