[dnbwise]

Consider the following rxn @ 298K: H2(g) + I2(s) <-> 2HI(g)

For the above eqn, circle the value for deltaH (in kJ)
33.6  42.1  51.8  69.3  74.6  80.8

For the above eqn, circle the value for deltaS (in J/K)
103.8  119.9  147.5  165.9  186  198.3

For the above eqn, circle the value for deltaG (in kJ)
2.4  7.8  11.2  13.9  15.5  16.1

I am given the following information to solve:
Standard deltaH for HI(g) = 25.9 kJ
Standard deltaS for H2(g) = 130.6 J/K, HI(g) = 206.33 J/K, I2(g) = 116.14 J/K

I was able to solve for deltaS and got 165.9 J/K, but from the information given I can't seem to get the correct answer for deltaH, which I need to find deltaG.

I used the eqn "T = deltaH/deltaS" to try to get the deltaH, but I got the wrong answer.

Thanks for any help.

[Yggdrasil]

The standard deltaH of a compound is defined as the production of one mole of a compound from the elements composing it.  Since the elemental form of hydrogen is H₂ and the elemental form of iodine is I₂, the reaction is essentially the same as the reaction with which the standard enthalpy of formation is calculated, except that you're forming two moles of HI instead of one.  Thus, the change in enthalpy is twice the standard enthalpy of formation of HI, 51.8.

[dnbwise]

wow, thanks alot. I guess I need to look at the definitions for these values instead of just solving problems. I'm used to just doing the math rather than really grasping all the details.