
(a)
Interpretation:
Equilibrium reaction of HI with H2 and I2 is given, for the given conditions whether the system is at equilibrium or not has to be checked.
Concept Introduction:
Equilibrium constant(Kc):
Equilibrium constant (Kc) is the ratio of the rate constants of the forward and reverse reactions at a given temperature. In other words it is the ratio of the concentrations of the products to concentrations of the reactants. Each concentration term is raised to a power, which is same as the coefficients in the
Consider the reaction where A reacts to give B.
aA⇌bB
Rate of forward reaction = Rate of reverse reactionkf[A]a =kr[B]b
On rearranging,
[B]b [A]a=kfkr=Kc
Where,
kf is the rate constant of the forward reaction.
kr is the rate constant of the reverse reaction.
Kc is the equilibrium constant.
(a)

Explanation of Solution
Given information,
H2(g) + I2(g) ⇌ 2 HI(g) KC = 50.0 at 745 KH2 = 0.025 mol ; I2 = 0.025 mol and HI = 0.75 molVolume of flask = 20.0 L
Calculate the value of QC,
Conc. of HI = 0.75 mol20.0 L = 0.0375 M ;Conc. of H2 = Conc. of I2 = 0.025 mol20.0 L = 0.00125 M QC = (Conc HI)2(Conc H2) (Conc I2) = (0.0375)2(0.0025) (0.0025) = 900
Compare the value of QC and KC,
QC ≠ KC
Therefore, the given reaction is not at equilibrium for the given conditions.
(b)
Interpretation:
Equilibrium reaction of HI with H2 and I2 is given, for the given conditions the direction of the reaction has to be given.
Concept Introduction:
Refer part (a)
(b)

Explanation of Solution
Given information,
H2(g) + I2(g) ⇌ 2 HI(g) KC = 50.0 at 745 KH2 = 0.025 mol ; I2 = 0.025 mol and HI = 0.75 molVolume of flask = 20.0 L
Calculate the value of QC,
Conc. of HI = 0.75 mol20.0 L = 0.0375 M ;Conc. of H2 = Conc. of I2 = 0.025 mol20.0 L = 0.00125 M QC = (Conc HI)2(Conc H2) (Conc I2) = (0.0375)2(0.0025) (0.0025) = 900
Compare the value of QC and KC,
QC ≠ KC
The given reaction is not at equilibrium for the given conditions.
And also QC > KC so the given reaction must proceeds toward reactants to reach equilibrium condition.
(c)
Interpretation:
Equilibrium reaction of HI with H2 and I2 is given, concentrations of all three substances has to be calculated.
Concept Introduction:
Refer part (a)
(c)

Explanation of Solution
Given information,
H2(g) + I2(g) ⇌ 2 HI(g) KC = 50.0 at 745 KH2 = 0.025 mol ; I2 = 0.025 mol and HI = 0.75 molVolume of flask = 20.0 L
Construct ICE table,
H2(g) + I2(g) ⇌ 2 HI(g) Initial conc. (M) 0.00125 0.00125 0.0375Change in conc. (M) + x + x - 2 xEquilibrium conc (M) 0.00125 + x 0.00125 + x 0.0375 - 2 x
At equilibrium,
KC = [HI]2[H2] [I2] = (0.0375 - 2x)2(0.00125 + x) (0.00125 + x) = 50.0
Solve for x,
take square root of each side, (0.0375 - 2x)(0.00125 + x) = √50.0 = 7.07 0.0375 - 2x = 0.0088 + 7.07 x 0.0375 - 0.0088 = 9.07xtherefore, x = 0.0032 M
Calculate the concentrations,
[H2] = [I2] = 0.00125 + x = 0.00125 + 0.0032 M = 0.0045 M[HI] = 0.0375 - 2 x = 0.0375 M - 2 (0.0032 M) = 0.0375 M - 0.0064 = 0.031 M
Therefore, the concentration of H2 and I2 is 0.0045 M and the concentration of HI is 0.031 M.
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