# ap chemisrty

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Kp for the following reaction is 0.16 at 25°C.
2 NOBr(g) 2 NO(g) + Br2(g)
The enthalpy change for the reaction at standard conditions is +16.3 kJ. Predict the effect of the following changes on the position of the equilibrium; that is, state which way the equilibrium will shift (left, right, or no change) when each of the following changes is made.
(a) removing some NOBr(g)
(c) decreasing the container volume
(d) decreasing the temperature

• ap chemisrty - ,

Here is what you need to know.
This is a Le Chatelier's Principle problem. Le Chatelier's principle is an elegant one with many elegant words to describe. Students sometimes get lost in the elegant words. Here it is in simple words. Whatever we do to a system in equilibrium, the reaction will shift to UNDO what we did. Simple!.
A. removing NOBr means the reaction will shift to add more NOBr. [Remember: there are only three things to consider. a. the reaction shifts to the right, b. the reaction shifts to the left, c. there is no change.
So let's look at removing NOBr. If it goes to the right, we use up NOBr which makes it smaller. Wrong answer. The reaction shifts to the left. That forms NOBr making it greater. Does that undo what we did. Yes. So that must be the answer.
b. Adding more NOBr. The reaction will shift so as to UNDO what we did meaning it will shift to make NOBr smaller. Which way uses NOBr. That is the shift to the right (see reasoning form part a).
Now you're on your own for c and d but here are some hints.
c. Decreasing volume means increasing pressure. Shift is to side with smaller number of moles.
d. When T is involved, rewrite the equation this way using the information in the problem.
2NO2 + heat ==> 2NO + Br2

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drg