Textbook 5I

[Kayley Steele 3D]

I am confused on question 5I.13 in the textbook. I know we need to use an ICE box to calculate the equilibrium composition but I keep getting a much different answer than the book. Could someone explain the steps for part a?

In an experiment, 2.0 mmol Cl2(g)was sealed into a reaction vessel of volume 2.0 L and heated to 1000. K to study its dissociation into Cl atoms. Use the information in Table 5G.2 to calculate the equilibrium composition of the mixture.

[Amy Xia 1J]

The equation for the reaction is Cl2(g) --- 2Cl(g)
The initial concentration for Cl2 is 2.0mmol/2.0L = 0.001M
Then set the ice table, Cl2 = 0.001 - x 2Cl = +2x
by using the equilibrium constant 1.2 x 10^-7, we could get x and then get the final concentration of Cl2 by subtracting x from 0.001, and get final concentration of Cl by times 2 of x.

[Likhitha Yettela 1F]

I also was confused. make sure when you are looking at the chart, you look at the KC value and not the K value.

[Jenny Han 3F]

Agreed with Likhitha! To clarify, use Kc instead of K because the problem uses mmol and L and Kc uses concentrations. K would be for partial pressure.