Laws of Thermodynamics & Environmental Systems (SL IB Environmental Systems & Societies (ESS))

• Energy exists in many different forms, including light energy, heat energy, chemical energy, electrical energy, and kinetic energy
• The way in which energy behaves within systems can be explained by the laws of thermodynamics
  • There are two laws of thermodynamics

• The first law of thermodynamics is as follows:

Energy can neither be created nor destroyed, it can only be transformed from one form to another

• This is also known as the principle of conservation of energy
  • It means that the energy entering a system equals the energy leaving it

• The transfer of energy in food chains within ecosystems demonstrates the principle of conservation of energy
  • Energy enters the system (the food chain or food web) in the form of sunlight
  • Producers convert this light energy into biomass (stored chemical energy) via photosynthesis
  • This chemical energy is passed along the food chain, via consumers, as biomass
  • All energy ultimately leaves the food chain, food web or ecosystem as heat energy

• 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 is 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

• The second law of thermodynamics explains the decrease in available energy within ecosystems
  • In a food chain, for example, energy is transformed from a more concentrated (ordered) form (e.g. light energy the Sun), into a more dispersed (disordered) form (heat energy)
  • Initially, light energy from the Sun is absorbed by producers
  • However, even at this initial stage, energy absorption and transfer by producers is inefficient due to reflection, transmission (light passing through leaves) and inefficient energy transfer during photosynthesis
  • The energy that is converted to plant biomass is then inefficiently transferred along the food chain through respiration and production of waste heat energy
  • As a result of these inefficient energy transfers, food chains are often short (they rarely contain more than five trophic levels)

The laws of thermodynamics - energy cannot be created or destroyed (it can only be transformed), and energy is always lost from systems when work is done, bringing about disorder (increasing entropy)