# For the endothermic reaction N2O4(g) 2NO2(g) what is the effect of adding NO2 to the reaction vessel?

the reaction will shift left to right

the reaction will shift right to left

there will be no further reaction

what happens depends on the temperature

Relevance

N2O4 <====> 2 NO2

LeChatelier's Principle says that "when an EXTERNAL stress (pressure change, conc change, or temperature change) is applied to a chemical system that is in a state of equilibrium, then the equilibrium of the system will be upset, and the system will automatically respond so as to UNDO the stress applied externally."

So, at equilibrium, you have a specific ratio of NO2 to N2O4. When you upset that ratio (such as by adding NO2 to the sealed cell), the system will adjust the mix in the cell until that equilibrium ratio is restored.

So, for example, if you had 1.0 mole of N2O4 and 2.0 moles of NO2 in the cell at equilibrium, and then you pumped in another 1.0 moles of NO2, the system would adjust by combining NO2 molecules until you restored the 2:1 ratio, so that the cell would now contain 1.25 moles of N2O4 and 2.50 moles of NO2.

In a similar fashion, if you had the 1:2 mixture, and you pumped in an additional mole of N2O4, the system would adjust by dissociating N2O4 into NO2, and the end result would be 1.5 moles of N2O4 and 3 moles of NO2.

Cain has the correct answer, but it becomes a bit easier to understand with the equation written out. I hope this helps to clarify the situation.

Source(s): 35 years in chemistry
• Look at the equation

N2O4 <==> 2 NO2

the equilibrium constant, K = [NO2]^2/[N2O4] is always constant.

If you add NO2 to the vessel, more N2O4 has to be made from NO2 to maintain the equilibrium. This shifts the reaction to the left.

It is endothermic, meaning heat is consumed during the process. Adding heat will encourage the reaction - or shift it to the right.

• Gonna shift to the left. That reaction is an equilibrium, and LeChatlier's Principle states that when you stress a system at equilibrium, it changes or "moves" in a way to relieve that stress. Adding NO2 will send it to the left.

• According to Lechatliers principle: When a stress is placed on a system, the systems equilibrium will shift to the right or the left to reduce the effect of the stress. If you add to the concentration you increase the number of moles of the NO2 gas therefore it will shift to the left.