Entropy of Systems (HL) (HL IB ESS OLD COURSE - IGNORE)
Revision Note
Written by: Alistair Marjot
Reviewed by: Bridgette Barrett
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
Examiner Tips and Tricks
Remember that the second law of thermodynamics is about energy loss and increased entropy, not energy destruction (energy is always conserved, but it becomes less useful).
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