any basic substance that is used in or produced by a reaction involving changes to atoms or molecules

The government has pledged to reduce the amount of chemicals used in food production. 政府承诺减少食品生产中化学制品的用量。

Each year, factories release millions of tons of toxic (= poisonous) chemicals into the atmosphere. 每年，工厂将数百万吨的有毒化学物品排放到大气中。

relating to chemicals

The chemical industry produces such things as petrochemicals, drugs, and rubber. 化学工业生产诸如石化产品、药品、橡胶之类的东西。