The mechanism that drives the train down the track, following clouds of smoke behind it, involves both chemical and physical changes. Energy is released during the chemical reaction. When higher energy coal and oxygen gas combine to generate lower energy products, heat is produced.

The heat energy generated by this chemical is absorbed by water in the locomotive's boiler shift, vaporizing to greater energy steam; steam pushes on pistons of the engine. This causes the wheels to spin and the train to set off!

The energy derived from the initial components has been transformed into heat and work.

This interaction of matter and energy is extremely essential and has a huge influence on civilization.

Many common materials emit, absorb, or change the flow of energy on a daily basis. Natural gas and oil, for example, release energy that we use to cook our food, heat our houses, and power our cars. Fertilizers benefit crops.

Solar energy may be converted into food. Metal wires facilitate the transmission of electrical energy. Polymer fibers in winter clothes, for example, impede the transfer of heat energy away from the body.

The study of energy and its changes is known as thermodynamics, and three chapters in this book cover this important issue.

Each particle in a system possesses potential and kinetic energy, and the total of these energies is the system's internal energy, E (some sources use the symbol U).

When the reactants of a chemical system convert to products, the internal energy of the system changes. This distinction, E, is the difference between internal energy following the change (Efinal) and internal energy prior to the change.

(Greek delta) means “change (or difference) in” and is computed as the result of subtracting the beginning state from the end state As a result, E is the total amount of energy released by the system minus the initial amount:

• ΔE = Final − Initial = Products − Reactants

The attached picture depicts a typical chemical system—the contents of a flask, which are typically substances undergoing physical or chemical change.

The surrounds are the flask itself, the air around the flask, additional equipment, and perhaps the rest of the laboratory.

In theory, the rest of the universe is the surrounds, but in reality, we only consider the portions that are relevant to the system:

• a rainstorm in Central Asia or a methane blizzard on Neptune are unlikely to impact the contents of the flask, but the temperature and pressure of the lab may.

• As a result, the experimenter specifies the system and its surroundings.

Heat, often known as thermal energy (symbolized by q), is the energy transmitted as a result of a temperature differential between the system and its surroundings.

For example, heat energy is transported from hot coffee (system), because they are at a lower temperature, the cup, your hand, and the air (surroundings).

Heat is transmitted from a hot burner (environment) to an ice cube (system) due to the fact that the ice is at a lower temperature.

Work, the energy transmitted when an item is moved by a force, is involved in all other kinds of energy transmission.

When you (system) kick a football, energy is transmitted as labor because the kick's force propels the ball as well as air (surroundings). When you pump up a ball, you are transferring energy as effort, because the additional air (system) exerts a force on the ball's inner wall (surroundings) and causes it to travel outward.

The sum of the energy transmitted is the entire change in a system's internal energy, as a source of heat and/or as a source of labor:

• ΔE = q + w