Energy for Life
What Are the Laws of Thermodynamics?
The Laws of Thermodynamics
The study of energyglossary term (opens in a new window) is called thermodynamicsglossary term (opens in a new window). A scientific understanding of thermodynamics has resulted in three basic laws.
The first law of thermodynamics is related to the conservation of energy and is often called the Law of Conservation of Energy. The law states that energy cannot be created or destroyed. The total energy in the universe remains constant. Energy can, however, be transformed from one form into another.
For example, when an organism respires glucose molecules, some of the chemical potential energyglossary term (opens in a new window) of the glucose molecules is transformed into the chemical potential energy of other molecules such as ATP, some into other compounds, and some into thermal energyglossary term (opens in a new window). No energy disappears. The amount of energy at the beginning is the same as at the end.
The second law of thermodynamics states that the entropy of a system cannot decrease. Entropy is the measure of disorder, or chaos, in a system. Systems increase in disorder until equilibrium is reached. This law of thermodynamics explains why energy cannot be transferred from a colder body to a hotter body and why energy conversions are never 100% efficient. Most of the energy taken in from food is lost as thermal energy. Only a small percent of the energy taken in is used to do work. This thermal energy is why people feel hot when exercising. The conversion of potential energy to kinetic energy releases a lot of thermal energy.
The third law of thermodynamics defines the point at which the thermal energy of molecules is zero. This point is called absolute zero and is defined as 0K (Kelvin); this occurs at -273°C. Absolute zero is the lowest possible temperature because atoms have ceased moving.
It is important to understand that the laws of thermodynamics apply to closed systems. A closed system is one which no energy can enter or leave. The ultimate closed system is the universe. In nature all systems are open—energy can get in or out. Organisms are open systems within the bigger closed system of the universe. The Laws of Thermodynamics apply to them just as they do to the rest of the universe.
