Homework Help: Chemistry

Posted by K on Saturday, May 28, 2011 at 2:34pm.

Given the equation
NO(g) + 1/2)O^2(g) <-> NO(g) at 457 Kelvin
with a K = 7.5 x 10^2

Find the K value for the equation
2NO^2(g) <-> 2NO(g) + O(g)

Chemistry - DrBob222, Saturday, May 28, 2011 at 4:56pm
I think you have some typos in your post but in general this is what you want.
Easy to remember stuff.
If eqn is doubled, K' is K^2.
If eqn is halved, K' is square root K.
If eqn is tripled, K' is K^3
etc.
If eqn is reversed, K' = 1/K.

If you want to show subscripts on Jishka, it CAN be done but is a lot of trouble. Most of us write
NO₂ as NO2 and all understand the 2 is a subscript. If we want to show a squared term we write NO^2 for NO². The French write NO² for the English of NO₂
Chemistry - K, Saturday, May 28, 2011 at 5:22pm
Hi. Thanks for your help. So this is how I solved the equation.

2NO2(g) <-> 2NO(g) + O2(g)

Since the 2NO2 is reversed from the 1st equation, I got (1/7.5x10^2) and then since the 2NO(g) and the O2(g) are doubled from the 1st equation I got (7.5x10^2)^2 for 2NO(g) and the same for O2(g)

So in the end I get
(1/7.5x10^2)(7.5x10^2)^2(7.5-10^2)2 and my final answer is 4.22 x 10^12

Is that correct?
Chemistry - DrBob222, Saturday, May 28, 2011 at 5:45pm
No. I think you have misunderstood my response.
K = 7.2E2
So for the reversal, you are correct, in 1/7.5E2. The remainder is what you didn't understand properly. You are correct that the equation is doubled BUT you square K, (you squared it twice, once for NO2 and once for O2 and multiplied again by the original K which effectively is K^3. Remember K is the whole term and that's what you are squaring, taking reciprocal, etc and not the individual parts of K.
So what you want to do is for reversing you get 1/7.5E2 and for doubling you get
the squared so the final is 1/(7.5E2)^2 or 1.7777E-6 which rounds to 1.8E-6 rounded to 2 s.f.
Chemistry - K, Saturday, May 28, 2011 at 7:50pm
Thanks so much for your help.

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