A 0.100 mol sample of H2S is placed in a 10.0 L reaction vessel and heated to 1132°C. At equilibrium, 0.0285 mol H2 is present. What is the value of Kc at this temp?


2 H2S(g) 2 H2(g) + S2(g

After I do my calculations, I get

Kc= (0.0057)2 X (0.00285)/(0.0043)2

and get 5.03 X 10-3

the book says the answer is 2.3 X 10-4

What am I doing wrong?

Kc=5.01x10^-3,your answer is correct i dont know which book were you using

To find the value of Kc, you need to use the equilibrium concentrations of the species involved in the reaction. In this case, the equilibrium concentrations are 0.0285 mol for H2 and 0.0043 mol for H2S (since 0.100 mol - 0.0285 mol = 0.0715 mol).

The balanced equation for the reaction is: 2 H2S(g) ↔ 2 H2(g) + S2(g)

The expression for the equilibrium constant, Kc, is given by:
Kc = ( [H2]² × [S2] ) / ( [H2S]² )

Plugging in the given values:
Kc = ( (0.0285 mol/L)² × 0.0043 mol/L ) / ( (0.0043 mol/L)² )

Simplifying the equation:
Kc = (0.00081225) / (0.00001849)
Kc ≈ 43.92

Therefore, the correct value for Kc at this temperature is 43.92, not 2.3 × 10^(-4). It appears there may have been a mistake in the book.

To determine the value of Kc at this temperature, you can use the equilibrium concentrations of the reactants and products.

Given:
- Initial moles of H2S = 0.100 mol
- Equilibrium moles of H2 = 0.0285 mol
- Volume of reaction vessel = 10.0 L

First, you need to calculate the equilibrium concentrations of the reactants and products. To do this, divide the moles present at equilibrium by the volume of the reaction vessel.

Equilibrium concentration of H2S: [H2S] = 0.100 mol / 10.0 L = 0.0100 M
Equilibrium concentration of H2: [H2] = 0.0285 mol / 10.0 L = 0.00285 M

Next, substitute these concentrations into the expression for Kc:

Kc = ([H2]^2[S2]) / ([H2S]^2)

Kc = (0.00285^2) / (0.0100^2)

Kc = 8.1225 / 0.0100

Kc = 812.25

Therefore, the value of Kc at this temperature is 812.25, not 5.03 × 10^-3 as calculated by you, or 2.3 × 10^-4 as stated by the book.

It seems that there was an error in your calculation or data entry. Double-check your calculations and make sure that you are using the correct equilibrium concentrations when plugging into the Kc expression.

I don't believe you are doing anything wrong although I obtained 5.01E-3 for Kc.

Everything looks ok to me. Just to make sure I started with 0.1mol/10L = 0.01M and set up 2H2S ==> 2H2 + S2
Kc = 5.01E-3 = (H2)^2(S2)/(H2S)^2 and solved the cubic equation. I obtained 0.00285M for x = (S2) so 5.01E-3 must be right.