Thermodynamics

Laws of Thermodynamics

• Zeroth Law of Thermodynamics ("You have to play the game.")
• If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with each other
• Two bodies are in thermal equilibrium if there is no net flow of thermal energy between them when they are in thermal contact
• First Law of Thermodynamics ("You can't win.")
• In a closed system, $\triangle U = Q - W$
• $\triangle U$: Change in the internal energy
• $Q$: Amount of heat supplied to the system
• $W$: Amount of work done by the system on its surroundings
• Second Law of Thermodynamics ("You can't break even.")
• In a natural thermodynamic process, the sum of the entropies of the interacting thermodynamic systems increases.
• Maxwell's demon does not violate the second law
• Third Law of Thermodynamics ("You can't even quit the game.")
• The entropy of a system approaches a constant value as the temperature approaches absolute zero.

Work Done by Gas

• $W = \int_{V_1}^{V_2} P dV$
• Work done = Area under the curve in a $P$-$V$ graph

Thermodynamics Processes of Ideal Gas

• Isobaric Process
• $\triangle P=0$
• Isochoric Process (Isovolumetric Process)
• $\triangle V=0$, thus $W=0$
• Isothermal Process
• $\triangle T=0$; $\triangle U=0$
• $PV$ ($=nRT$) remains constant
• Adiabatic Process
• $Q=0$