Chemical Equilibrium

Chemical Equilibrium

By

Dr. Luis Bello

​Chemical equilibrium is a state in a chemical reaction where the forward reaction rate is equal to the reverse reaction rate.

This means that the concentrations of the reactants and products are constant over time.

At equilibrium, the rate of the forward reaction is exactly balanced by the rate of the reverse reaction, resulting in no net change in the concentrations of reactants or products.

​Chemical equilibrium can be categorized into two types:

Homogeneous equilibrium:

In homogeneous equilibrium, all the reactants and products are in the same phase. For example, the reaction between nitrogen dioxide and dinitrogen tetroxide, 2NO2(g) ⇌ N2O4(g), is an example of homogeneous equilibrium because both reactants and products are gases.

Heterogeneous equilibrium: In heterogeneous equilibrium, the reactants and products are in different phases. For example, the reaction between calcium carbonate and calcium oxide,

CaCO3(s) ⇌ CaO(s) + CO2(g), is an example of heterogeneous equilibrium because the reactant calcium carbonate is a solid, while the products calcium oxide and carbon dioxide are a solid and a gas, respectively.

​Ionic equilibrium is a state in which the concentration of ions in a solution remains constant over time.

This state is reached when the rate of the dissociation of an ionic compound in the solution is equal to the rate of its recombination. Ionic compounds that dissolve in water form ions, which can either recombine to form the original compound or remain as separate ions in the solution.

Acid-base reactions also involve ionic equilibrium, where the concentration of the conjugate acid and base determines the strength of the acid or base. In this case, the equilibrium constant is known as the acid dissociation constant (Ka) or the base dissociation constant (Kb).

​In an ionic equilibrium, the concentration of ions in the solution is determined by the solubility product constant (Ksp) of the compound.

This constant describes the equilibrium between the dissolved ions and the undissolved compound. If the concentration of ions in the solution exceeds the Ksp value, then the excess ions will combine to form the solid compound. If the ion concentration is lower than the Ksp value, then the compound will continue to dissolve until equilibrium is reached.

​Le Chatelier's principle states that when a system at equilibrium is subjected to a change in temperature, pressure, or concentration of reactants or products, the system will shift its equilibrium position to counteract the change and re-establish equilibrium.

For example, if a system is at equilibrium and the concentration of one of the reactants is increased, the system will shift its equilibrium position to consume some of the added reactant, decreasing its concentration and bringing the system back to equilibrium.

Multiple Choice

dynamic equilibrium

• condition of continuous, random movement of particles but no overall change in concentration of materials

• the process by which one or more substances change to produce one or more different substances

• a condition where the reaction occurring in a system is completely halted and there exists no movement between the reactants and the products corresponding to the chemical reaction

• a substance that takes part in and undergoes change in a chemical reaction

Multiple Choice

This symbol indicates that a reaction is ____________

• reversible

• irreversible

Multiple Choice

When the rate of the forward reaction is equal to the rate of backward reaction, the system is said to be in

• Chemical Equilibrium

• Chemical Balance

• Chemical Constant

• Chemical Reaction

Multiple Choice

At what time does the reaction reach equilibrium?

• t₁

• t₂

• t₃

• t₄

Multiple Choice

It is a chemical reaction where the reactants form products and the products form reactants.

• reversible reaction

• nonreversible reaction

• decomposition reaction

• standard reaction

Multiple Choice

Identify the labels (a) and (b) on the graph.

• a is the amount (concentration) of reactants and b is the concentration of products

• a is the amount (concentration) of products and b is the concentration of reactants

• a is the volume of reactants and b is the volume of products

• a is the mass of reactants and b is the mass of products