Equilibrium Constant K - Video Tutorials & Practice Problems

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Equilibrium Constant Expressions

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Hey, everyone the equilibrium constant, which is depicted as capital K specifies the favored direction of a reaction. Remember with chemical equilibrium, we're talking about reversible reactions. So we're talking about is the four direction favored or the reverse direction favored. While the equilibrium constant talks about direction, our rate constant, which is depicted by lower case K deals with the speed of our chemical reaction here. When we say rate constant, we're talking about uh chemical kinetics. So we're looking at how fast a chemical reaction proceeds. How quickly can my reactants break down to provide me products here? When we say our equilibrium constant K, it typically is connected to our concentration units. But when we talk about our rate constant, it's not only concentration but also time as the units here, time could be in seconds, inverse days in verse years in verse any unit of time. So just remember looking at a chemical reaction to get the complete picture, we look at the equilibrium constant capital K to determine its direction. And we look at the right constant lowercase K determine the speed at which it proceeds

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Equilibrium Constant Expressions

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Accompanying the equilibrium constant is the idea of equilibrium expressions. Now, first, we're going to say that our equilibrium constant K can be represented by capital K or capital K sub eq. And we're going to say that it represents a ratio of product to react in concentrations at equilibrium. We're gonna say that the equilibrium constant is temperature dependent. So if we change the temperature that's going to change the value of our equilibrium constant K. Now, here we've talked about expressions. But what exactly does that mean if we take a look here, we're gonna say we have our chemical reaction represented by our reactants A and B and our newly formed products C and D with them, we have different coefficients. So the numbers that go in front, we're going to say that our equilibrium constant again is a ratio of products to reactants. So it's products over reactants and it equals the concentrations of our products. And notice here that our coefficients are the exponents involved. So here X coefficients A and B are the exponents involved. Here, we're going to say that our equilibrium constant is known as an umbrella term. So it's just K but we can break it down into further types of cases. So throughout this course, we'll be looking at different types of KS for. Now, we're gonna be concerned with KP. And KCKP is used when our concentration units are in atmospheres and KC will be used when our concentration units are in molarity. Now, talking about our chemical reaction, we need to remember that solids and pure liquids are not or ex they, they are excluded. So they're excluded from our K expressions. So when we do our equilibrium expression, which is represented by this portion, we would not include solids and liquids. We're gonna say here that adding a solid or a pure liquid does not change their concentrations, they're unaffected by external factors such as pressure. So that's typically why we don't include them within our equilibrium expressions. All right. So let's try to set up an equilibrium expression for the equation given below. In this equation given below, we say that magnesium hydroxide solid reacts with two moles of hydrochloric acid to produce two moles of water as a liquid and magnesium chloride aqueous. Remember we don't include solids and liquids. So these are gonna be excluded. We're gonna have here K equals products over reactants. So here we have the concentration of magnesium chloride and then here we have the concentration of hcl hydrochloric acid because it's a reactant. Remember the coefficient forms the exponent the coefficient here is just one. So we don't need to include it, it's understood as being there. But the coefficient here for hydrochloric acid is two. So we put a two here, this here would represent the equilibrium expression for the chemical balance, chemical reaction given above.

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Equilibrium Constant K Example

Magnitude of Equilibrium Constant

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Here we say that the magnitude of our equilibrium constant K indicates how far to the left or to the right a reaction lines in equilibrium. Remember that overall value of K though is also based at a given temperature because remember equilibrium constant K is temperature dependent. When we're talking about the magnitude of our equilibrium constant, we're referring to K being either greater than one, less than one or equal to one. When K is greater than one, we're going to say here that our products and the forward reaction, our favorite, remember K is products over reactants. Here, we could say for example, the amount of product is equal to 10, our amount of reaction is equal to two. So overall K equals five, we can see that there is more product than reacted. Why would there be more product? Because we're moving in the forward direction to create it. Conversely, if we're going the opposite way, if K is less than one, this would mean the opposite where reactants now are more favored and which direction would we have to uh lead or move into? So that more reactants are created the reverse direction. So the reverse reaction would be favored. Here, we'd have 10 reactants to just two products giving us a K less than one. But let's say K is equal to one. Well, if K is equal to one, then neither direction is favored. OK. So you're making the same amount of reactants and products. So here K would be equal to one. Now, in addition to this, we can say that the magnitude of K can also be determined from your rate constants. And remember you have your rate constant, which is lower case K and it could be for the forward or the reverse of reactions for now, just realize that the connection between your equilibrium constant and your rate constants is given by this equation where your equilibrium constant K equals the rate constant of the four direction divided by the rate constant of the reverse direction or reaction. So again, capital K is your equilibrium constant, lowercase K is your rate constant. So when we're talking about magnitude, it just means what side is more favored forward side to make more product or reverse side to make more reactants or does K equal one where neither side is really favored over the other? They're both equal.

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Equilibrium Constant K Example

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In the following example, question, it says when this reaction comes to an equilibrium, which will be higher in pressure reactants or products. So here we have two moles of CH four reacting with two moles of H two S to produce. We have here, CS two and H two, we're told that our equilibrium constant in the form of KP is 1.3 times 10 to the third. Here, we can see that K is greater than one. Remember when K is greater than one, we say that the product side is favored and the four direction is favored. So the side that's favored are our products, which means we're making more of them. And when it comes to the pressure of gasses, the more particles or molecules of gas is present, the higher the pressure, since we have more products being favored, they would have an overall greater pressure. This would mean that out of all of our options, option B is the correct choice. Product side is favored. There's more products. Therefore, they will result in higher pressure.

Problem

Which of the reactions is likely to produce more O₂ at equilibrium at 25°C?

2 NO(g) ⇌ N₂(g) + O₂(g) K_eq = 2.4 x 10³⁰

2 NO₂(g) ⇌ 2 NO + O₂(g) K_eq = 5.8 x 10^–5

2 CO₂(g) ⇌ O₂(g) + 2 CO(g) K_eq = 3.1 x 10^–5

2 H₂O(g) ⇌ 2 H₂(g) + O₂(g) K_eq = 5.1 x 10^–82

Problem

Consider the reaction A(g) ⇌ B(g) + C(g), with k_forward of 5.7 x 10^–2 and k_reverse of 3.8 x 10^–4. Which would be greater at equilibrium, partial pressure of A or partial pressures of B and C?

partial pressure of A

partial pressure of B & C

partial pressures will be equal

Equilibrium Constant K - Video Tutorials & Practice Problems | Channels for Pearson+ (2024)

Equilibrium Constant Expressions

Equilibrium Constant Expressions

Equilibrium Constant K Example

Magnitude of Equilibrium Constant

Equilibrium Constant K Example

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