Why does exothermic

The chemical energy decreases, and the heat energy increases total energy is conserved. We need to look in a bit more detail to understand why heat energy is produced from chemical energy during an exothermic reaction:. Any reaction requires the necessary bonds in the reactants to be broken - this requires energy to be supplied, so heat energy is taken in. We call this amount of energy the Activation Energy for the reaction.

Once the necessary bonds have been broken, the new bonds between the atoms in the products can be formed. Why do exothermic reactions release heat? Those that require heat to occur are described as endothermic, and those that release heat as exothermic. Although we are generally quite familiar with endothermic phase changes, we are probably even more familiar with exothermic chemical reactions: Almost everyone has experienced the warmth of a fireplace or campfire. Burning wood provides heat through the exothermic chemical reaction of oxygen O with cellulose C 6 H 10 O 5 , the major chemical component of wood, to produce carbon dioxide CO 2 , steam H 2 O and heat.

In today's space age, probably everyone has seen a rocket launch on television or, if lucky, in person. What powers those rockets are highly exothermic chemical reactions. The great billows of white clouds seen behind launched rockets are really the product gases dispersing the white aluminum oxide powder. Where is the exothermic heat energy coming from? The heat comes from the energy stored in the chemical bonds of the reactant molecules--which is greater than the energy stored in the chemical bonds of product molecules.

In endothermic chemical reactions, the situation is reversed: more chemical energy is stored in the bonds of the product molecules than in the bonds of the reactant molecules. Already a subscriber? Sign in. This particular resource used the following sources:.

Skip to main content. Search for:. Exothermic and Endothermic Processes. Learning Objective Distinguish between endothermic and exothermic reactions. Key Points All chemical reactions involve the transfer of energy. Endothermic processes require an input of energy to proceed and are signified by a positive change in enthalpy. What is the value of K c? For the previous equation, does the equilibrium favor the products or the reactants?

Is this an exothermic or endothermic reaction? Because the K value decreases with an increase in temperature, the reaction is an exothermic reaction. In the initial reaction, the energy given off is negative and thus the reaction is exothermic.