Question

PROBLEM-1 (10%) Why is “generalized compressibility chart” used? Explain the purpose. PROBLEM-2 (10%) Explain the difference between R and Ru. How are these two related?

Answer 1

1. Generalized compressibility chart shows PVT relation of gases and is used to find out the compressibility factor (z) which is plotted against the reduced pressure P_R & the reduced temperature T_R.

compressibility factor (z) = P $\bar{V}$ /RT

also, reduced pressure P_R = P/P_c & reduced temperature T_R = T/T_c

for Z=1 , the gas is behaving as ideal gas. As behaviour of gases, depends on the value of compressibility factor. And is usefully thermodynamic property for modifying the ideal gas law to account for the real gas behaviour.

2. DIFFERENCE BETWEEN R & R_u

R = specific gas constant, different for different gases, depends on the molecular weight of the gas

R_u = universal gas constant, (i.e, 8.314 J/mol-K or 1.985 Cal / mol-K)

RELATION BETWEEN R & R_u

R = R_u / M

where, M = molecular weight of the gas