## "Quick way" part in Lecture

JustinHorriat_4f
Posts: 111
Joined: Wed Sep 18, 2019 12:19 am

### "Quick way" part in Lecture

What are examples that can differentiate when it says " V decreases and more moles of gas on left" and "V decreases, and more moles of gas on right"? I was very confused when looking over my notes again.

KSong_1J
Posts: 101
Joined: Thu Jul 11, 2019 12:17 am

### Re: "Quick way" part in Lecture

Did you mean to write something like “if volume decreases and there’s more moles of gas on the left, then the reaction shifts to the right” and “if volume decreases and there’s more moles of gas on the right, then the reaction shifts to the left”?

JustinHorriat_4f
Posts: 111
Joined: Wed Sep 18, 2019 12:19 am

### Re: "Quick way" part in Lecture

Yes, what does that mean?

KSong_1J
Posts: 101
Joined: Thu Jul 11, 2019 12:17 am

### Re: "Quick way" part in Lecture

If you decrease the volume in the system, then the reaction will favor the direction that has fewer moles of gas (since, according to Le Chatelier’s principle, when stress is applied to a system in equilibrium, the equilibrium will shift to reduce the effect of the stress). By reducing the volume, you increase the pressure of the system, so if there’s more moles of gas on the left in a reaction, then the reaction will want to shift to the right because that reduces the pressure and vice versa. I hope that helps a little! :)

GFolk_1D
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Joined: Fri Aug 09, 2019 12:15 am

### Re: "Quick way" part in Lecture

I am also a bit confused on this topic. Can someone please explain the difference between the quick way and the actual reasoning to solve these types of problems? Thanks

VLi_2B
Posts: 99
Joined: Sat Sep 14, 2019 12:15 am

### Re: "Quick way" part in Lecture

The quick way is to count the number of moles on each side of the reaction equation and compare which side has the greater number of moles to determine which way the reaction will favor.

N2(g) + 3H2(g) <=> 2NH3(g)
Reactants: 1 mol of N2 + 3 mols of H2
Products: 2 mols of NH3

4 mols of reactant to 2 mols of product

Since there are more moles of reactant, the reaction will shift to favor the products.

Tiffany_Chen 2K
Posts: 106
Joined: Fri Aug 30, 2019 12:15 am

### Re: "Quick way" part in Lecture

Look at PV=nRT but rearranged into P=((n/V)*RT) or P=conc*RT. For example, volume is halfed ->> n will double. You can then recalculated Qc and compare this to Kc to determine which way the reaction will go.

Katie Bart 1I
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Joined: Sat Aug 24, 2019 12:16 am

### Re: "Quick way" part in Lecture

Does the quick way work every time? Or only in certain scenarios?

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