Gen Chem Question - Confusion

[creative8401]

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Hi everyone. Hope you are all doing great. I have a chem question that seems confusing, and it uses Le Chatlier's Principle.

The photodissociation of hydrogen peroxide gas may be induced simply by exposing the reactant to light. The products of this reaction and H2O (l) and O2 (g). All of the following would make the photodiss. reaction shift to the right except:

light + H2O2 (l) --> H2O (l) + 1/2 O2(g)

A: an increase in heat
B: a drecase in O2 pressure
C: an increase in amount of H2O2

I understand how these will all shift to right, but

D: a decrease in pressure
E: an increase in pressure

Answer is D, but I do not understand why. There is 1 mole on the left, 1 and half on the right, if we decrease the pressure, wouldn't it shift to the right? Shouldn't the answer be an increase in pressure E?

Thank you.

 

[DentalDeac]

Is the H2O2 gas or liquid? You wrote that it was gas but then said H2O2 (l)

 

[creative8401]

My bad, its hydrogen peroxide gas: H2O2 (g)

thank you

 

[Mstoothlady2012]

!

 

[DentalDeac]

Ok. So you have 1 mol of gas on the left, and 1/2 a mol of gas on the right.

Whenever you increase the pressure, the reaction will be favored on the side of the reaction with less moles of gas (the right). Conversely, when you decrease the pressure, the reaction will be favored on the side of the reaction with more moles of gas - the left.

The answer is D. Does that make sense?

 

[DentalDeac]

The reaction is balanced, so you have 1 mol on the left and 1 & 1/2 mol on the right. So when you decrease the pressure the reaction will shift towards the less mol side. Hence, it will shift to the left.

This is wrong. When we are talking about pressure, we are only concerned with moles of gas, so its 1 mol on the right, 1/2 mol on the left. Increasing pressure will favor the right, decreasing pressure will favor the left.

 

[bergoshe]

Ok. So you have 1 mol of gas on the left, and 1/2 a mol of gas on the right.

Whenever you increase the pressure, the reaction will be favored on the side of the reaction with less moles of gas (the right). Conversely, when you decrease the pressure, the reaction will be favored on the side of the reaction with more moles of gas - the left.

The answer is D. Does that make sense?

This is spot on, was just about to type it myself!

 

[Mstoothlady2012]

Ok. So you have 1 mol of gas on the left, and 1/2 a mol of gas on the right.

Whenever you increase the pressure, the reaction will be favored on the side of the reaction with less moles of gas (the right). Conversely, when you decrease the pressure, the reaction will be favored on the side of the reaction with more moles of gas - the left.

The answer is D. Does that make sense?

exactly...that is what i was trying to say...got a little confuse typing lol

 

[Mstoothlady2012]

This is wrong. When we are talking about pressure, we are only concerned with moles of gas, so its 1 mol on the right, 1/2 mol on the left. Increasing pressure will favor the right, decreasing pressure will favor the left.

I am sure you meant to say 1 mol on the left and 1/2 mol on the right. Increasing pressure will shift to the right and decreasing pressure will shift to the left

 

[DentalDeac]

I am sure you meant to say 1 mol on the left and 1/2 mol on the right. Increasing pressure will shift to the right and decreasing pressure will shift to the left

Right right, thanks for correcting me haha.

 

[doc toothache]

My bad, its hydrogen peroxide gas: H2O2 (g)

thank you

Since H2O2 has a boiling point of 150.2 C how are you going to have H2O (l) on the right side of the equation?
The reaction takes place as written (H2O2 as l) at rt, and that is why peroxide is usually stored in amber containers.

A decrease in (atm) pressure allows the oxygen to bubble out of solution, whereas an increase in P will have the opposite effect.

 

[osimsDDS]

So when were talking about pressure and the relative moles we ONLY count the gaseous moles in the balanced equation??? I thought it was all states solid, liquid, gas...

 

[Mstoothlady2012]

So when were talking about pressure and the relative moles we ONLY count the gaseous moles in the balanced equation??? I thought it was all states solid, liquid, gas...

nope just gases