Without computing the actual value of the entropy change, predict its sign for the following reactions. Begin by balancing the equation for each, paying close attention to the phases that are stable at T = 298K and 1.00 bar of pressure?

a) The formation of Acetone (C3H6O(l))
b) The combustion of ammonium oxalate C2H8N2O4
c) The reaction between a Lead(IV) nitrate solution and a sodium sulfate solution.

1 Answer
anor277
Feb 22, 2018

#3C(s) + 3H_2(g) + 1/2O_2(g) rarr H_3C-C(=O)CH_3(l)#

#DeltaS_"rxn"^@# should be negative.....

Explanation:

Why? Well, we are going from gaseous reactants to liquid products...the which should represent a DECREASE in disorder...

#(NH_4)_2C_2O_4(s) +4O_2(g)rarr 2CO_2(g) +4H_2O(l)+2NO_2(g)#

Is it balanced? You tell me....? Anyway,
#DeltaS_"rxn"^@# should be marginally positive.....given that you are making 4 moles of gaseous product, whose statistical probability for disorder should be large in magnitude (the entropy of a gaseous triatom should be LARGER than a gaseous diatom).

#2Na_2SO_4(aq) + Pb(NO_3)_4(aq) rarrPb(SO_4)_2(s)darr +4NaNO_3#..

They should not be asking you this one. Because this is not a question that they have demonstrated in an undergraduate laboratory. Plumbic sulfate is PROBABLY insoluble (plumbous sulfate certainly is)...because there are more reactant solute particles, #DeltaS_"rxn"^@# should be negative.

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