Equilibrium Constant Worksheet: Master Chemical Equilibria

6 min read 11-16-2024

Equilibrium Constant Worksheet: Master Chemical Equilibria

Chemical equilibria represent a dynamic state where the rates of the forward and reverse reactions are equal, leading to constant concentrations of reactants and products. Understanding the equilibrium constant (K) is crucial for mastering this concept. This article will explore various aspects of the equilibrium constant, how to calculate it, and provide a worksheet to facilitate learning.

What is the Equilibrium Constant?

The equilibrium constant (K) is a numerical value that expresses the ratio of the concentration of products to the concentration of reactants at equilibrium, each raised to the power of their respective coefficients in the balanced equation.

Mathematical Representation

For a general reaction:

[ aA + bB ⇌ cC + dD ]

The equilibrium constant expression (K) can be defined as:

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

Where:

[A], [B], [C], and [D] are the molar concentrations of the respective species.
a, b, c, and d are the coefficients from the balanced chemical equation.

Importance of the Equilibrium Constant

The equilibrium constant provides insights into the extent of a reaction:

K >> 1: The reaction favors products at equilibrium.
K << 1: The reaction favors reactants at equilibrium.
K ≈ 1: Significant amounts of both reactants and products are present.

Factors Affecting Equilibrium

Concentration: Changing the concentration of reactants or products will shift the equilibrium position.
Temperature: An increase or decrease in temperature can either favor the forward or reverse reaction depending on whether the reaction is exothermic or endothermic.
Pressure: For reactions involving gases, changes in pressure can affect the equilibrium position, favoring the side with fewer moles of gas.

Example Calculations of Equilibrium Constants

Let's explore a few examples to illustrate how to calculate the equilibrium constant.

Example 1: Simple Reaction

Consider the equilibrium reaction:

[ N_2(g) + 3H_2(g) ⇌ 2NH_3(g) ]

If the equilibrium concentrations are:

[N₂] = 0.5 M
[H₂] = 0.5 M
[NH₃] = 1.0 M

The equilibrium constant (K) can be calculated as follows:

[ K = \frac{{[NH_3]^2}}{{[N_2][H_2]^3}} = \frac{{(1.0)^2}}{{(0.5)(0.5)^3}} ]

[ K = \frac{1.0}{0.5 \times 0.125} = \frac{1.0}{0.0625} = 16 ]

Example 2: Shift in Equilibrium

Now, let’s examine what happens if the concentration of NH₃ is increased to 2.0 M while keeping the other concentrations constant.

The new K will still be calculated with the same formula:

[ K = \frac{{[NH_3]^2}}{{[N_2][H_2]^3}} = \frac{{(2.0)^2}}{{(0.5)(0.5)^3}} ]

[ K = \frac{4.0}{0.0625} = 64 ]

This demonstrates that K remains constant for a given temperature, but changes in concentrations can shift the equilibrium position.