Chemical Equilibrium Concepts and Applications

Chemical Equilibrium Concepts and Applications

Chemical equilibrium is a fundamental concept in chemistry that describes the state of a reversible reaction when the rates of the forward and reverse reactions are equal. This lecture covers key principles such as dynamic equilibrium, the equilibrium constant (K), and the factors affecting equilibrium, including concentration, pressure, and temperature changes. Designed for students studying general chemistry, it provides a comprehensive overview of the laws governing chemical reactions. The material includes practical applications and examples to illustrate how equilibrium concepts are used in real-world scenarios.

Key Points

  • Explains dynamic equilibrium and its significance in reversible reactions.
  • Details the equilibrium constant (K) and its relationship to reaction concentrations.
  • Covers the effects of concentration, pressure, and temperature on chemical equilibrium.
  • Introduces the ICE table method for calculating equilibrium concentrations.
  • Mahi Patel
118
/ 10
Assumptions About Reactions Thus Far…
● Recall stoichiometry from Chapter 7 → N2(g) + 3 H2(g) → 2 NH3(g)
● Up until this point (and without knowing it) we’ve been making the assumptions that:
1. The reaction only goes in the direction indicated by the equation
2. Completion of the reaction occurs when the limiting reactant(s) is completely
consumed
a. i.e., only products remain and absolutely no reactants are left (assuming all
reactants were limiting’
Reversible Reactions
● The truth is that many reactions are reversible
● Some reactions may be reversible to such a small extent that they would appear
un-reversible to the naked eye
Dynamic Equilibrium
● Dynamic equilibrium = the condition in which the rate of the forward reaction equals
the rate of the reverse reaction
● The concentrations of the product(s) and the reactant(s) no longer change
○ On the molecular level, however, both reactions continue to occur
● Both products AND reactants are present (to some extent)
What Equilibrium Is NOT
● It is NOT a ceasing of molecular activity
○ The reactions do not stop!
● It is NOT a state where all of the concentrations are the same
○ At equilibrium, [reactants] ≠ [products] !!
○ In fact, in the vast majority of the cases, the concentrations are different
● The concentrations of reactants and products at equilibrium can be experimentally
measured and used to define an EQUILIBRIUM CONSTANT (K)
The Equilibrium Constant (K) and Equilibrium Expression
● Equilibrium constant = the ratio AT EQUILIBRIUM of the concentrations of the
products raised to their stoichiometric coefficients divided by the concentrations of
reactants raised to their stoichiometric coefficients
○ It gives the relative concentrations of products and reactants present at
equilibrium
○ The relationship between the expression for K and the balanced chemical
equation is called the law of mass action
aA + bB ⇌ cC + dD
● The value of K for a given reaction reflects the extent to which that reaction goes in the
forward direction to achieve equilibrium
● Numerically large values of K = the forward reaction is strongly
favored
○ At equilibrium, products are favored over reactants and
relatively more products will be present in the equilibrium
mixture
○ Numerator bigger
● Numerically small values of K = the reverse reaction is strongly
favored
○ At equilibrium, reactants are favored over products
○ Denominator bigger
● Intermediate values of K = significant amounts of both reactants and products will be
present in the equilibrium mixture
○ The reaction has no significant preference in going in either direction
● For gas phase reactions the pressures at equilibrium can be used in place of
concentrations (more on this…)
● The value of K depends on temperature and stoichiometry
○ If you change T, you change the value of K
● For a given temperature, the equilibrium constant will always be the same regardless of
the initial concentrations of reactants and/or products
○ If a reaction is not at equilibrium, it will react in the direction that will lead it to
equilibrium
The Dependence of K on the Balanced Reaction
/ 10
End of Document
118
You May Also Like

FAQs of Chemical Equilibrium Concepts and Applications

What is dynamic equilibrium in chemical reactions?
Dynamic equilibrium occurs in a reversible reaction when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. This state does not imply that the reactions have stopped; rather, both reactions continue to occur simultaneously. Understanding dynamic equilibrium is crucial for predicting how changes in conditions will affect the system.
How is the equilibrium constant (K) calculated?
The equilibrium constant (K) is calculated by taking the ratio of the concentrations of the products raised to their stoichiometric coefficients divided by the concentrations of the reactants raised to their stoichiometric coefficients at equilibrium. This constant provides insight into the extent of the reaction and whether products or reactants are favored at equilibrium. A large K value indicates a reaction that favors products, while a small K value suggests a preference for reactants.
What factors can shift a chemical equilibrium?
Several factors can shift a chemical equilibrium, including changes in concentration, pressure, and temperature. According to Le Chatelier's Principle, if a system at equilibrium is subjected to a change, the system will adjust to counteract that change and restore equilibrium. For example, adding a reactant will shift the equilibrium towards products, while increasing temperature in an exothermic reaction will favor the reactants.
What is the ICE table and how is it used?
The ICE table is a systematic method used to calculate the concentrations of reactants and products at equilibrium. ICE stands for Initial, Change, and Equilibrium, representing the initial concentrations, the changes that occur as the system approaches equilibrium, and the final equilibrium concentrations. This tool helps in visualizing the stoichiometric relationships in a reaction and is essential for solving equilibrium problems.
How do concentration changes affect equilibrium?
Changes in concentration of reactants or products can significantly affect the position of equilibrium. If a reactant is added, the system will shift to the right, favoring the formation of products to re-establish equilibrium. Conversely, if a product is removed, the equilibrium will shift left to produce more of that product. This principle is essential for understanding how chemical reactions can be manipulated in industrial processes.

Related of Chemical Equilibrium Concepts and Applications