Spontaneous Reactions: Chapter 15 Quiz #2

ΔH-

Exothermic Sign

ΔH+

Endothermic Sign

ΔS +

Increase in entropy Sign

ΔS -

Decrease in entropy Sign

Yes always

Is this spontaneous? ΔH- ΔS+

Sometimes. If temperature is high enough

Is this spontaneous?ΔH+ ΔS+

Sometimes. If temperature is low enough

Is this spontaneous?ΔH- ΔS-

Never

Is this spontaneous?ΔH+ ΔS-

ΔH is negative

ΔS is positive

The conditions in which ΔG is always negative is when ΔH is ... and ΔS is ...

Gibbs Free Energy Equation

ΔG = ΔH - TΔS

ΔH is negative

ΔS is positive

The conditions in which ΔG is always negative is when ΔH is ... and ΔS is ...

ΔH is +

ΔS is -

Conditions in which ΔG is always positive is when ΔH is ... and ΔS is ...

Positive

if reactants break up into smaller products/ more of them then entropy is

Positive

if reactant is a solid and product is a liquid entropy is

Spontaneous reaction

a physical or chemical change that occurs with no outside intervention

Entropy

a measure of disorder or randomness of the particles that make up a system

Second Law of thermodynamics (Law of Disorder)

- Spontaneous processes always proceed in such a way that the entropy of the universe increases

- The sum total of entropy must always increase

Free energy

the energy that is available to do work

Gibbs Free Energy Equation

ΔG = ΔH - TΔS

negative

If the reaction is spontaneous, ΔG is

a. G = H - TS

G = 491.18 kJ - (298 K)(0.197.67kJ/K) = + 432.27 kJ

b.No, it is not spontaneous at 25 C (G is a large positive value)

a. Calculate the standard free energy change, ΔG, for the following at 25 degree C:

MgO(s) + C(graphite) --> Mg(s) + CO(g)

ΔH = 491.18 kJ ΔS = 197.67 J/K

b. Is this reaction spontaneous at 25 degree C?

a. exothermic ∆H (-)

b. decrease ∆S (-)

c. sometimes (low temperatures)

CH4 (g) + O2 (g) --> CO2(g) + H2O (l) ΔH = - 890 kJ

a. Is the reaction endothermic or exothermic?

b. Does this reaction increase or decrease in entropy?

c. Is this reaction sometimes, always or never spontaneous?