chem lecture march 12

Introduction to Equilibrium

• Equilibrium is a fundamental concept in chemistry that signifies a state of balance in chemical reactions.

• It is described as a condition where there is no net change in the concentrations of reactants and products, even though reactions occur in both directions.

Importance of Equilibrium

• Intuitive Concept: Equilibrium is generally well-understood and is a major topic throughout the semester.

• Relevance: Knowledge of equilibrium is crucial as it applies not only in chemistry but is also important in related fields like biochemistry and biological systems.

• Impact: Equilibrium concepts affect various properties such as vapor pressure, making solutions, and are vital for understanding chemical behaviors.

Dynamic Nature of Equilibrium

• At dynamic equilibrium:

  • Reactions continue to occur; however, the concentrations of reactants and products remain constant.

  • Reactions reach a point where the rate of conversion of reactants to products equals the rate of conversion of products to reactants.

  • This results in fewer collisions over time, causing a decrease in reaction rates until stabilization.

Chemical Equilibrium Constant (K)

• The equilibrium constant, denoted as K, quantifies the relationship between the concentrations of products and reactants at equilibrium.

• Mathematical Representation:

  • For a given reaction, K is represented as:[ K = \frac{[products]}{[reactants]} ]

  • Each concentration is raised to the power of its coefficient from the balanced chemical equation.

Types of Equilibrium Constants

– Kc vs. Kp:

• Kc: The equilibrium constant when all concentrations are expressed in molarity (mol/L).

• Kp: The equilibrium constant when dealing with gases, expressed in terms of partial pressures (e.g., atmospheres, mmHg).

Stoichiometry in Equilibrium

• When analyzing chemical equations:

  • Identify the stoichiometric coefficients which illustrate the ratio of reactants to products.

  • For example, for the reaction of sulfur dioxide (SO2) and oxygen (O2) producing sulfur trioxide (SO3), one must consider the molar ratios during the calculation of concentrations.

• Ensuring proper stoichiometric representation is crucial for obtaining correct equilibrium concentrations and understanding the dynamic equilibrium.

Common Misconceptions

• It is important to understand that:

  • The concentrations of products and reactants do not remain equal at equilibrium; they reflect specific proportions determined by the stoichiometry.

  • The K value remains constant unless temperature changes, regardless of the concentration changes of reactants and products.