Question

Be sure to answer all parts. ΔG o for the reaction H2(g) + I2(g) ⇌ 2HI(g) is 2.60 kJ/mol at 25°C. Calculate ΔG, and predict the direction in which the reaction is spontaneous. The initial pressures are: PH2 = 3.10 atm PI2 = 1.5 atm PHI = 1.75 atm
ΔG =
a. the reaction is spontaneous in the forward direction
b. the reaction is spontaneous in the reverse direction
c. cannot be determined

Answer 1

Answer:

∆G = 1.567 kJ/mole

The reaction is nonspontaneous., or will be spontaneous in the reverse direction

Explanation:

Step 1: The balanced equation

H2(g) + I2(g) ⇌ 2HI(g)        2.60 kJ/mol at 25°C.

Step 2: Data given

The initial pressures are:

pH2 = 3.10 atm

pI2 = 1.5 atm

pHI = 1.75 atm

Step 3: Calculate Q

Kp = (pHI)^2 / (pH2)(pI2)

Q has the same form but we substitute the non-equilibrium values given in the problem.

Q = (1.75)² / (3.10*1.5) = 0.659

Step 4: Calculate gibbs free energy

∆G = ∆G˚ + RTlnQ = 2600 J/mole + (8.31 J/mole K)(298 K)(ln 0.659) = 2600 J/mole - 1032.729 J/mole

= 1567.271‬ J/mole = 1.567 kJ/mole

Interpret ∆G:

∆G > 0 the reaction is nonspontaneous., or will be spontaneous in the reverse direction

∆G < 0 the reaction is spontaneous.

If ∆G  = 0 the reaction is essentially at equilibrium.

∆G = 1.567 kJ/mole

The reaction is nonspontaneous., or will be spontaneous in the reverse direction