Chapter 8, Problem 8.71P

A liquid is placed in a wcll-insulatcd container, which is then scaled. Initially, the container and its contents (the liquid and pure nitrogen) are at 93°C and 1 atm; the liquid volume is 70cm³, and the gas volume is 3.00 L. The liquid partially evaporates, and the system cools down and eventually comes to thermal equilibrium at 85°C with liquid still present. Physical property data for the liquid and its vapor are:

   $\begin{array}{l}\Delta {\hat{U}}_v=20kcal/molat90°C\\ {\left(C_p\right)}_{liq}=20cal/mol\cdot °C\\ {\left(C_p\right)}_{vap}=10cal/\left(mol\cdot °C\right)\\ {\left(SG\right)}_{liq}=0.90\\ MW=42\end{array}$

Determine ${\left(C_v\right)}_{liq}$and ${\left(C_v\right)}_{vap}$

1. (See Equations 8.3-11 and 8.3-12.)
2. Draw and label a flowchart for this closed system process, and write and simplify the energy balance equation, assuming adiabatic operation.

Use the energy balance to calculate the mass of liquid that evaporates, taking 4.97 cal/(mol·°C) as the heat capacity of nitrogen.

Calculate the vapor pressure of the liquid at 85°C, assuming that the gas volume remains constant at 3.00 L.