엥겔의 물리화학 3판 ch4.doc

Chapter 4: Thermochemistry
Problem numbers in italics indicate that the solution is included in the Student’s Solutions Manual
Questions on Concepts

Q4.1) Under what conditions are H and U for a reaction involving gases and/or liquids or solids identical

H = U + (PV). H U for reactions involving only liquids or solids because, to a good approximation, the volume does not change as a result of the reaction. If gases are involved, (PV) = nRT. Therefore, H U if the number of moles of reactants and products that are gases are the same.

Q4.2) If for the chemical compounds involved in a reaction are available at a given temperature, how can the reaction enthalpy be calculated at another temperature

The reaction enthalpy can be calculated to high accuracy at another temperature only if the heat capacities of all reactants and products are known using If the heat capacities of reactants and products are similar, the reaction enth…(생략)

Q4.3) Does the enthalpy of formation of compounds containing a certain element change if the enthalpy of formation of the element under standard state conditions is set equal to 100 kJ mol1 rather than to zero If it changes, how will it change for the compound AnBm if the formation enthalpy of element A is set equal to 100 kJ mol1

Q4.4) Is the enthalpy for breaking the first CH bond in methane equal to the average CH bond enthalpy in this molecule Explain your answer.

Q4.5) Why is it valid to add the enthalpies of any sequence of reactions to obtain the enthal