Science, Tech, Math › Science Single Bond Energies Table Thermochemistry Table Share Flipboard Email Print If the bond energies of the products are greater than that of the reactants, the chemical reaction will be exothermic. An example is the thermite reaction. Andy Crawford & Tim Ridley/Dorling Kindersley/Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules 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 November 04, 2019 Knowing the values for bond energy helps us to predict whether a reaction will be exothermic or endothermic. For example, if the bonds in the product molecules are stronger than the bonds of the reactant molecules, then the products are more stable and have a lower energy than the reactants, and the reaction is exothermic. If the reverse is true, then energy (heat) must be absorbed in order for the reaction to occur, making the reaction endothermic. In this case, the products have a higher energy than the reactants. Bond energies may be used to calculate change in enthalpy, ΔH, for a reaction by applying Hess's Law. ΔH can be obtained from the bond energies only when all of the reactants and products are gasses. Single Bond Energies (kJ/mol) at 25°C H C N O S F Cl Br I H 436 414 389 464 339 565 431 368 297 C 347 293 351 259 485 331 276 238 N 159 222 — 272 201 243 — O 138 — 184 205 201 201 S 226 285 255 213 — F 153 255 255 — Cl 243 218 209 Br 193 180 I 151 Use Bond Energies to Find Enthalpy Change of a Chemical Reaction How to Use Hess's Law to Calculate Enthalpy Changes Understand the Laws of Thermochemistry What Enthalpy Means in Science What Is an Exothermic Reaction? Learn About Enthalpy Change From Heat of Formation Worked Problems Thermochemistry Heat of Formation Table for Common Compounds Understanding Endothermic and Exothermic Reactions You Need to Understand the Difference Between Endergonic and Exergonic What Is a Double Displacement Reaction? Understand Le Chatelier's Principle in Chemistry Factors that Affect Chemical Reaction Rates Why the Formation of Ionic Compounds Is Exothermic See How to Calculate Enthalpy Change from a Sample Problem What Is Chemical Equilibrium? What Is Bond Energy?