Science, Tech, Math › Science Half-Cell Definition in Chemistry Share Flipboard Email Print Daniell cell electrochemistry may be written as two half-reactions. corbac40 / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated January 13, 2020 A half-cell is half of an electrolytic or voltaic cell, where either oxidation or reduction occurs. The half-cell reaction at the anode is oxidation, while the half-cell reaction at the cathode is reduction. Half-Cell Example The electrochemical reaction of a Daniell cell may be written as two half-cells. The original equation is: 2H+(aq) + 2e- → H2(g) The half-cells or half-reactions are: Zn → Zn2+ + 2e− (for the reaction at the anode or Zn) Cu2+ + 2e− → Cu (for the reaction at the cathode or Cu) Source Andrews, Donald H.; Richard J. Kokes (1962). "Electrochemistry." Fundamental Chemistry. New York: John Wiley & Sons, Inc.