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The equilibrium constant is a constant as long as the temperature remains constant. Changing the temperature of a system at equilibrium will result in a new value of Kc.
Kc at 350K
Kc = [BrCl]^2 / [Br2] [Cl2] = 0.0150 / 0.0550 / 0.0850 = 0.0481
At 380 Kc = 0.0175. This means that Kc has decreased, which means that the equilibrium shifts to the left as T increases. The reaction is exothermic.
At equilibrium the new concentrations will be ...
[BrCl] = 0.0150 - 2x
[Br2] = 0.0550 + x ..... [New equation. - replaced by +, Br2 and Cl2 concentrations will
[Cl2] = 0.0850 + x ......[increase, not decrease. Ooops. Too late at night.
Kc = (0.0150 - 2x)^2 / (0.0550 + x) / (0.0850 + x) = 0.0175
solve for x (I'm going to use my TI-86 with "solver", otherwise you can dust off your algebra skills.)
x = 0.0028 .... [Updated this value]
[BrCl] = 0.0150 - 2x = 0.0094 M
[Br2] = 0.0550 + x = 0.0578M
[Cl2] = 0.0850 + x = 0.0878 M
============ Follow up ==================
Now, they are correct. I had all the concentrations decreasing. Bad idea. When the equilibrium shifts to the lift, the BrCl concentration drops, but the Br2 and Cl2 concentrations increase. All is well with the world, now. Updated answers are given above, and comments are in [brackets].
Kc at 350K
Kc = [BrCl]^2 / [Br2] [Cl2] = 0.0150 / 0.0550 / 0.0850 = 0.0481
At 380 Kc = 0.0175. This means that Kc has decreased, which means that the equilibrium shifts to the left as T increases. The reaction is exothermic.
At equilibrium the new concentrations will be ...
[BrCl] = 0.0150 - 2x
[Br2] = 0.0550 + x ..... [New equation. - replaced by +, Br2 and Cl2 concentrations will
[Cl2] = 0.0850 + x ......[increase, not decrease. Ooops. Too late at night.
Kc = (0.0150 - 2x)^2 / (0.0550 + x) / (0.0850 + x) = 0.0175
solve for x (I'm going to use my TI-86 with "solver", otherwise you can dust off your algebra skills.)
x = 0.0028 .... [Updated this value]
[BrCl] = 0.0150 - 2x = 0.0094 M
[Br2] = 0.0550 + x = 0.0578M
[Cl2] = 0.0850 + x = 0.0878 M
============ Follow up ==================
Now, they are correct. I had all the concentrations decreasing. Bad idea. When the equilibrium shifts to the lift, the BrCl concentration drops, but the Br2 and Cl2 concentrations increase. All is well with the world, now. Updated answers are given above, and comments are in [brackets].