"quick" way to solve changes in pressure

[Kathryn 1F]

In class friday, Lavelle talked about a "quick" way to tell which way the reaction shifts when the volume decreases based on how many moles of gas there will be? Can someone please explain this? Does it have to do with balancing equations?

In class he referred to the example N2 + 3H2 -> 2NH3

[julia_lok_2K]

Based on the balanced reaction, if the volume decreases and there are more moles of gas on the left, the reaction will shift to the right. If there are more moles of gas on the right, the reaction will then shift to the left. This happens because the side with more moles of gas would have a larger pressure, so in order to alleviate that the reaction would shift to the opposite direction. In other words, this complies with Le Chatelier's principle.

Hope this helps!

[105114680]

Concentration is equal to moles/liters. By decreasing the volume by compression (decreasing liters), the concentration of the substances is increased (since the amount of moles are initially constant before the equilibrium adjusts). To adjust, the equilibrium will shift in the direction of the least amount of moles of gas to lower the concentration.

[deepto_mizan1H]

It's a way to estimate how the moles factor in to the pressure of each part of the system, a "quick" way to understand which direction it'll go. But overall it'll help to check logically each step.