Chem 11600 Part 3

Category 1

100

When is ΔG spontaneous? When it is greater or less than 0?

less than 0

200

H₂O(g)→H₂O(s)

What are the signs of ΔH and ΔS for this process?  Explain

Is the process spontaneous at all T, no T, low T, or high T?  Explain

ΔS < 0 and ΔH < 0

Since ΔS is negative, the –TΔS term is positive. In order for ΔG to be < 0, the temperature must be low.

300

At 298 K, 

ΔG = –141.6 kJ;

ΔH = –198.4 kJ  

ΔS = –187.9 J/K

ΔG < 0 at 209 K (= 25.0^o C), so the reaction is spontaneous.

ΔG will become less negative, and the reaction less spontaneous, with increasing T

400

2SO₂(g) + O₂(g) → 2SO₃(g)

Calculate K at 298 K and at 973 K, (ΔGº298 = −141.6 kJ/mol of reaction as written; using ΔHº and ΔSº values at 973 K,

  ΔGº973 = −12.12 kJ/mol for reaction as written.)

ΔGº = −RT lnK   so K = e^{−(ΔG°/RT)}

K at 298 K = e^57.2 = 7x10²⁴

500

balance

MnO₄^–(aq) + C₂O₄^2–(aq) → MnO₂(s) + CO₃^2–(aq)  [basic solution]

2MnO₄^–(aq) + 3C₂O₄^2–(aq) + 4OH–(aq) → 2MnO₂(s) + 6CO₃^2–(aq) + 2H₂O(l)

Category 2

100

When does the sign of ΔG switch from (-) to (+)?

T=ΔH/ΔS

200

When Q < K, ΔG is greater or less than 0

less than

300

According to the equation, ΔG^o  = –RT lnK, when ΔG^o becomes more positive, K becomes smaller or larger?

smaller

400

Which electrode produces electrons?

Anode

Category 3

100

Define oxidation

The loss of electrons.

The reducing agent loses electrons and is oxidized

200

Determine the oxidation number (O.N.) of each element in these balanced reactions:

2Al(s)  +  3H₂SO4(aq) →  Al₂(SO4)₃(aq) +  3H₂(g)

2Al=0

3H₂SO4(aq)=+6

Al₂(SO4)₃(aq)=+6

3H₂(g)=0

300

Is a voltaic cell spontaneous or is a electrolytic cell spontaneous?

Voltaic cell (ΔG < 0)

Category 4

100

Define combustion reaction

–the process of combining with O₂

Category 5

100

Where does oxidation occur in electrochemical cell?

Anode