The standard heat of combustion of liquid n-octane to form CO₂ and liquid water at 25°C and 1 atm is ΔĤ_c = 5471 kJ/mol.

(a) Briefly explain what that means. Your explanation may take the form “When ______ (specify quantities of reactant species and their physical states) react to form ______ (quantities of product species and their physical states), the change in enthalpy is ______.”

(b) Is the reaction exothermic or endothermic at 25°C? Would you have to heat or cool the reactor to keep the temperature constant? What would the temperature do if the reactor ran adiabatically? What can you infer about the energy required to break the molecular bonds of the reactants and that released when the product bonds form?

(c) If 25.0 mol/s of liquid octane is consumed and the reactants and products are all at 25°C, estimate the required rate of heat input or output (state which) in kilowatts, assuming that Q̇ = ΔḢ for the process. What have you also assumed about the reactor pressure in your calculation? You don’t have to assume that it equals 1 atm.

(d) The standard heat of combustion of n-octane vapor is ΔĤ_c = 5528 kJ/mol. What is the physical significance of the 57 kJ/mol difference between this heat of combustion and the one given previously?

(e) The value of ΔĤ_c given in Part (d) applies to n-octane vapor at 25°C and 1 atm, and yet the normal boiling point of n-octane is 125.5°C. Can n-octane exist as a vapor at 25°C and a total pressure of 1 atm? Explain your answer.