It's difficult to decipher this chemical equation.

Understanding chemical equations is difficult.

We are growing vegetables without using chemical fertilizers.

Oxygen, which is one of the chemical elements, is necessary for us to breathe.

Understanding chemical equilibrium is very important in understanding chemical reactions.

This substance undergoes a chemical change when heat is applied.

In this experiment, you can observe a chemical reaction.

Well then, I'm off.

He admitted that it is difficult to execute the plan, saying 'it is easier said than done.'

It is reported that North Korea has conducted another underground nuclear test.