Question from text:
"The reaction between phosphorus and chlorine is described by the equation, P4(s) + 6 Cl2(g) ↔ 4 PCl3(l). At equilibrium, the concentration of Cl2 is found to be 0.87 M. Calculate Keq."
Keq = [PCl3]^4 / [P4] [Cl2]^6
I am not seeing how to solve this when I don't have a value for Keq or more than 1 equilibrium value. I know there should be a way to calculate the other values through stoichiometric means, but I cannot seem to find the way!
I tried a straight molar ratio (out of frustration) and found:
0.87mol(Cl2)*1/6=0.145mol(P4)
0.87mol(Cl2)*4/6=.58mol(PCl3)
plugging that into the Keq eqiation:
Keq=[.58]^4/[0.145][0.87]^6
Keq=0.11316496/0.0628757991
Keq=1.7998
(Not the correct answer!)
I THINK your problem is that the value of 0.87 is two significant figures (s.f.) but your answer is 5 s.f. and that isn't kosher. Try rounding your answer to 2 s.f. (1.8) and see if that works.
I am having the same issue. I am wondering if the problem is set up wrong. I tried using ice table to figure it out, but still no luck
Actually it is neither of those responses. There is an exception to the equilibrium rule that is applied here. Solids and liquids are not involved in equilibrium problems. ONLY GASES. Since P4 and PCl3 are solids and liquids they are not considered in the Keq equation. You will only have Keq=1/[Cl2]^6. Plug in the values for 0.87 mol/L to solve your equation. So Keq=1/[.87]^6=1/0.434=2.304 That is your solution.
To calculate Keq, it is necessary to determine the equilibrium concentrations of all the species involved in the equation. In this case, you are given the concentration of Cl2 at equilibrium, which is 0.87 M. However, you need to determine the concentrations of P4 and PCl3.
To solve this, you can use stoichiometry to relate the concentrations of the species. From the balanced equation, you know that the stoichiometric ratio between P4 and Cl2 is 1:6 and between PCl3 and Cl2 is 4:6.
Using this information, you can now calculate the equilibrium concentrations:
1) Start with the given concentration of Cl2: [Cl2] = 0.87 M
2) Use the stoichiometric ratio to determine the concentration of P4:
[P4] = (1/6) * [Cl2] = (1/6) * 0.87 M = 0.145 M
3) Use the stoichiometric ratio to determine the concentration of PCl3:
[PCl3] = (4/6) * [Cl2] = (4/6) * 0.87 M = 0.58 M
Now that you have the equilibrium concentrations of all the species, you can plug them into the Keq expression:
Keq = [PCl3]^4 / [P4][Cl2]^6
= (0.58^4) / (0.145 * 0.87^6)
= 1.7998
So the correct answer for Keq is indeed 1.7998.