### Table 8.3

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**Sat Feb 10, 2018 8:14 pm**Question 8.67 asked us to use tables 3, 6, and 7. For part A, we have to find the enthalpy of formation of H20, and we do this using bond enthalpies which are found in tables 6 and 7. However, this only gives us the enthalpy of water in the gas form. Therefore we have to use the formula ∆Hvap = H(vapor) - H(liquid). In table 3, there are two different values for the ∆Hvap of water: 40.7 and 44.0 at 25 degrees Celsius. I used the one that is on our constants and equations sheet which is ∆Hvap = 40.7 kJ.mol-1. However, my answer was slightly off because the answer was solved for by using 44.0. How do we know which one to use when the question does not give us the temperature?