What is Energy ?
Energy
Energy is defined as the capacity to do work. Work is defined as the movement of a mass, or the product of the force and the distance through which the mass was moved. Like matter, energy is essentially neither created nor destroyed, but only converted from one form to another. Different forms of energy include mechanical, heat, light, electrical, chemical, and nuclear energy.
Energy comes can be classified as either potential energy, stored in one configuration of atoms or position of matter in space, or kinetic energy, which by virtue of its motion, such as that of a falling body, can do work.
Heat energy is measured in calories. One calorie is equal to the amount of heat required to raise the temperature of one gram of water one degree, from 14.50C to 15.50C. One Calorie = 1000 calories = 1 kilocalorie or Kcal. The energy values of foods are measured in Calories.
Atoms and molecules in all matter are in constant motion, bouncing off of each other with kinetic energy that varies with heat and other forces. Particles of solids are closely bound and have less kinetic energy than those of liquids, which in turn have less than those of gases.
For any chemical reaction to occur, energy available to do work, or free energy, must be present. If an input of energy is required, the reaction is called endergonic; if the energy supplied is in the form of heat, it is also referred to as endothermic. Other reactions occur spontaneously and free energy is released as an output; these reactions are called exergonic. If the energy is released in the form of heat, they are exothermic. The amount of energy that must be supplied to complete a reaction is called the activation energy. Energy stored in a chemical bond is released when the bond is broken.