## 5I.29

Amy Luu 2G
Posts: 105
Joined: Wed Sep 18, 2019 12:19 am

### 5I.29

At 25 C, K 5 3.2 x 10^-34 for the reaction 2HCl(g) $\rightleftharpoons$ H2(g) + Cl2(g). If a reaction vessel of volume 1.0 L is filled with
HCl at 0.22 bar, what are the equilibrium partial pressures of HCl, H2, and Cl2?

In the answer key, they said to assume that x << 0.22. Why do they do this?

Brooke Yasuda 2J
Posts: 102
Joined: Sat Jul 20, 2019 12:17 am

### Re: 5I.29

X must be smaller than .22 because the initial concentration of HCL is .22 M. If the x is larger than .22, then the final equilibrium concentration of HCl would be negative and negative concentrations are not possible.

Daniel Honeychurch1C
Posts: 109
Joined: Thu Jul 11, 2019 12:15 am

### Re: 5I.29

Since K is so small (3.2 x 10^-34), there is very little of the products at equilibrium. Therefore, we know that x is going to be very low. Using this assumption, we can simplify the expression 3.2 x 10^-34 = (x^2) / (0.22 -2x)^2 to 3.2 x 10^-34 = x^2 / (0.22)^2, since x is so small that it will have no effect on this calculation.

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