## Calculating Equilibrium constant

$\Delta G^{\circ}= \Delta H^{\circ} - T \Delta S^{\circ}$

$\Delta G^{\circ}= -RT\ln K$

$\Delta G^{\circ}= \sum \Delta G_{f}^{\circ}(products) - \sum \Delta G_{f}^{\circ}(reactants)$

Kira_Maszewski_1B
Posts: 17
Joined: Wed Sep 21, 2016 2:57 pm

### Calculating Equilibrium constant

The standard reaction free energy for H2(g)+I2(g) <-->2HI(g) is DeltaG = -21.1 kj at 500K. In a sealed reaction container, the equilibrium partial pressures of the gases are PH2= 1.2 bar, PI2 = 1.5 bar, and PHI is unknown.

a) Calculate the value of the equilibrium constant for this reaction.
b) Calculate the equilibrium partial pressure pressure of HI(g).

Cherry_Deng_1K
Posts: 12
Joined: Wed Sep 21, 2016 2:55 pm

### Re: Calculating Equilibrium constant

Hello,

For part (a), I would start by using the equation ΔG°= -RT ln K. Since the standard reaction free energy is already given, you can just directly substitute ΔG°, R, and T to find the equilibrium constant, K. Since ΔG° is given in kJ and the unit for R is J/(K mol), don't forget to convert kJ to J to make sure the calculations are consistent! For part (b), since you have just calculated the equilibrium constant K and you are given the equilibrium partial pressures for H2 and I2, you can directly substitute it into the general equation K = P(HI)^2 / [P(I2) x P(H2)] (you learned this in Chem 14A). If you do your calculations correctly, you should be able to find the partial pressure of HI. Hope this helps!