Question 6.8: Calculating the Heat of Phase Transition from Standard Entha...
Calculating the Heat of Phase Transition from Standard Enthalpies of Formation
Use values of \Delta H_f^{\circ} to calculate the heat of vaporization, \Delta H_{\text {vap }}^{\circ}, of carbon disulfide at 25°C. The vaporization process is
CS_2(l) → CS_2(g)PROBLEM STRATEGY
The vaporization process can be treated like a chemical reaction, with CS_2(l ) the “reactant” and CS_2(g) the “product.” It is convenient to record the values of \Delta H_f^{\circ} under the formulas in the equation, multiplying them by the coefficients in the equation. You calculate \Delta H_{\text {vap }}^{\circ} by subtracting values for the “reactant” from values for the “product.”
Here is the equation for the vaporization, with values of \Delta H_f^{\circ} multiplied by coefficients (here, all 1’s).
\underset{1(89.7)}{CS_2(l)} \longrightarrow \underset{1(116.9) (kJ)}{CS_2(g)}The calculation is
