A gas is a form of matter that fills any container it occupies.
2. An equation of state interrelates pressure, volume,
temperature, and amount of substance: p = f(T,V,n).
3. The pressure is the force divided by the area to which the force
is applied. The standard pressure is p7 = 1 bar (105 Pa).
4. Mechanical equilibrium is the condition of equality of
pressure on either side of a movable wall.
5. Temperature is the property that indicates the direction of the
flow of energy through a thermally conducting, rigid wall.
6. A diathermic boundary is a boundary that permits the passage
of energy as heat. An adiabatic boundary is a boundary that
prevents the passage of energy as heat.
7. Thermal equilibrium is a condition in which no change of
state occurs when two objects A and B are in contact through
a diathermic boundary.
8. The Zeroth Law of thermodynamics states that, if A is in
thermal equilibrium with B, and B is in thermal equilibrium
with C, then C is also in thermal equilibrium with A.
9. The Celsius and thermodynamic temperature scales are
related by T/K = θ/°C + 273.15.
10. A perfect gas obeys the perfect gas equation, pV = nRT, exactly
under all conditions.
11. Dalton’s law states that the pressure exerted by a mixture of
gases is the sum of the partial pressures of the gases.
12. The partial pressure of any gas is defined as pJ = xJp, where
xJ = nJ/n is its mole fraction in a mixture and p is the total
13. In real gases, molecular interactions affect the equation of
state; the true equation of state is expressed in terms of virial
coefficients B, C, . . . : pVm = RT(1 + B/Vm + C/V2m
+ · · · ).
14. The vapour pressure is the pressure of a vapour in equilibrium
with its condensed phase.
15. The critical point is the point at which the volumes at each
end of the horizontal part of the isotherm have merged to
a single point. The critical constants pc, Vc, and Tc are the
pressure, molar volume, and temperature, respectively, at the
16. A supercritical fluid is a dense fluid phase above its critical
temperature and pressure.
17. The van der Waals equation of state is an approximation to
the true equation of state in which attractions are represented
by a parameter a and repulsions are represented by a
parameter b: p = nRT/(V− nb) − a(n/V)2.
18. A reduced variable is the actual variable divided by the
corresponding critical constant.
19. According to the principle of corresponding states, real gases
at the same reduced volume and reduced temperature exert
the same reduced pressure.