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First law of thermodynamics

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The 1st law of thermodyamics simply states that energy can be neither created nor destroyed (conservation of energy). Thus power generation processes and energy sources actually involve conversion of energy from one form to another, rather than creation of energy from nothing.

The first law can be modeled simply as: ∑W=∑Q

Implications[edit | edit source]

This has important implications in energy technologies. Burning a fuel creates energy by converting a high chemical energy substance (e.g. hydrocarbons) into low chemical energy substances (e.g. carbon dioxide and water). The energy changes form, to heat and mechanical energy, but is not created.

In contrast, a if a substance does not change form into a lower chemical energy state, then no energy can be extracted from it.

Most notably, water cannot be used as fuel as the possible outputs are either:

  • Water at a similar temperature and in the same phase, i.e. having the same energy state - in which case we are looking at a perpetual motion machine,W i.e. pseudoscience.
  • Water at a higher temperature or gaseous phase, in which case energy must have been used up to cause this change, rather than generated.
  • Hydrogen and oxygen, which are at a higher energy state than water (demonstrated clearly by the fact that energy is released when hydrogen burns to form water). Again, energy must have been used up to cause this change, rather than generated.

Examples[edit | edit source]

  • Automobile Engine: Chemical to Kinetic
  • Heat/Furnace: Chemical to Heat
  • Hydroelectric: Gravitational to Electrical
  • Solar: Optical to Electrical

1st Law Equation[edit | edit source]


  • ΔE= change in internal energy
  • ΔQ= change in heat
  • ΔW= change in work

Interwiki links[edit | edit source]