How is Hess's law used to calculate the enthalpy of a reaction? O A. The desired enthalpy is obtained through adding intermediate
reactions together.
B. Enthalpies from similar equations are substituted for unknown
reaction enthalpies.
C. The enthalpy is obtained from the difference in final and initial
reactions in a path.
D. The final equation in a reaction path provides the enthalpy for the
desired reaction.

Hess's law derives directly from the law of conservation of energy, as well as its expression in the first law of thermodynamics. By Hess's law, the net change in enthalpy of the overall reaction is equal to the sum of the changes in enthalpy for each intermediate transformation: ΔH = ΔH1+ΔH2+ΔH3.

Explanation:

answer : (a) volume of the gas = 8.67 ×   l

                (b) second virial coefficient b = -1.21226 l/mole

solution :   given,     t = 300k

                                p = 20atm

                                z = 0.86

                                n = 8.2 mmoles = 8.2 × moles

                                r =   0.082 l atm/k/mol

        find,     (a) volume of gas   and (b) second virial coefficient b at 300k.

formula used :            

                          and            

(a)            

                    = \times 0.082\times 300}{20}[/tex]

                    = 8.67 ×   l

(b)      

                    = (0.00867-1) × 8.659

                    = - 8.5839 l/mole