First Law of Thermodynamics
This simply states that energy cannot be created nor destroyed but can only be converted from one form to another.
- ΔU = ΔW + ΔQ
- where
- ΔU = change in total internal energy
- ΔW = work done
- ΔQ = total heat supplied
- ΔW = work done
Many equivalent statements are possible, including:
- Internal energy changes depend only on the initial and final states of the system, not on the path taken.
- The work done during an adiabatic process depends only on the initial and final states of the system, and not on the path taken.
- The internal energy change for any cyclic process is zero.
- Energy may change its form, but it cannot be created nor destroyed.
- When work is transformed into heat, or heat into work, the quantity of work is mechanically equivalent to the quantity of heat.
- The heat entering a system is equal to the increase in energy of the system plus the external work done by the system during the entry.
Historical Notes
Julius Robert von Mayer and James Joule shared the credit for the discovery of the universal law of conservation of energy, or the first law of thermodynamics.
- 1842 Mayer published an article on heat and energy. Joule made the same discovery while working independently.
See also: Energy, Heat, Joule, James Prescott, Mayer, Julius Robert von, Second Law of Thermodynamics, Third Law of Thermodynamics, Zeroth Law of Thermodynamics.
Subjects: Thermodynamics