Endothermic reactions occur when new molecules being made form more new bonds than those that are broken. The net result of these new bonds being made is that energy is absorbed from the surroundings to make these new bonds and the reaction has a decrease in temperature or gets cooler. "Endo-" means inside and "therm" means heat. So this term endothermic means heat energy is taken in and used in the making of the new bonds. Many processes can also be endothermic without being a chemical reaction. This means that heat energy is input into the system to cause a physical change.
1. A "cold pack" used in sports gets cold when the chemical inside mixes with the water bag and new bonds form causing a decrease in temperature.
2. Photosynthesis involves the input of the sun's energy into a chemical reaction to make food for plants.
3. Melting ice is an endothermic process in which thermal energy from the environment causes the molecules of solid water to vibrate fast enough to change to a liquid.
4. Mixing water and potassium chloride, a salt, results in a cooler solution.
5. Mixing citric acid within baking soda causes a decrease in temperature.