21.   The polar regions are particularly at risk because the chemical reaction that destroys ozone is helped by their weather conditions.

22.   The total energy given off is thousands of times more than any conceivable chemical reaction could produce.

23.   Thus chemical reactions occur in the vapor phase.

24.   ...chemical reactions that cause ozone destruction.

25.   The chemical reaction begins as soon as the powder is moistened.

26.   It includes ways to make chemical reactions occur, ways to breed fish, plant forests, light theaters, count votes or teach history.

27.   The Royal Swedish Academy honored Zewail for his groundbreaking work in viewing and studying chemical reactions at the atomic level as they occur.