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Identify the complete and correct statement of the first law of thermodynamics.
The first law of thermodynamics is a version of the law of conservation of energy, adapted for thermodynamic systems.
- The law of conservation of energy states that the total energy of an isolated system is constant.
- Energy can neither be created nor be destroyed but can be transformed from one form to another.
The first law is often formulated by stating that the change in the internal energy of a closed system is equal to the amount of heat supplied to the system, minus the amount of work done by the system on its surroundings
δQ = dU + δW
ΔU = δQ − δW
According to the First Law of thermodynamics, “For a closed system undergoing a cycle, net heat transfer is equal to network transfer.”
ΣQ = ΣW.
The heat added to the system has been considered to be a positive quantity.
Conversely, if heat were removed, then the heat would be a negative quantity.
Work done on the system = sign convention is -ve
Work done by the system = sign convention is +ve
Note that if no heat transfer occurs, the system is called adiabatic.
Work is also subject to a sign convention, which is work done by a system is positive work done on a system is negative
Heat or energy transfer to the system = sign convention is +ve
Heat or energy transfer from the system = sign convention is -ve