Calculate the values of the molar heat capacities Cv and Cp of a gas,if the ratio of the heat capacities is 1.33.What is the atomicity of the gas?Given R=8.31J/mol-k.

2 Answers
Jun 8, 2018
  • ("C"_"p")/("C"_"v") = gammaCpCv=γ
  • "C"_"p" - "C"_"v" = "R"CpCv=R

From above two equations

"C"_"p" = ("R" gamma)/(gamma - 1)Cp=Rγγ1

color(white)("C"_"p") = "8.314 × 1.33"/(1.33 - 1)Cp=8.314 × 1.331.331

color(white)("C"_"p") = "33.5 J/mol K"Cp=33.5 J/mol K

"C"_"v" = "C"_"p"/gammaCv=Cpγ

color(white)("C"_"v") = "33.5 J/mol K"/"1.33"Cv=33.5 J/mol K1.33

color(white)("C"_"v") = "25.2 J/mol K"Cv=25.2 J/mol K

gammaγ is 1.331.33 therefore it’s triatomic (Atomicity= 3=3) gas.

underline(bb"Type of gas" color(white)(............) bb(gamma)color(white)(....))
"Monoatomic" color(white)(000=) 1.66
"Diatomic" color(white)(..............) 1.40
"Triatomic" color(white)(......!!!!!!) 1.33

Jun 8, 2018

See below

Explanation:

Generally:

c_p - c_v = R

Here:

c_p/c_v = 4/3

implies c_v = 3R, qquad c_p = 4R

We know:

  • c_p/c_v = (5 R + 2X)/(3 R + 2X)

  • X = {(0 qquad qquad "monatomic"),(R qquad qquad "diatomic"),(3/2 R qquad qquad "polyatomic"):}

4/3 = 8/6 = (5 + 2 * 3/2)/(3 + 3 * 3/2)

Polyatomic