3/17/2016
At equilibrium, are the concentrations of NO2 and N2O4
equal?
A. Yes, concentrations have stopped changing.
B. No, concentrations are different when the two concentration lines
are horizontal and flat.
C. Yes, the forward and reverse rates at equilibrium are the same and
thus the two concentrations are equal.
D. No, the forward and reverse rates at equilibrium are not equal and
thus the two concentrations are not equal.
Exercise
• NOCl decomposes slightly at temperatures around 35oC to
form nitric oxide (NO) and chlorine. Kp is 1.6 x 10-5.
• If 1 mol of NOCl is placed in a 2.0 litre flask calculate:
– (i) the final composition, and
– (ii) the final pressure (use the Ideal Gas Law)
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3/17/2016
What happens to the equilibrium 2 SO2 (g) + O2 (g) ⇄ 2 SO3 (g) if the
volume of the system is increased?
A.
B.
C.
D.
The equilibrium shifts to the left
The equilibrium does not change.
The equilibrium shifts to the right.
Cannot determine what happens without knowing the magnitude of
increase in volume
CO2 + H2 ⇄ CO + H2O
If all species are gases and H2O is added, the equilibrium concentration
of CO
a.
b.
c.
d.
will increase.
will decrease.
will remain unchanged.
will disappear.
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3/17/2016
CO2 + H2 ⇄ CO + H2O
Increasing the temperature of this endothermic reaction will _______
[CO] at equilibrium.
a.
b.
c.
d.
increase
decrease
not change
eradicate
CO2 + H2  CO + H2O
Adding a catalyst to this reaction will cause the [CO] at equilibrium to
a.
b.
c.
d.
increase.
decrease.
remain unchanged.
cease to exist.
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3/17/2016
At equilibrium, the rate of the forward reaction is _______ the rate of
the reverse reaction.
a.
b.
c.
d.
equal to
slower than
faster than
the reverse of
The equilibrium constant for the endothermic
decomposition of colorless dinitrogen tetroxide to
form brown nitrogen dioxide
N2O4 (g) ⇌ 2NO2 (g)
1. favors reactants at all temperatures.
2. favors products at all temperatures.
3. favors reactants high temperatures only
4. favors products at high temperatures only.
5. It is impossible to choose between the above
responses without thermochemical data.
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3/17/2016
• Calculate Kp for the reaction of nitrogen and hydrogen to produce
ammonia at 298K. DGfo for ammonia is -16.5 kJ/mol
• What is the industrial relevance of your answer?
• One mole of H2O is heated to 2300K in a 1litre container in an attempt to
decompose it into the elements. The Gibbs energy of reaction at that
temperature, DG, is +118.01 kJ/mol
• Is decomposition favourable or unfavourable at 2300K?
• Will the reaction become more favourable or less favourable as the
temperature increases? Why?
• Calculate K
• Calculate the equilibrium composition of the mixture at 2300K
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3/17/2016
• K varies with temperature. This variation is expressed by the van’t Hoff
equation, which can be written ln(K2/K1) = -DH/R (1/T2 – 1/T1)
• Suppose that you have determined the value of K at several different
temperatures; what should you plot to get a straight line?
• How could you get DH from the plot?
• What sign would you expect DH to have for the decomposition of silver
carbonate? Why?
• For the reaction of sulfur dioxide with oxygen to produce sulfur trioxide
K is 4 x 1024 at 300K and 3 x 104 at 700 K.
• Why does K decrease as T increases?
• Write the balanced equation for the reaction
• Determine the sign of DH
• Comment on your answer
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