Homework Help: 6 Entropy

Posted by Nicole on Tuesday, May 3, 2011 at 11:13pm.

Using the thermodynamic data provided below, calculate the standard change in entropy when one mole of sodium nitrate is dissolved in water?
S° (J/K•mol)
NaNO3(s) 116.3
Na+(aq) 60.25
NO3–(aq) 146.4
Using the value you calculated, how will the solubility of sodium nitrate change if the temperature of the system is increased?

a.Solubility will increase.
b.Solubility will decrease.
c.Solubility will not be affected by temperature changes.
d.Cannot determine with provided information.

6 Entropy - bobpursley, Wednesday, May 4, 2011 at 12:19am
NaNO3>>Na+ + NO3-
116.3=60.25+146.4

change in Entropy= sum produts- sum reactants.

so figure the change in entropy. Notice it is postitive, so it is becoming more disordered....

the term then in the gibbs free energy equation (TdeltaS gets bigger, but it is negative)..

GibbsFreeEnergy= changeEnthalpy- TdS

so the TdS term gives a larger negative free energy, so solubility will increase. Bigger negative Gibbs, more spontaneous.

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