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Entropy can be viewed as a measure of molecular disorder, or molecular randomness is
a property designated S and is defined as
dS =(δQ/T) int

Environment refers to the region beyond the immediate surroundings whose properties
are not affected by the process at any point.

Equation of state is any equation that relates the pressure, temperature, and specific
volume of a substance. Property relations that involve other properties of a substance at
equilibrium states are also referred to as equations of state.

Equilibrium implies a state of balance. In an equilibrium state there are no unbalanced
potentials (or driving forces) within the system. A system in equilibrium experiences no
changes when it is isolated from its surroundings.

First law of thermodynamics is simply a statement of the conservation of energy
principle; it may be expressed as follows: Energy can be neither created nor destroyed;
it can only change forms. The net change (increase or decrease) in the total energy of
the system during a process is equal to the difference between the total energy entering
and the total energy leaving the system during that process. The energy balance can be
written explicitly as
E in - E out =(Q in -Q out ) + (W in -W out ) + (E mass, in- E mass, out ) = ∆E system
First law of thermodynamics for a closed system using the classical thermodynamics
sign convention is
Q net, in - W net, out = ∆E system or Q - W =∆E,
where Q = Q net, in = Q in - Q out is the net heat input and W = W net, out = W out - W in
is the net work output. Obtaining a negative quantity for Q or W simply means that
the assumed direction for that quantity is wrong and should be reversed.

Gage pressure is the difference between the absolute pressure and the local atmospheric
pressure.

Gas constant R is different for each gas and is determined from R = R μ/μ.

Heat engines are devices designed for the purpose of converting other forms of energy
(usually in the form of heat) to work. Heat engines differ considerably from one
another, but all can be characterized by the following:
1. They receive heat from a high-temperature source (solar energy, oil furnace, nuclear
reactor, etc).
2. They convert part of this heat to work (usually in the form of a rotating shaft).
3. They reject the remaining waste heat to a low-temperature sink (the atmosphere,
rivers, etc.).
4. They operate on a cycle.

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