First law
.
Statement. Change in internal energy = heat added + work done ON system.
Cambridge sign convention.
- : heat added TO system.
- : work done ON system.
Energy conservation. Any change in must come from heat or work.
Common processes.
- Isothermal: constant → (ideal gas) → .
- Adiabatic: → .
- Constant volume: → .
- Constant pressure: .
Example. Gas absorbs 200 J heat, work 80 J done on it: J.
Cambridge tip. State sign convention explicitly.
- .
- Sign convention clear.
- Process types.
See the full worked example for the first law of thermodynamics →