First Law Of Thermodynamics - Statement

The first law of thermodynamics states that the energy can neither be created nor destroyed, but can be converted from one form to another. This takes place with the interaction of heat, work, and internal energy.

The mathematical representation of the first law of thermodynamics is:

ΔU = Q + W

Where,

  • ΔU is the total change in the internal energy of the system
  • Q is the heat exchanged between the system and its surroundings
  • W is the work done either by the system or on the system

Below is the table explaining the sign conventions for heat, internal energy, and work done:

ΔU

Q

W

It will be positive if the temperature increases

It will be positive if heat enters the gas

It will be positive if the gas is compressed

It will be negative if the temperature decreases

It will be negative if heat leaves the gas

It will be negative if the gas expands

It will be zero if the temperature is constant

It will be zero if no heat is exchanged

It will be zero if the volume is constant

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