2.Zeroth law and first law

Thermodynamics 3rd Semester

Zeroth Law

If two systems are each in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other

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First Law

Enegy cannot be created and it cannot be destroyed.

β€œWhen a system (closed) undergoes a thermodynamic cycle, sum of the net heat supplied to the system from its surroundings and the net work input to the system from its surroundings must equal zero”

Heat transfer in to the system
Work transfer in to the system

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  • Heat supplied to the system - POSITIVE
  • Work done by the system - POSITIVE
  • Heat rejected by the system - NEGATIVE
  • Work done on the system - NEGATIVE

- Corollary

  • The internal energy of a closed system remain unchanged if the system is isolated from its surrounding

if 𝐼𝑓 𝑄 = 0 π‘Žπ‘›π‘‘ π‘Š = 0 π‘‘β„Žπ‘’π‘›, βˆ†π‘ˆ = 0

- Corollary

  • For a cycle, the net work done by the system is equal to the net heat added to the system.

Energy balance for closed system:




Specific total energy

note

  • Transient state - Change with time
  • Steady state - No change with time
  • Heat and work depend on the path it followed. They are called β€œpath functions”.