1st law of thermodynamics

Answer Posted / azmi.2004

First Law of Thermodynamics

The first law of thermodynamics is the application of the
conservation of energy principle to heat and thermodynamic
processes:

The first law makes use of the key concepts of internal
energy, heat, and system work. It is used extensively in the
discussion of heat engines. The standard unit for all these
quantities would be the joule, although they are sometimes
expressed in calories or BTU.

It is typical for chemistry texts to write the first law as
ΔU=Q+W. It is the same law, of course - the thermodynamic
expression of the conservation of energy principle. It is
just that W is defined as the work done on the system
instead of work done by the system. In the context of
physics, the common scenario is one of adding heat to a
volume of gas and using the expansion of that gas to do
work, as in the pushing down of a piston in an internal
combustion engine. In the context of chemical reactions and
process, it may be more common to deal with situations where
work is done on the system rather than by it.

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