Answer to Question #226657 in Molecular Physics | Thermodynamics for Zee

Question

Oxygen (molar mass 32 kg/kmol) expands reversibly in a cylinder behind a piston at a constant pressure of 3.163 bar. The volume initially is 0.0112 m³ and finally is 0,0323 m³ , the initial temperature is 17.6 ⁰C. Calculate the heat supplied during the expansion in the correct unit to two decimal places. Assume oxygen to be a perfect gas and take the specific heat at constant pressure as = 0.917kJ / kg K and molar gas constant as = 8.314 J / kmol K.

Answer 1

Solution.

$p \times V = n \times R \times T$

$n = \frac{p \times V}{R \times T}$

$n = \frac{3.163 \times 101325 \times 0.0112}{8.31 \times (17.6+273.14)} = 1.49 \ mol$

$\frac{V1}{T1} = \frac{V2}{T2}$

$T2 = \frac{T1 \times V2}{V1}$

T2 = 838.48 K

$Q = n \times Cp \times \Delta T$

$Q = 1.49 \times 0.917 \times 10^3 \times (838.48-290.74) = 748393.59 \ J = 748.39 \ kJ$

Answer:

Q = 748.39 kJ