Equilibrium Constant K - Online Tutor, Practice Problems & Exam Prep

Understanding the equilibrium constant (K) is crucial for predicting the direction of a chemical reaction. K indicates whether the products or reactants are favored when a reaction reaches equilibrium, which is a state where the forward and reverse reactions occur at the same rate. A K value greater than one suggests the forward reaction is favored, producing more products, while a K less than one indicates a preference for the reverse reaction, yielding more reactants. If K equals one, neither direction is favored, and the concentrations of products and reactants are equal.

The equilibrium constant is derived from the ratio of the concentrations of products to reactants, raised to the power of their respective coefficients in the balanced chemical equation. However, solids and pure liquids are excluded from this expression as their concentrations do not change with pressure and are not included in the K expression. The equilibrium constant is also temperature-dependent, altering its value with temperature changes.

Furthermore, the relationship between the equilibrium constant and the rate constants of the forward and reverse reactions (represented by lowercase k) is given by the equation:

K=k_forward/k_reverse The rate constant, unlike the equilibrium constant, includes time in its units, indicating the speed of the reaction. This distinction between K and k is essential for a comprehensive understanding of how chemical reactions work.

Equilibrium Constant Expressions

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 forward 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 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 see 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 a units. Here time could be in seconds, inverse days, inverse years, inverse any unit of time.

So just remember looking at a chemical reaction to get the complete picture, we look at the equilibrium constant K to determine its direction, and we look at the rate constant k to determine the speed of which it proceeds.

Equilibrium Constant Expressions

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_EQ. And we're going to say that it represents a ratio of product to reacting concentrations at equilibrium. We're going to 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 going to 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 are 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 K's. So throughout this course, we'll be looking at different types of K's. For now, we're going to be concerned with K_P and K_C. K_P is used when our concentration units are in atmospheres and K_C 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 we do our equilibrium expression which is represented by this portion. We would not include solids and liquids. We're going to 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 what we don't include them within our equilibrium expressions.

Alright, 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 2 moles of water as a liquid and magnesium chloride aqueous. Remember, we don't include solids and liquids, so these are going to be excluded. We're going to 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 2, so we put a 2 here. This here would represent the equilibrium expression for the chemical balance chemical reaction given above.

K = [ MgCl 2 ] [ HCl 2 ]

Equilibrium Constant K Example

What is the equilibrium constant expression for the following reaction? Now remember, with equilibrium expressions we exclude solids and liquids. If we take a look here, here's a solid. So we're going to exclude this exclude, exclude and exclude.

We're going to say our equilibrium expression K or equilibrium constant K equals products over reactants. So the products over reactants represents our equilibrium expression we're going to include here we have the concentration of hypochlorous acid HOCL and then here we have CL₂ chlorine gas.

Remember their coefficients will be our exponents and since both of them have a coefficient of two, this will be hypochlorous acid squared over CL₂ gas also squared. This here represents the equilibrium expression for the chemical reaction given within this example question.

K = [ HOCl ] 2 [ Cl 2 ] 2

Provide K expression for the reverse of the following reaction:

Fe₂O₃(s) + 3 H₂(g) ⇌ 2 Fe(s) + 3 H₂O(g)

• A.
• B.
• C.
• D.

Magnitude of Equilibrium Constant

Here we say that the magnitude of our equilibrium constant K indicates how far to the left or to the right a reaction lies at 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 1.

When K is greater than one, we're going to say here that our products and the forward reaction are favored. Remember K is products over reactants. Here we could say for example the amount of products is equal to 10, our amount of reactions equal to two. So overall K=5. We can see that there's more product than reactant. 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 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 1, then neither direction is favored. OK, so you're making the same amount of reactants and products. So here K would be equal to 1. 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 forward direction divided by the rate constant of the reverse direction or a reaction. So again, capital K is the equilibrium constant. Lower case 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 1 where neither side is really favored over the other? They're both equal.

Equilibrium Constant K Example

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 chapter 4 reacting with two moles of H₂S to produce. We have here CS₂ and H₂. We're told that our equilibrium constant in the form of K_P is 1.3×103.

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 forward direction is favored. So the side that's favorite are our products, which means we're making more of them. And when it comes to the pressure of gases, the more particles or molecules of gases 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.

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

• A. 2 NO(g) ⇌ N₂(g) + O₂(g) K_eq = 2.4 x 10³⁰
• B. 2 NO₂(g) ⇌ 2 NO + O₂(g) K_eq = 5.8 x 10^–5
• C. 2 CO₂(g) ⇌ O₂(g) + 2 CO(g) K_eq = 3.1 x 10^–5
• D. 2 H₂O(g) ⇌ 2 H₂(g) + O₂(g) K_eq = 5.1 x 10^–82

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?

• A. partial pressure of A
• B. partial pressure of B & C
• C. partial pressures will be equal

Here’s what students ask on this topic:

What is the equilibrium constant?

The equilibrium constant, denoted as K_eq or just K, is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium for a reversible chemical reaction at a constant temperature. It provides a quantitative measure of the position of equilibrium and indicates the extent to which a reaction proceeds.

For a generic chemical reaction where aA + bB → cC + dD, the equilibrium constant expression is written as:

$K=\frac{{\left[C\right]}^c{\left[D\right]}^d}{{\left[A\right]}^a{\left[B\right]}^b}$

Here, [A], [B], [C], and [D] represent the molar concentrations of the reactants and products at equilibrium, and a, b, c, and d are the stoichiometric coefficients from the balanced chemical equation.

If K is much greater than 1, the reaction favors the formation of products. If K is much less than 1, the reaction favors the reactants. If K is close to 1, significant amounts of both reactants and products are present at equilibrium. It's important to note that the equilibrium constant is only affected by temperature changes and is independent of the

Which expression represents the correct equilibrium constant for the reaction below?

To provide an accurate response to your question, I would need the specific chemical reaction you're referring to. The equilibrium constant expression depends on the balanced chemical equation for the reaction.

However, I can explain how to write the equilibrium constant expression for a general reaction. For a reaction where the reactants A and B form the products C and D:

aA + bB → cC + dD

The equilibrium constant expression (K) for this reaction is written in terms of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients:

K = [C]^c[D]^d / [A]^a[B]^b

Here, [A], [B], [C], and [D] represent the molar concentrations of A, B, C, and D, respectively, at equilibrium. The letters a, b, c, and d are the stoichiometric coefficients from the balanced equation.

Remember that only gases and aqueous solutions are included in the expression. Pure solids and pure liquids do not appear in the equilibrium constant expression. If you provide the specific reaction, I could give you the exact form of the equilibrium constant for that reaction.

What is the equilibrium constant expression for the given system?

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To write the equilibrium constant expression for a given chemical system, you need to follow the law of mass action. This law states that at a constant temperature, the equilibrium constant (K) for a reversible reaction is the ratio of the product of the concentrations of the products raised to the power of their stoichiometric coefficients to the product of the concentrations of the reactants raised to the power of their stoichiometric coefficients.

For a general reaction:

$aA+bB\rightleftharpoons cC+dD$

The equilibrium constant expression (K<sub>c</sub>) is written as:

$K{c}_{}=\frac{\left[C\right]{}^c\left[D\right]{}^d}{\left[A\right]{}^a\left[B\right]{}^b}$