[aning]

Equal masses (.500 g each) of H₂ and O₂ are placed in an evacuated 4.00 L flask at 25.0 C. The mixture is allowed to react to completion and the flask is retunred to 25.0 C and allowed to come to equilibrium. The equilibrium vapor pressure of water at 25.0 C is 23.76 torr.

a. Write and balance an equation for the reaction.
2 H₂ + O₂  <==>  2 H₂O

b. What is the total pressure inside the flask before the reaction begins?
.5g H₂ / 2.02g H₂ = .248 mol H₂
.5g O₂ / 32g O₂ = .0156 mol O₂
PV = nRT
P = (.2636mol * 62.4 * 298K) / 4L = 1230 torr

c. What is the mass of water vapor in the flask at equilibrium?
PV = nRT
I used the equilibrium vapor pressure of water as P, but I'm not sure if this is correct
(23.76 torr)(4L) = n(62.4)(298K)
n = .00511 mol H₂O
.00511 mol H₂O*18.02g = .0921g of water

d. How many gras of which reactant gas remains at equilibrium?
I did a limiting reactant problem, and I found that H₂ is left over.
Since .00511 mol of H₂ is used in the equilibrium process, so .243 mol remains at equilibrium? [I'm not sure about this answer at all]

e. What is the total pressure inside the flask at equilibrium?

f. After the reaction, is there any liquid water present? If so, how many grams? If not, why not?

[Borek]

Equal masses (.500 g each) of H₂ and O₂ are placed in an evacuated 4.00 L flask at 25.0 C. The mixture is allowed to react to completion and the flask is retunred to 25.0 C and allowed to come to equilibrium. The equilibrium vapor pressure of water at 25.0 C is 23.76 torr.

a. Write and balance an equation for the reaction.
2 H₂ + O₂  <==>  2 H₂O

b. What is the total pressure inside the flask before the reaction begins?
.5g H₂ / 2.02g H₂ = .248 mol H₂
.5g O₂ / 32g O₂ = .0156 mol O₂
PV = nRT
P = (.2636mol * 62.4 * 298K) / 4L = 1230 torr

c. What is the mass of water vapor in the flask at equilibrium?
PV = nRT
I used the equilibrium vapor pressure of water as P, but I'm not sure if this is correct
(23.76 torr)(4L) = n(62.4)(298K)
n = .00511 mol H₂O
.00511 mol H₂O*18.02g = .0921g of water

So far so good, but you should check - just in case - if that's not more than the amount of water produced.

d. How many gras of which reactant gas remains at equilibrium?
I did a limiting reactant problem, and I found that H₂ is left over.
Since .00511 mol of H₂ is used in the equilibrium process, so .243 mol remains at equilibrium? [I'm not sure about this answer at all]

You are right about limiting reagent approach, but 0.00511 is not the amount used.

In general you may assume reaction went to completion, producing as much water as limiting reagent allowed. The only equilibrium that you have to deal with is the one between liquid water and its vapor.