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Ahmed Zewail was an Egyptian-American chemist who won the Nobel Prize in Chemistry in 1999 for his work in the field of femtochemistry. Femtochemistry is the study of chemical reactions that occur on timescales of femtoseconds, or one quadrillionth of a second. Zewail's research made it possible to observe and study chemical reactions in real time, which led to a better understanding of the fundamental processes that drive chemical change.