A chemical reaction happens when two different elements or substances interact to form a new substance with a different chemical composition. Along with every chemical reaction, comes a change in energy, where that energy is either gained or lost. Energy is the capacity of an object to do work or supply heat. Within the chemical bonds of substances there is chemical potential energy. The way atoms are arranged within a substance determines the amount of chemical potential energy a substance has. When a substance undergoes a chemical change, its energy changes. This change in energy can be observed in different ways. Oftentimes, a change in energy also results in a change of heat, with the heat flowing from a warmer object to a cooler one. Sometimes a change of energy, during chemical changes, causes a release of light or sound as well as well. For example the chemicals in fireworks produce light and sound.

A chemical change that gains energy is called an endothermic reaction. An endothermic reaction happens when an object absorbs heat from its surroundings during a chemical reaction. An example of an endothermic reaction would be melting ice. The ice absorbs heat, causing it to liquefy and taking away heat and energy from its surroundings.

There are also chemical reactions that release energy and heat, called exothermic reactions. Heat flows from the object into its surroundings, the opposite of an endothermic reaction. An example of an exothermic reaction is taking two substances, such as water and calcium chloride, and mixing them together, resulting in them releasing heat into the surrounding area.

During chemical reactions, though energy within an object is lost or gained, no new energy is actually created or destroyed. This is the law of conservation of energy. This means that if, during a reaction, an object loses a certain amount of energy or heat, its surroundings’ energy or heat will increase by that amount and vice versa.

It is important to know about energy within chemical reactions, because how energy changes during a chemical change, allows us to learn important things about the reaction that has taken place. A change in heat or energy allows us to know when a chemical change has taken place, whether or not it is endothermic or exothermic, and how much energy has been lost or gained within an object, all important when trying to understand how different chemicals react with one another. Changes in heat are also utilized in daily life. For example, when you burn wood, it releases heat, used to warm or light a space.

Understanding how different reactions release heat can allow us to further utilize energy changes in this way.