Topscore Free ENERGY Problem..Please help!

[AZDent]

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Ok - I understand this question, but the answer has an extra variable in it.

Given that standard enthalpy of formation for NO(g) is 90.25 kJ/mole, calculate the free energy of the rxn:

N2 + O2 > 2NO

It gives you all the absolute entropies: N2 = 192, NO = 211, O2 = 205.

Answer: 180.5 - (298)(25)(1 x 10^-3)

I know to find the change in entropy by doing products - reactants, then use free energy problem. I got the same, but don't know where the 1 x 10^-3 comes from???? HELP ME!

 

[tranv117]

Ok - I understand this question, but the answer has an extra variable in it.

Given that standard enthalpy of formation for NO(g) is 90.25 kJ/mole, calculate the free energy of the rxn:

N2 + O2 > 2NO

It gives you all the absolute entropies: N2 = 192, NO = 211, O2 = 205.

Answer: 180.5 - (298)(25)(1 x 10^-3)

I know to find the change in entropy by doing products - reactants, then use free energy problem. I got the same, but don't know where the 1 x 10^-3 comes from???? HELP ME!

are the entropies given in Joules or kJ?

 

[AZDent]

They are J.

 

[Taihenkoichi]

Well you just answered your own question.

If the units of enthalpy are in KJ/mol the units of entropy must be as well.
So 25 J/mol = (25)(1 x 10^-3 KJ/mol) = .025 KJ/mol

 

[tranv117]

yeps, its a conversion thing. I think i mentioned this before. The best tip when taking the DAT is to be calm and read the questions carefully. It's very easy to make careless mistakes and lose out on some points.

 

[AZDent]

DUH...ok, I think I may have over-studied at this point...back to basics and stop thinking so hard. Thx guys...

 

[keliao]

was deltaS given as 25J ?? because i dont see that .