Question

Using this data,
2 NO(g) + Cl2(g) == 2 NOCl(g) Kc = 3.20 X 10-3
NO2(g) == NO(g) + ½ O2(g) Kc = 3.93
calculate a value for Kc for the reaction,


NOCl (g) + ½ O2 (g) == NO2 (g) + ½ Cl2 (g)


A. 20.2
B. 2.06 X 10-4
C. 4.49
D. 4.84 X 10-3
E. 0.223

eliminated down to b or d
but going with b unless wrong



chemistry - DrBob222, Monday, March 12, 2012 at 6:46pm
I disagree with b AND d.
Use equation 1, take 1/2 of it, and reverse it. K1 for that will be 1/sqrt Kc.
Multiply k1 by equation 2 reversed so k2 = 1/Kc
Then k1*k2 = ?
Check my manipulations to be sure you get the equation in the problem.



chemistry - bob, Monday, March 12, 2012 at 9:03pm
when you reverse it do you get a negative?

-3.20x10-3/2=-1.6x10-3
1/.04=25
1/3.93=.254
25x.245
=6.125
not an answer choice?

Answer 1

No negatives are involved. When reversing Keq, it is k' = 1/Keq.
My instruction was that k1 = 1/sqrt Kc. You took 1/2 of it; that's to get the coefficients right when you add one equation to the other but k1 = 1/sqrt Kc. [When taking 1/2 of an equation, k1 is sqrt Kc. Then take the reciprocal when reversing it.
That's (1/sqrt 0.0032) and I get something like 18 or so. The 1/3.93 part looks ok.

Answer 2

That's my answer, too.