12:47 AM
M V Rao
IDEAL AND REAL GASES AND THERMODYNAMIC
RELATIONS
1. Define Ideal gas.
It is defined as a gas having no forces of intermolecular attraction. These gases will follow the gas laws at all ranges of pressures and temperatures.
2. Define Real gas.
It is defined, as a gas having the forces of attraction between molecules tends to be very small at reduced pressures and elevated temperatures.
3. What is equation of state?
The relation between the independent properties such as pressure, specific volume and temperature for a pure substance is known as the equation of state.
4. State Boyle’s law.
It states that volume of a given mass of a perfect gas varies inversely as the absolute pressure when temperature is constant.
5. State Charle’s law.
It states that if any gas is heated at constant pressure, its volume changes directly as its absolute temperature.
6. Explain the construction and give the use of generalized compressibility chart.
The general compressibility chart is plotted with Z versus Pr for various values of Tr. This is constructed by plotting the known data of one of mole gases and can be used for any gas. This chart gives best results for the regions well removed from the critical state for all gases.
7. What do you mean by reduced properties?
The ratios of pressure, temperature and specific volume of a real gas to the corresponding critical values are called the reduced properties.
8. Explain law of corresponding states.
If any two gases have equal values of reduced pressure and reduced temperature, then they have same values of reduced volume.
9. Explain Dalton’s law of partial pressure.
The pressure of a mixture of gases is equal to the sum of the partial pressures of the constituents. The partial pressure of each constituent is that pressure which the gas would expect if it occupied alone that volume occupied by the mixtures at the same temperatures.
m = mA+mB+mC+……. = _mi
mi = mass of the constituent.
P = PA+PB+PC+……. = _Pi,
Pi = the partial pressure of a constituent.
10. State Avogadro’s Law.
The number of moles of any gas is proportional to the volume of gas at a given pressure and temperature.
11. What is Joule-Thomson coefficient?
The temperature behaviors of a fluid during a throttling (h = constant) process is described by the Joule-Thomson coefficient defined as:
µ =[dT/dP]n
12. What is compressibility factor?
The gas equation for an ideal gas is given by (PV/RT) = 1, for real gas (PV/RT) is not equal to 1 (PV/RT) = Z for real gas is called the compressibility factor.
13. What is partial pressure?
The partial pressure of each constituent is that pressure which the gas would exert if it occupied alone that volume occupied by the mixtures at the same temperature.
14. Define Dalton’s law of partial pressure.
The total pressure exerted in a closed vessel containing a number of gases is equal to the sum of the pressures of each gas and the volume of each gas equal to the volume of the vessel.
15. How does the Vander Waal’s equation differ from the ideal gas equation of state?
The ideal gas equation pV = mRT has two important assumptions,
1. There is little or no attraction between the molecules of the gas.
2. That the volume occupied by the molecules themselves is negligibly small
compared to the volume of the gas. This equation holds good for low
pressure and high temperature ranges as the intermolecular attraction and
the volume of the molecules are not of much significance.
As the pressure increases, the inter molecular forces of attraction and repulsion
increases and the volume of the molecules are not negligible. The real gas deviate considerably from the ideal gas equation
[p+(a/V2)](V-b) = RT
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