Introduction to Equilibrium - the 10 Questions



1 The appropriate expression for the equilibrium constant Kp for the gas phase reaction between nitrogen and hydrogen to form ammonia is:
(PH2)3(PN2)/(PNH3)2
PNH3/(PH2)(PN2)
(PNH3)2/(PH2)3(PN2)
(PH2)(PN2)/PNH3
2 Consider the reverse of the reaction in question 1, the decomposition of ammonia into the elements. Which of the following is the correct expression for the equilibrium constant of this new reaction, call it K2, and the equilibrium constant for the first reaction, call that one K1?
There is no relationship between the two since they refer to different reactions.
K2 = K1
K2 = -K1
K2 = 1/K1
3 How do the mathematical expressions for, and the values of, the equilibrium constant K, and the reaction quotient Q, compare for any reaction.
Both the mathematical forms and the values are different.
Both the mathematical forms and the values are different.
The mathematical forms are the same, the values are the same only when the system is at equilibrium.
The forms differ, but the values are the same.
4 The concentration equilibrium constant (Kc) for the reaction
H2 + I2 --> 2 HI has a value of 60 at 350oC. For the three sets of conditions given here, decide if the reaction is at equilibrium, will form additional product as equilibrium is reached, or will form additional reactant as equilibrium is reached:
(a) [H2] = [I2] = [HI] = 0.010M
(b) [H2] = 0.010M; [I2] = 0.15M; [HI] = 0.30M
(c) [H2] = [HI] = 0.10M; [I2] = 0.0010M
(a) will produce more HI (product); (b) is already at equilibrium and (c) will produce more reactant
all three will produce more product
all three will produce more reactant
(a) and (c) will produce more product; (b) is already at equilibrium
5 What fundamental precept of chemical equilibrium is best illustrated by the figure below?
equil1.gif
The rate of the reaction slows down as equilibrium is approached.
The reaction of H2 with I2 is exothermic.
The concentrations of reactants are products present at equilibrium are the same whether we start with only the reactants (right hand graph) or only the products (left hand graph).
Chemical equilibrium is dynamic in nature.
6 Suppose you have a system containing H2, I2 and HI that is at equilibrium at a given temperature. You are monitoring the concentration of I2 by absorption (what color is I2; in what region of the visible spectrum would you expect it to absorb light). On heating the system, you find that the absorption increases. Which of the following is the most reasonable inference that you can draw from this observation? (Assume that you are measuring the absorption at a wavelength where H2 and HI do not absorb.)
The reaction H2 + I2 --> 2 HI is endothermic.
The reaction H2 + I2 --> 2 HI becomes more favored at higher temperatures.
The reverse reaction rate is greater at the higher temperature.
The reaction H2 + I2 --> 2 HI is exothermic.
7 The equilibrium constant for the reaction Cl2 + F2 --> 2 ClF (all gases) is 20 at 2500K. At one particular time you measure the concentrations of these three species to be: [Cl2] = 0.37M; [ F2] = 0.25M and [ClF] = 0.85M. If you measure the concentrations again after a suitable time interval, will you find that the concentration of ClF has increased, decreased, or stayed the same?
Increased
Decreased
Stayed the same because the system is already at equilibrium.
Stayed the same because the reaction is very slow.
8 Express the equilibrium constant for the reaction
2 C(s) + 3 H2(g) --> C2H6(g)
in terms of the equilibrium constants for the reactions:

1. 2 C2H6(g) + 7 O2(g) --> 4 CO2(g) + 6 H2O(l) K1

2. C(s) + O2(g) --> CO2(g) K2

3. 2 H2(g) + O2(g) --> H2O(l) K3
K1K2K3
K22K31.5/K10.5
K2K3/K1
K22K31.5K10.5
9 K for the reaction CCl4(g) --> C(s) + 2 Cl2(g) at 700K is 0.76 atm. What initial pressure of CCl4(g) is needed to produce a total pressure of 1.2 atm at equilibrium?
1.53atm
1.2 atm
0.88 atm
0.64 atm
10 The water-gas shift reaction, C(s) + H2O(g) --> CO(g) + H2(g) is used in the process of coal gasification since both products burn in oxygen. KP for this reaction is 48atm at 1300K. What mass of carbon is gassified at this temperature when 10.0atm of water vapor is introduced into a 100 liter vessel containing coal? Be careful about what you do and do not include in the K expression - water is not a liquid or the solvent here.
102g
16.9g
95.7g
21.3g