7.3: Second Law of Thermodynamics

The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. Each energy transfer results in a certain amount of energy that is lost—usually in the form of heat—that increases the disorder of the surroundings. This can also be demonstrated in a classic food web. Herbivores harvest chemical energy from plants and release heat and carbon dioxide into the environment. Carnivores harvest the chemical energy produced by herbivores—with only a fraction of it representing the original radiant energy from the sun—and also release heat energy with carbon dioxide into their surroundings. As a result, the heat energy and other metabolic by-products released at each stage of the food web have increased its entropy.

The Second Law of Thermodynamics

The Second Law of Thermodynamics states that entropy, or the amount of disorder in a system, increases each time energy is transferred or transformed. In every energy transfer, a certain amount of energy is lost in a form that is unusable—usually in the form of heat. This heat energy can temporarily increase the speed of molecules it encounters. As such, the more energy that a system loses to its surroundings, the less ordered and the more random it becomes.

Similar to the First Law of Thermodynamics, the Second Law of Thermodynamics can also be demonstrated within a classic food web. When primary producers, such as plants, receive energy from the sun and make food, a small amount is transformed into unusable heat energy and is released along with oxygen into the environment.

When primary consumers, like herbivores harvest chemical energy from plants, they also release a small amount of heat energy along with carbon dioxide during metabolism. Carnivores harvest the chemical energy produced by herbivores—with only a fraction of it representing the original radiant energy from the sun—and also release heat energy with carbon dioxide into their surroundings. Thus, the released heat energy and other metabolic by-products have increased the entropy within the food web.

The second law of thermodynamics can also be demonstrated within a classic food web. It states that entropy, the amount of disorder in a system, increases each time energy is transferred or transformed.

When primary producers receive energy from the sun and make food, a small amount is transformed into unusable heat energy, which is released along with oxygen into the environment.

While primary consumers are harvesting chemical energy from plants, they also release a small amount of heat energy along with carbon dioxide during metabolism.

Finally, at the predator level, only a fraction of the original energy harnessed from the sun is available to use. The released heat energy and other metabolic byproducts have now increased the system's entropy.