Answer to Question #226646 in Physics for Zee

Question

Oxygen (molar mass 32 kg/kmol) expands reversibly in a cylinder behind a piston at a constant pressure of 3.161 bar. The volume initially is 0.0128 m³ and finally is 0.0313 m³ , the initial temperature is 17 ⁰C. Calculate the work input during the expansion with the correct unit. Assume oxygen to be a perfect gas and take the specific heat at constant pressure as = 0.917kj/kgK.

Answer 1

$V_1/T_1=V_2/T_2\to T_2=T_1V_2/V_1=290\cdot0.0313/0.0128=709.14\ (K)$

$w=W/m\to W=mR\Delta T/\mu+mc_V\Delta T=m\Delta T(R/\mu+c_V)=c_pm\Delta T$

So, we have $w=c_p\Delta T=917\cdot(709.14-290)=384 \ 351\ (J/kg)$ . Answer