yego.me
💡 Stop wasting time. Read Youtube instead of watch. Download Chrome Extension

Worked example: Using Le Chȃtelier’s principle to predict shifts in equilibrium | Khan Academy


3m read
·Nov 10, 2024

Carbon monoxide will react with hydrogen gas to produce methanol. Let's say that the reaction is at equilibrium, and our job is to figure out which direction the equilibrium will shift: to the left, to the right, or not at all. As we try to make changes to the reaction at equilibrium, for example, if we add some hydrogen gas to our reaction at equilibrium, we're increasing the concentration of one of our reactants. According to Le Chatelier's principle, the net reaction will move in the direction that decreases the stress placed on the system.

So, if the stress is increased in the amount of one of the reactants, the equilibrium will shift to the right to get rid of some of that reactant. In part B, some methanol is removed, so for decreasing the concentration of our product, the equilibrium is going to shift to make more of our product. Therefore, the equilibrium will shift to the right.

Next, the volume is increased in the reaction at equilibrium. If we increase the volume, we decrease the pressure; therefore, we could consider the stress to be decreased pressure. Le Chatelier's principle says the net reaction is going to go in the direction that relieves the stress. So, if the stress is decreased pressure, the net reaction is going to shift to increase the pressure, and we can figure out which direction that is by looking at the balanced equation.

On the reactant side, there's one mole of gas and two moles of gas for a total of three moles of gas. On the product side, there's only one mole of gas. So, there are three moles of gas on the left and only one mole of gas on the right. Since the net reaction is going to try to increase the pressure, the equilibrium shifts to the left toward the side that's going to form more moles of gas, therefore increasing the pressure.

Next, we try adding some neon gas to our reaction mixture at equilibrium. Well, neon gas is an inert gas, which means it doesn't react with any of our reactants or products. If we look at the expression for the reaction quotient, Qp, neon gas is not included. Therefore, adding neon gas is not going to change the value for Qp, so the reaction remains at equilibrium.

So, the answer is there's no shift when an inert gas is added. That might sound a little strange at first because adding neon gas means that the total pressure would increase since you're adding a gas. However, the partial pressures stay the same. So, the partial pressures for methanol, carbon monoxide, and hydrogen gas actually stay the same; and therefore, Q doesn't change.

Next, we add a catalyst to our reaction at equilibrium. Catalysts speed up reactions by lowering the activation energy. However, the catalyst is going to speed up the forward and the reverse reactions by the same amount, and therefore the reaction remains at equilibrium. So, there's no shift when a catalyst is added to a reaction at equilibrium.

Then, in part F, let's try decreasing the temperature in the reaction at equilibrium. Well, this reaction is exothermic because delta H is less than zero, so we can treat heat as a product. So, we go ahead and write heat on the product side. If we treat heat like a product, decreasing the temperature is like decreasing the amount of our product. Therefore, the net reaction will move to the right to make more of the product.

When that reaction moves to the right, you can think about that being an increase in the amount of products and, therefore, a decrease in the amount of reactants. When you increase the products and decrease the reactants, you increase the value for the equilibrium constant. Therefore, lowering the temperature causes an increase in the equilibrium constant for an exothermic reaction.

Note that changing the temperature in part F is the only change that actually changed the equilibrium constant. So, in all the other ones, in A through E, the equilibrium constant stayed the same value.

More Articles

View All
The 6 BEST Purchases To Make In Your 20s
What’s up guys? It’s Graham here. So don’t ask me how this happened, but this morning I got insanely sidetracked looking through all of my previous YouTube videos, and wow, I talked a lot about the worst things that have happened to me. If you don’t belie…
Charlie Munger's Alibaba Confession at the Daily Journal Annual Meeting (2023)
This video is sponsored by Morning Brew. Sign up to their free daily newsletter via the link in the description. I regret Alibaba’s one of the worst mistakes I ever made. I got over charmed by the people who were leading in the online retailing, and I di…
Assignment: Inspiration Winner | National Geographic
[Applause] After three uplifting photographic quests, our assignment inspiration finalists pitched us their photos, hoping to be the ones chosen to go on assignment with National Geographic Travel. We judges had an incredibly tough decision to make. Each …
Carl Sagan Tried To Warn You
Flowers are blooming in Antarctica. There are two species of flowering plants on the continent: the Antarctic hairgrass and the Antarctic Pearl wart, and they’re both growing at a much faster rate than ever before. In a study published by the University o…
9 Money Habits Keeping You Poor
What’s up guys, it’s Graham here. So, ever since I was a kid, I’ve been fascinated with the secrets of what makes somebody financially successful. To be honest, I really just wanted to figure out why some people were good with money versus why others were…
Renewable and Nonrenewable Energy Resources | AP Environmental Science | Khan Academy
Today, let’s talk about energy resources. You’ve probably already done something today that used energy resources, even beginning from the moment you woke up. For me, the beginning of my day always starts with making tea. I use energy in every step of thi…