# Question acd19

May 4, 2016

The concentration of nitrous oxide will decrease.

#### Explanation:

You are right, the position of the equilibrium will shift as a result of an increase in temperature.

As you know, equilibrium reactions are governed by Le Chatelier's Principle, which states that when a stress is placed on a system at equilibrium, the equilibrium will shift in a such as way as to reduce that stress.

Your starting equilibrium looks like this

2"NO"_ ((g)) + "H"_ (2(g)) rightleftharpoons "N"_ 2"O"_ ((g)) + "H"_ 2"O"_((g)) + color(red)("heat")

The fact that heat is located on the products' side tells you that you're dealing with an exothermic reaction, i.e. a reaction that gives off heat to the surroundings.

Now, you add a stress to the position of this equilibrium by adding heat.

How would the system counteract this added heat?

The position of the equilibrium will shift in such a way as to consume heat, since this will allow the equilibrium to be reestablished.

We've already established that the forward reaction

2"NO"_ ((g)) + "H"_ (2(g)) -> "N"_ 2"O"_ ((g)) + "H"_ 2"O"_((g)) + color(red)("heat")

is exothermic and thus produces heat, so the only way for the system to counteract the added heat is to favor the reverse reaction

${\text{N"_ 2"O"_ ((g)) + "H"_ 2"O"_ ((g)) + color(red)("heat") -> 2"NO"_ ((g)) + "H}}_{2 \left(g\right)}$

since this reaction consumes heat, i.e .is endothermic.

This means that the equilibrium will shift to the left

$\textcolor{w h i t e}{a}$

2"NO"_ ((g)) + "H"_ (2(g)) rightleftharpoons "N"_ 2"O"_ ((g)) + "H"_ 2"O"_((g)) + color(red)("heat")#

$\stackrel{\textcolor{b l u e}{\leftarrow}}{\textcolor{w h i t e}{a a a a a \textcolor{g r e e n}{\text{shift to the left}} a a a a a a a a}}$

So, what does this mean?

Nitrous oxide, $\text{N"_2"O}$, will react with water, $\text{H"_2"O}$, and take in some of that added heat to form nitric oxide, $\text{NO}$, and hydrogen gas, ${\text{H}}_{2}$.

Since some of the nitrous oxide will be consumed, its concentration will decrease.