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Spontaneous Reactions and Maximum Concentration

Calculate the maximum concentration (in M) of sulfide ions in a solution containing 0.181 M of lead ions. The Ksp for lead sulfide is 3.4 x 10-28.

a. 1.9 x 10-27
b. 9.4 x 10-28
c. 1.5 x 10-26
d. 3.0 x 10-25
e. 3.4 x 10-28

A reaction that is spontaneous ___________.

a. will proceed as written without outside intervention
b. will be very rapid as written
c. will occur very slowly
d. is also spontaneous in the reverse direction
e. has an equilibrium position that lies very far to the left

In a spontaneous process, __________.

a. the path between reactants and products is irreversible
b. the reverse process is also spontaneous
c. forward and reverse processes occur at the same rate
d. the reverse process occurs at a higher rate than the forward process
e. the path between reactants and products is reversible

Which of the following is a reversible process?

a. Melting of ice at 0°C and 1 atm
b.Freezing of water at -10°C and 1 atm
c.Evaporation of water at 25°C and 1 atm
d.Freezing of water at -25°C and 1 atm
e.Melting of ice at 25°C and 1 atm

Given the following table of thermodynamic data, determine the normal boiling point (in °C) of TiCl4.
Substance ΔHf° S°
TiCl4(g) -763.2 kJ/mol 354.9 J/mol-K
TiCl4(l) -804.2 221.9

a. 308.3
b. 41.0
c. 35.3
d. 273.3
e. 133.0

Which equation represents a reaction that is decreasing in entropy as the reaction proceeds?

a. H2O(l) H2O(g)
b. 2C(s) + O2(g) 2CO(g)
c. CaCO3(s) CaO(s) + CO2(g)
d. 2H2(g) + O2(g) 2H2O(l)
e. 2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)

For which one of the following reactions should the sign of ΔS be negative?

a. C(s) + O2(g) CO2(g)
b. H2O(l) H2O(g)
c. NH3Cl(s) HCl(g) + NH3(g)
d.2NaCl(s) + H2SO3(aq) 2HCl(g) + Na2SO4(s)
e.2SO2(g) + O2(g) 2SO3(g)

Consider a pure, crystalline solid being heated from absolute zero to some very high temperature. Which one of the following processes produces the greatest increase in the entropy of the substance?

a. Heating the liquid
b. Boiling the liquid
c. Heating the solid
d. Heating the gas
e. Melting the solid

Given the following table of thermodynamic data, determine the ΔS° (in J/mol-K) for the reaction:
C2H2(g) + 2 H2(g) C2H6(g).

Substance S°
C2H2(g) 200.8 J/mol-K
C2H4(g) 219.4
C2H6(g) 229.5
H2(g) 130.58

a. -111.98
b. -101.88
c. -232.46
d. +101.88
e. +111.98

Which species below has/have ΔG°f = 0?

a.Both Co(s) and H2(g)
b. HCo(PF3)4(g)
c. Co(s)
d. H2(g)
e. PF3(g)

Solution Preview

Question: Calculate the maximum concentration (in M) of sulfide ions in a solution containing 0.181 M of lead ions. The Ksp for lead sulfide is 3.4 x 10-28.

a. 1.9 x 10-27
b. 9.4 x 10-28
c. 1.5 x 10-26
d. 3.0 x 10-25
e. 3.4 x 10-28

Response: Lead sulfide is PbS. Therefore, we know that

Ksp = [Pb+2][S-2] = 3.4x10-28 = (0.181)[S-2]

Now, all you do is solve for [S-2] and you've got your answer!

Question: A reaction that is spontaneous ___________.

a. will proceed as written without outside intervention
b. will be very rapid as written
c. will occur very slowly
d. is also spontaneous in the reverse direction
e. has an equilibrium position that lies very far to the left

Response: Spontaneity has nothing to do with kinetics since spontaneity is a thermodynamic property; therefore, it has nothing to do with speed of the reaction. Likewise, if the reaction is spontaneous it will proceed in the forward direction as written, and not in the reverse direction. Spontaneous means that the reaction will just happen, without any reference to a time frame. The conversion of graphite to diamond is spontaneous, but it sure does take a lot of time!

Question: In a spontaneous process, __________.

a. the path between reactants and products is irreversible
b. the reverse process is also spontaneous
c. forward and reverse processes occur at the same rate
d. the reverse process occurs at a higher rate than the forward process
e. the path between reactants and products is reversible

Response: If a process is spontaneous, its reverse is never spontaneous. And remember, once again, when we start talking about rate, we're no longer speaking of spontaneity; therefore, none of the responses that mention rate are correct either. Therefore, we've got two options left, (a) and (e). From the question above, we should be able to rule out (e) since the reaction is actually ...

Solution Summary

The solutions respond to many multiple choice questions relating to maximum concentration, spontaneous reactions, thermodynamic reactions, reversible processes, etc.

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