EQUILÍBRIO QUÍMICO: Kc e Kp

Summary

In this engaging chemistry lesson, Gabriel Cabral introduces the concept of chemical equilibrium and the equilibrium constant (Kc and Kp). He explains how to calculate the equilibrium concentrations or partial pressures of products and reactants using formulas and coefficients. With a focus on gases, he demonstrates the process using examples, including the dimerization of NO2. The video aims to help students understand equilibrium calculations in chemical reactions, especially in the context of the ENEM exam, while encouraging viewers to subscribe for more lessons and resources.

Takeaways

• 😀 Chemical equilibrium constants help us understand the composition of substances at equilibrium.
• 😀 KC (constant of equilibrium) is calculated based on the concentration of products over reactants, raised to the power of their coefficients.
• 😀 For gaseous reactions, equilibrium is expressed using molar concentrations (mol/L) or partial pressures (atm).
• 😀 The equilibrium constant expression for concentration (KC) includes only gases and aqueous solutions, excluding solids and liquids.
• 😀 The general form of the equilibrium constant expression involves products raised to their respective coefficients, divided by reactants raised to theirs.
• 😀 When calculating the equilibrium constant from partial pressures (KP), the same principle applies but with pressures instead of concentrations.
• 😀 Temperature can affect the equilibrium constant, but it is the only factor that does so; changing pressure or concentration does not.
• 😀 To solve for unknown concentrations at equilibrium, we use the equilibrium constant and the known concentrations of reactants or products.
• 😀 In a given problem, if only one concentration is unknown, the equilibrium constant expression can be used directly to solve for it.
• 😀 Problems often involve dimerization or other chemical reactions at equilibrium, where the relationship between initial and equilibrium concentrations can be used to find missing values.

Q & A

What is the purpose of the equilibrium constant in chemistry?

The equilibrium constant (K) is a number experimentally determined that helps in calculating the composition of a chemical reaction at equilibrium. It gives insights into whether the reaction favors products or reactants.

What is the formula to calculate the equilibrium constant (Kc)?

The formula to calculate Kc is the concentration of the products raised to their respective coefficients, divided by the concentration of the reactants raised to their respective coefficients. This is expressed as Kc = [Products]^coefficients / [Reactants]^coefficients, where concentrations are measured in mol/L.

What is the difference between Kc and Kp?

Kc is the equilibrium constant expressed in terms of concentration (mol/L), whereas Kp is expressed in terms of partial pressure (atm) of gases involved in the reaction.

What units are typically used for the concentrations in the Kc expression?

Concentrations in the Kc expression are typically expressed in mol/L (moles per liter).

When calculating Kp, what is used instead of concentrations?

When calculating Kp, partial pressures of the gases are used instead of concentrations. These are typically measured in atmospheres (atm).

Why is the solid carbon not included in the equilibrium expression for certain reactions?

In equilibrium expressions, solids and liquids are not included because their concentrations do not change during the reaction. Only gases and aqueous solutions are considered since their concentrations can vary.

How does temperature affect the equilibrium constant?

Temperature is the only factor that can change the value of the equilibrium constant. Changes in temperature can shift the equilibrium position and alter the value of Kc or Kp.

What happens if the concentration of reactants is increased in a reaction at equilibrium?

If the concentration of reactants is increased, the reaction will shift towards the products to re-establish equilibrium, in accordance with Le Chatelier's principle.

How do you calculate the concentration of an unknown substance in equilibrium if you are given one known concentration?

You can use the equilibrium constant expression and substitute known values to solve for the unknown concentration. This typically involves solving algebraic equations, often requiring the use of quadratic equations or approximations.

What does a high value of the equilibrium constant (K) signify about the reaction?

A high value of K indicates that the reaction favors the formation of products at equilibrium, meaning there are more products than reactants in the system.