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
How To Travel The World For Free: Credit Cards 101
What’s up you guys? It’s great in here. So, I realized the title of this video sounds like I’m about to pitch you on some weird timeshare opportunity in the Bahamas, and all you got to do is sit through an exciting two-hour seminar to unlock your free rew…
Charlie Munger’s Final Warning for Investors in 2024
It’s a radically different world from the world we started in. I think it’s going to get tougher. That was Charlie Munger speaking at the Berkshire Hathaway shareholders’ meeting earlier this year. I was there, sitting alongside tens of thousands of peopl…
Buddha - Be Aware, Become Free
In The Dhammapada, Buddha says, “the monk who delights in awareness, seeing the danger in unawareness, not liable to fall back, is close to [Nirvana].” So Buddha is saying that awareness leads to freedom from suffering, and unawareness leads to suffering.…
One Step at a Time | Life Below Zero
Long walk on a cold day. Thing I’ve learned about injuries is listen to your body. If your body’s hurting, it’s trying to tell you something. In this case right here, this leg’s trying to tell me not to use it. Just got to take it easy, take it one step …
YouTube On the Rise Contest- Smarter Every Day
Hey, it’s me Destin, I just got home from work. Ignore the thunderstorm in the background. But a couple of things I’d like to do after a long day at work is— the first is I find my wife and plant a big kiss on her. And then I take my boots off. That’s wha…
It’s Over: Why The Housing Market Is Screwed
What’s up, Grandma’s guys here! So, every now and then I see something that makes me lose absolutely all of my faith in my fellow millennial generation, because a new study just found that Millennials are more likely to water their house plants than think…