Print Calculator -d Periodic Table Question 3 of 10 Map General Chemistry 4th Ed

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Print Calculator -d Periodic Table Question 3 of 10 Map General Chemistry 4th Edition . iversity Science Books presented by Sapling Learning CompoundAG(kJ/mol) Use the data given here to calculate the values of Gmn at 25 for the reaction described by the equation +387.7 -538.4 +402.0 A B Number 4G kJ If AHxn and ASn are both positive values, what drives the spontaneous reaction and in what direction at standard conditions? The spontaneous reaction is O O O O enthalpy-driven to the right. entropy-driven to the right. entropy-driven to the left. enthalpy-driven to the left. Previous Check Answer Next Exit Hint

Explanation / Answer

a)

dGRxn = Gproducts - Greactants

dGRxn = G-C - (G-A + G-B)

dGRxn = 402 - (387.7 - 538.4 )

dGrxn = 552.7 kJ

Q2.

if DH and dS are positive

In order to compare equilibirum vs. spontaneous/nonspontaneous reactions, we better use a criteria.

Recall that if dSuniverse > 0, this is spontaneous, if dSuniverse = 0, this is inequilbirium and if dSuniverse < 0 this is never possible.

Then, recall that

dSuniverse = dSsurroundings + dSsystem

dSsystem = Sproducts - Sreactants

dSsurroundings = Qsurroundings/T = -dHsystem/T

therefore

dSystem =  -dHsystem/T + dSsystem

If we multiply by -T

dGrxn = dHrxn - T*dSrxn

Now, analysis of dG value... which is the "free energy" available for a process to follow

if dG <0 , this will be spontaneous

if dG = 0 , this is in equilibrium

if dG > 0, this will not be spontaneous

Now...

dG = dH - T*dS

Possible values are, dH = +/- and dS = +/-; T is always positive ( absolute value)

Analysis of cases:

Case 3.

if dH is positive (+) and dS is positive (+) --> dG = dH - T*dS --> analysis must be done

if T is very low... then dH > T*dS; then this will be Positive value in dG; i.e. not spontaneous

if T is very high... then  dH < T*dS; then this will be Negative value in dG; i.e. spontaneous

therefore...

Entropy driven only, to the right

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