It's difficult to decipher this chemical equation.

Understanding chemical equations is difficult.

We are growing vegetables without using chemical fertilizers.

This substance undergoes a chemical change when heat is applied.

In this experiment, you can observe a chemical reaction.

Understanding chemical equilibrium is very important in understanding chemical reactions.

He is an excellent chemist who made many discoveries.

He is an expert in petrochemistry.

I found an old box in the storeroom.

Annam is the old name of Vietnam.