Question

Determine ΔS°rxn and ΔG°rxn at 298 K for each of the following reactions, and determine if...

Determine ΔS°rxn and ΔG°rxn at 298 K for each of the following reactions, and determine if it is spontaneous under these conditions.
a. Ca( s ) + Cl2 ( g ) produces CaCl2 ( s )

b. 2C2H6 ( g ) + 7O2 ( g ) produces 4CO2 ( g ) + 6H2O( l )

c. SrCl2 ( s ) produces Sr (2+) ( aq ) + 2Cl (1–) ( aq )

Homework Answers

Answer #1

Solution.

The values of ΔS°rxn and ΔG°rxn can be obtained by using the following equations:

a)

b) The calculations are similar:

c) The calculations are quite similar as well:

ΔHfo(Sr2+) = −545.8 kJ·mol−1

ΔHfo(Cl-) = −167.1 kJ·mol−1
ΔHfo(SrCl2) = -828.9 kJ·mol−1
ΔHrxno = -545.8+2(-167.1)-(-828.9) = -51.2 kJ;

So(Sr2+) = −32.6 J·mol−1·K-1

So(Cl-) = 56.5 J·mol−1·K-1
So(SrCl2) = 114.9 J·mol−1·K-1
ΔSrxno = -32.6+2(56.5)-114.9 = -34.5 J·K-1

ΔGrxno  = ΔHrxno - TΔSrxno  = -51200-298(-34.5) = -40.9 kJ.
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