He is an expert in semiotics, and his theories are very profound.

Semiotics is the study of signs and symbols used in society and culture.

This reaction occurs through a chemical process.

He is an excellent chemist who made many discoveries.

He is an expert in petrochemistry.

He is an expert in chemical analysis.

It's difficult to decipher this chemical equation.

Understanding chemical equations is difficult.

We are growing vegetables without using chemical fertilizers.

Understanding chemical equilibrium is very important in understanding chemical reactions.