Consider the reaction
HCHO(g) *) H2(g) + CO(g).
1.0 mol of HCHO, 1.0 mol of H2 and 1.0 mol
of CO exist in equilibrium in a 2.0 L reaction
vessel at 600�C.
a) Determine the value of the equilibrium
constant Kc for this system.
2.0 moles of HCHO and 1.0 mol of CO are
then added to this system.
b)Which of the following statements about
this reaction is now true?
1. The forward rate of this reaction is the same as the reverse rate at these new concentrations.
2.The reaction mixture is not at equilibrium, but no further reaction will occur.
3. The reaction mixture remains at equilibrium.
4. The reaction mixture is not at equilibrium, but will move toward equilibrium by using up more HCHO.
5. The reaction mixture is not at equilibrium, but will move toward equilibrium by forming more HCHO.
(HCHO) = (H2) = (CO) = 1 mol/2L = 0.5 M
add (HCHO) = 2/2 = 1.0M
add (CO) = 1/2 = 0.5M
..........HCHO(g) --> H2(g) + CO(g)
E........0.5M........0.5M.....0.5M
add.......1.0M..........0......0.5M
Substitute the E line into Kc expression and calculate Kc.
#2.
a. Since the system is not at equilibrium #1 isn't true.
b. Right, the rxn mixture is not at equilibrium BUT further reaction WILL occur.
c. No, the rxn mixture will MOVE to equilibrium
d & e.One of these is true and the other false. Which way will the reaction shift to reattain equilibrium? Solve for the reaction quotient and compare it with Kc you obtained from #1.
a) To determine the value of the equilibrium constant Kc, we need the balanced equation for the reaction and the concentrations of the species at equilibrium.
The balanced equation for the reaction is:
HCHO(g) ⟶ H2(g) + CO(g)
The concentrations at equilibrium are given as:
[HCHO] = 1.0 mol/2.0 L = 0.5 M
[H2] = 1.0 mol/2.0 L = 0.5 M
[CO] = 1.0 mol/2.0 L = 0.5 M
Now, we can write the expression for the equilibrium constant Kc:
Kc = [H2][CO] / [HCHO]
Substituting the concentration values:
Kc = (0.5)(0.5) / 0.5
Kc = 0.25
Therefore, the value of the equilibrium constant Kc for this system is 0.25.
b) To determine which of the given statements is true when 2.0 moles of HCHO and 1.0 mol of CO are added to the system, we need to analyze the effect of the change in concentrations on the equilibrium.
Statement 3 is correct: The reaction mixture remains at equilibrium.
Explanation: Adding more reactants to the system will shift the equilibrium to the right to consume the additional reactants and reach a new equilibrium. However, the concentrations of all three species are doubled, but their ratios remain the same (1:1:1). As a result, the equilibrium position does not change, and the reaction mixture remains at equilibrium.
Therefore, the correct statement is:
3. The reaction mixture remains at equilibrium.