Science, Tech, Math › Science Combination Reaction Definition Share Flipboard Email Print Some combustion reactions are combination reactions. Jose A. Bernat Bacete, 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 July 08, 2019 A combination reaction is a reaction where two reactants are combined into one product. A combination reaction is also known as a synthesis reaction. The reaction has the following general form: X + Y → XY Combination Reaction Examples Recognize a combination reaction by examining the number of reactants and products. In this reaction, two reactants become a single product. Combination reaction may occur between two elements, two compounds, or between a compound and an element. The burning of carbon in the presence of oxygen to produce carbon dioxide is a combination reaction: C + O2 → CO2 Magnesium oxide combines with carbon dioxide to form magnesium carbonate in a combination reaction: MgO + CO2 → MgCO3