SI Chem 178
Chapter 19
Leader: Emily
4.9.2013
Recommended problems for recitation & quiz on Friday:
Chapter 19: 7 – 10, 56, 58, 59c, 61c, 63, 65, 66, 67, 72, 75, 78, 79, 82b, 83, 85
Review: (Ch 19)
Suniv= _________________________
Suniv for spontaneous processes is < OR > 0
What is Suniv for reversible processes? _____________
With this in mind, if I told you that Ssys for a reversible reaction was -87, what
could you conclude about the Ssurr?
If Ssurr was -65 for a spontaneous process, what could you conclude about the
Ssys?
What does isothermic mean? When do we use isothermic calculations? Which
equation do we use? What other info must we have?
________________, ___________________, and ____________________ are
all things that increase the number of microstates.
Conceptual Review of New Stuff:
T/ F Temperature and pressure must be constant when applying Gibbs Free
Energy concepts.
What are the two equations we can use to calculate G ?
If H is negative, what can we conclude about the reaction? Positive?
If G is large and negative, does the reaction proceed very quickly?
G is ______________ for spontaneous processes.
Elements in their standard state have a Gibbs Free Energy value (G) of _____
Ex: O2, H2, N2
When Q < K we have excess _______________. Which direction do we go?
When Q=K we are in a state of …? And our G = ?
Application Problems:
19.57 For a certain chemical rxn, H=-35.4 kJ and S=-85.5 J/K.
a. Is the reaction exothermic or endothermic?
b. Is there an increase or decrease in randomness/disorder in the reaction?
c. What is G for the reaction if it’s carried out at 298K
d. Is it spontaneous?
e. When both S and H are negative, what is/are the potential signs for G?
Are there constraints?
19.67 A constant-pressure reaction is spontaneous at 390K, the H=23.7 kJ.
What can you determine about S for the reaction?
19.69 For a particular reaction, H= -32 kJ and S=-98 J/K
a. At what temperature will the reaction have G=0? What does this mean?
b. If T is increased from that in part a., will the reaction be spontaneous or nonspontaneous?
19.72 Consider the following reaction that creates methanol from oxidizing
methane: CH4(g) + ½ O2(g)  CH3OH(g)
a. Calculate S and H using Appendix C
b. How do you expect G to vary with increasing T?
c. Calculate G at 298K. Is it spontaneous at this T?
d. Is there a temperature that creates equilibrium for the reaction that also
ensures stability?