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$\ce{Heat\ +\ PCl5(g)\ \rightleftharpoons\ PCl3(g)\ +\ Cl2(g)}$

According to the process above, which of the following can be done to increase the number of moles of $\ce{Cl2}$ in a sealed container at equilibrium?

  1. Reducing temp
  2. Increasing the pressure at a constant temp
  3. Adding more moles of $\ce{PCl5}$

I'm pretty sure it's not 1. but I'm stuck between 2. and 3. Are they both true or only one of them?

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Hint:

For 2. Try to apply Le Chatelier's principle. Increasing pressure will make the system try to decrease it and there is one side of the equilibrium with an unequal number of moles.

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  • $\begingroup$ I just looked up the pressure part of Le Chatelier's principle and it said that an increase of pressure would shift the equilibrium toward the side with fewer moles and in this case its the side opposite the CL2. So i'll take it that 2 is not true because the equilibrium is shifting in the opposite direction? $\endgroup$ – sloth1111 Jan 4 '14 at 17:11
  • $\begingroup$ @sloth1111 That's right! :) $\endgroup$ – Jerry Jan 4 '14 at 17:17
  • $\begingroup$ I'm guessing the the answer is III because it's not I, if you increase the pressure, the equilibium will shift toward the PCL5 because there's less moles on that side, and III is true because adding more PCL will shift equilibrium to the other side, increasing CL2. Am I correct? $\endgroup$ – sloth1111 Jan 4 '14 at 17:23
  • $\begingroup$ @sloth1111 Yup, you are correct and you're welcome :) $\endgroup$ – Jerry Jan 4 '14 at 17:27
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yest the answer 3. is correct. It will be even more effective to adding more $\ce{PCl5}$ and increasing temperature too.

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  • $\begingroup$ Ok thank you!! I assumed it would be 3 because of what you said above. Adding PCL5 would have the greatest impact. $\endgroup$ – sloth1111 Jan 5 '14 at 17:31

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