Assume that H°rxn and S°rxn are independent of temperature.

Question

For the reaction

2Na(s) + 2H₂O(l)2NaOH(aq) + H₂(g)

H°_rxn = -368.6 kJ and S°_rxn = -15.3 J/K

The standard free energy change for the reaction of  1.64 moles of Na(s) at 255 K, 1 atm would be  ____ kJ.

This reaction is (reactant,product) ____  favored under standard conditions at 255 K.

Assume that H°_rxn and S°_rxn are independent of temperature.

Answer 1

Hi Ahmad E.,

The relationship you need to use to solve is (one of the) central one(s) of thermodynamics. It is:

ΔG = ΔH - TΔS

Just plug in your data, and calculate!

By the way, what that equation is saying to you is, that any reaction has a tendency to proceed (move to the right) based on BOTH the (net difference of the) energies of the particular bonds broken and formed (that's the H term) but ALSO on the probabilities of the particles coming together in each direction of the reaction, the latter effect of which is heightened exactly proportionally to the absolute temperature of the reaction (that's the T delta S term).

OK now?

And the last bit you need to use, is the number of moles of the reactant, relative to the coefficient in the reaction as written. That's a ratioing.

-- Cheers, -- Mr. d.