Entropy of Systems (HL) (HL IB Environmental Systems & Societies (ESS))

Entropy of Systems

The second law of thermodynamics

• The second law of thermodynamics is as follows:

The entropy of a system increases over time

• Entropy is a measure of the amount of disorder in a system

• As entropy increases (through inefficiencies in energy transformations) the energy available to do work decreases

  • This is because the transformation and transfer of energy in any system is never 100% efficient

• In other words, in any energy conversion, the amount of useable energy at the end of the process is always less than the amount of energy available at the start

Entropy within ecosystems

Energy loss and biomass in ecosystems

• Energy transfer in ecosystems is not 100% efficient

• When energy passes from one trophic level to the next, a significant amount is lost as heat

  • This energy loss increases the entropy of the system

• Biomass decrease: as energy moves up the food chain, there is less biomass available at each successive trophic level

• This is a result of the energy losses and increased entropy

Entropy and cellular respiration

• Cellular respiration is the process by which living organisms convert glucose and oxygen into energy, with carbon dioxide and water as by-products.

  • During respiration, energy is released as heat, which increases the entropy of the system

• Organisms maintain low entropy within their cells and bodies (high organisation) by using energy from food

  • But in doing so, they release heat and increase the entropy of the environment

• Net increase in entropy:

  • While organisms can maintain internal order (low entropy), the overall entropy of the system (including the surrounding environment) increases due to the energy lost as heat