Effect of an Inert Gas on Equilibrium

In summary, the addition of an inert gas in a container at constant volume and temperature will not change the concentrations of N2O4 and NO2 if expressed in molarity. However, if expressed as a molar fraction or mass fraction, the concentrations will decrease. This does not affect the equilibrium constant, which is governed by partial pressures that remain constant. Therefore, the correct answer is B, as the pressure of the system increases, leading to a higher concentration of chemicals and a shift in equilibrium to the left to restore the original ratio of concentration to volume.
  • #1
brbrett
35
0

Homework Statement


N2O4(g) + energy <---> 2NO2(g)

How are Keq and [N2O4] affected by the addition of Ne, an inert gas, in a container at constant volume and temperature.
Keq [N2O4]
a) no change/no change
b) no change/ increases
c) increases/decreases
d) decreases/increases

Homework Equations


n/a

The Attempt at a Solution


I got an answer of A, however the correct answer is apparently B. If my understanding is correct, B is the correct answer because the pressure of the system has increased, therefore increasing the chemicals to a higher concentration. Equilibrium will be shifted left to attempt to restore the original ratio of concentration to volume.

Is this reasoning correct? I did some research on the internet, and a lot of people say the addition of an inert gas will not change concentrations if the volume is constant, just like this question. Also, Keq will not change regardless, as mathematically nothing has changed since the concentrations rise and fall in proportion with their molar ratios.
Thank you once again~
 
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  • #2
It depends on how you express concentration.

If as molarity - inert gas doesn't matter, "a" is the answer. Just take a look at the molarity definition - everything remains constant.

If as a molar fraction or a mass fraction (percentage) - then definitely concentrations go down. It doesn't matter for the equilibrium, as this is governed by partial pressures which remain constant.

No idea why the answer "a" is not accepted as a correct one though, if the question doesn't state what concentration type to use.
 

What is the effect of an inert gas on equilibrium?

The presence of an inert gas in a reaction does not affect the equilibrium position or the value of the equilibrium constant. It only changes the partial pressures of the reactants and products.

Why is an inert gas used in equilibrium reactions?

Inert gases, such as helium or argon, are used to increase the total pressure of the system without affecting the equilibrium. This allows for a greater number of collisions between reactant molecules, which can speed up the reaction.

Can an inert gas shift the equilibrium in a reaction?

No, an inert gas does not have any effect on the equilibrium position. It only changes the partial pressures of the reactants and products. Only changes in temperature, pressure, or concentration of reactants and products can shift the equilibrium.

How does an inert gas affect the equilibrium constant?

The presence of an inert gas does not change the value of the equilibrium constant. The equilibrium constant is a function of temperature and is not affected by changes in pressure or the addition of an inert gas.

Can an inert gas be used to manipulate the equilibrium of a reaction?

No, an inert gas is not capable of manipulating the equilibrium of a reaction. It can only affect the partial pressures of the reactants and products, which does not change the equilibrium position or the value of the equilibrium constant.

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