Equilibrium of NOCL Change w/ Added NO & Cl2

In summary: It is not clear what you are trying to say. We are not told anything about pressure, volume, temperature, or the initial concentrations of NO and NOCl. The only thing we know is that equal moles of NO and NOCl are added to the mixture at constant temperature. So we cannot make any assumptions about the pressure being constant or the concentration of only one substance decreasing. The answer to this question would depend on the specific conditions and equilibrium constant, which are not given.
  • #1
Faiq
348
16

Homework Statement



2NOCl(g) <--> 2NO(g) +Cl2(g)[/B]
What will be the effect on equilibrium concentration of NOCL when equal moles of NOCL and NO are introduced in the mixture at constant temperature?

Homework Equations


Kconcentration = [NO]2[Cl2] / [NOCl]2

The Attempt at a Solution


In my opinion, the concentration of NOCl will decrease because the number of moles of chlorine is less than the new equilibrium concentration and so NOCl will decompose to give more chlorine.
 
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  • #2
What if - before adding NOCl and NO - you leave them in a separate vessel till they reach their own equilibrium, and you combine two equilibrated mixtures?
 
  • #3
But even if in the equilibrium of NOCl and NO, if NOCl is trying to reach equilibrium each attempt would result in much more production of Cl2
 
  • #4
Question doesn't ask about what happens to the concentration of Cl2.

Assuming you combine two mixtures at equilibrium - does the reaction proceed?

In general the question is poorly worded, as it is not entirely clear what it means "introduced into the mixture". Keeping pressure constant? Keeping volume constant? Each case is slightly different and should be treated separately, but in general I have yet to see a case where adding a substance to the mixture results in lowering its amount. Sure, final amount can be lower than the sum of initial+added, but I have never seen a case where final is lower than the initial without added.
 
  • #5
Faiq said:

The Attempt at a Solution


In my opinion, the concentration of NOCl will decrease because the number of moles of chlorine is less than the new equilibrium concentration and so NOCl will decompose to give more chlorine.

If there is something, as was said, misleading about the question, it is that it maybe suggests that there is an answer like this.

Anyway you are not asked about the concentration of just one thing.

I presume the answer would have to be on the lines of "it depends on..." And then the answer is rather generic and almost trivial.
 
  • #6
The temperature has remained constant so the pressure is also constant.
and in my opinion the concentration of NOCl should decrease to compensate for the less moles of Cl2
 
  • #7
Faiq said:
The temperature has remained constant so the pressure is also constant.
and in my opinion the concentration of NOCl should decrease to compensate for the less moles of Cl2

Where does the bolded part come from? I am not sure what it even means.

I don't think there can be a unique answer to this question In the form either increases or decreases. We are not told an equilibrium constant or conditions, pressures or anything. Still if the equilibrium constant was such as to strongly favour NOCl, then introducing equimolar NO and NOCl will result in a net reaction of NO with any chlorine about (about which we are not told either) increasing NOCl.

Then when you say the pressure is constant, if this is a closed vessel (about which again we are not told) then during the reaction it cannot stay constant!

So one of two things: If the question is as you have related it, then in your answer you have to reframe, restate, the question so that it is clear what you are answering. Or else if, as very frequently happens here, a question has not been accurately relayed, then you should give it to us exactly.verbatim.
 
Last edited:
  • #8
Faiq said:
The temperature has remained constant so the pressure is also constant.

Say, you have 1 mole of gas in 22.4 L tank, at 0°C. The pressure is - as it is easy to calculate - 1 atm. Now you add another mole of gas to the same tank, keeping the temperature at 0°C. Temperature has not changed - is the pressure still 1 atm?

Faiq said:
and in my opinion the concentration of NOCl should decrease to compensate for the less moles of Cl2

You were told several times what is wrong with this line of thinking.
 

Related to Equilibrium of NOCL Change w/ Added NO & Cl2

1. What is the equilibrium expression for the reaction between NO and Cl2?

The equilibrium expression for the reaction between NO and Cl2 is Kc = [NOCl]^2 / [NO]^2[Cl2], where [ ] represents the molar concentration.

2. How does the addition of NO and Cl2 affect the equilibrium of NOCl?

The addition of NO and Cl2 will shift the equilibrium towards the products (NOCl) according to Le Chatelier's principle. This is because the increase in the concentrations of reactants will cause the reaction to proceed in the forward direction to reach a new equilibrium.

3. What factors can affect the equilibrium of NOCl change with added NO and Cl2?

The equilibrium of NOCl change can be affected by changes in temperature, pressure, and concentrations of reactants and products. Presence of catalysts or inert gases can also affect the equilibrium.

4. How can the equilibrium of NOCl be manipulated?

The equilibrium of NOCl can be manipulated by changing the temperature, pressure, or concentrations of reactants and products. Adding a catalyst can also help to speed up the reaction and reach equilibrium faster.

5. How can the equilibrium constant (Kc) be calculated for the reaction between NO and Cl2?

The equilibrium constant (Kc) can be calculated by measuring the initial and equilibrium concentrations of NO, Cl2, and NOCl and plugging them into the equilibrium expression: Kc = [NOCl]^2 / [NO]^2[Cl2].

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