Equilibrium in physical processes and chemical processes

Introduction:

The term equilibrium refers to a system whose properties, such as pressure, concentration, and temperature, do not change over time. The equilibrium is called physical equilibrium when the opposing processes solely involve physical changes. On the other hand, chemical equilibrium exists when the opposite procedures entail chemical changes. At equilibrium, both opposing processes occur at the same time. An equilibrium mixture is the mixture of reactants and products that exists in a state of equilibrium.

Definition of Equilibrium:

Equilibrium is a state in which the macroscopic properties of the system remain unchanged. For instance, in a closed container, the water is in a state of equilibrium. The amount of molecules escaping from the water’s surface equals the number of molecules that enter. The rate of evaporation and condensation is the same, and the water and vapor are in a condition of equilibrium. Equilibrium mixture is the mixture of products (water in liquid form) and reactant (water in vapor form) in this condition. Here are some general characteristics of equilibria involving physical processes:

Properties of equilibrium involving physical processes:

• Only a closed system at a specific temperature may achieve equilibrium
• The rates of forward, as well as reverse reactions, are the same
• All measurable attributes of the system stay constant while the system is in equilibrium
• The equilibrium of a physical process depends on the constant value of one of its parameters, known as the equilibrium constant
• The concentration of chemicals becomes constant at constant temperature in an equilibrium state
• The value of the equilibrium constant indicates how far the reaction has progressed before reaching equilibrium

Types of equilibrium in physical processes:

• Phase Equilibrium:

At the temperature of 0°C, the number of water molecules that become ice is equivalent to the number of water molecules that melt to become liquid water. The rate at which water freezes is the same as that at which ice melts. As a result, there is a balance between solid ice and liquid water. Ice (solid) ⇌ Water (liquid) The number of molecules that become vapor in a closed container is equal to the number of molecules that condense into a liquid. Moreover, the pace at which liquid water evaporates is equivalent to the rate at which water vapor condenses. The liquid phase and its vapor phase are in balance. Water (liquid) ⇌ Water (gas)

• Solute-Solid Equilibrium:

When the solute of a saturated solution comes into contact with an undissolved solute, the number of molecules leaving the solution equals the molecules that enter the liquid from the solid. As a result, the undissolved solids and the solute in a solution are in equilibrium. Solute (aqueous) ⇌ Solute (solid)

• Gas-Liquid Equilibrium:

Gases not reacting with liquids dissolve in direct proportion to the liquid’s pressure. The gas inside and above the liquid is in equilibrium in a closed container. For example, the carbon dioxide gas in soft drinks is in equilibrium with the gas in the container’s empty space. Gas (solution) ⇌ Gas (gas)

Examples:

• At atmospheric pressure and 273K, ice and water achieve solid-liquid equilibrium
• At 1 atmosphere and 373 degrees Fahrenheit, liquid water and water vapours reach a state of equilibrium
• In a closed container, solid iodine and iodine vapors achieve solid-vapor equilibrium

Equilibrium in chemical processes or dynamic equilibrium:

You’ve probably heard of reversible reactions. Reversible reactions occur both forward and backward. When the rates of the forward and the reverse reactions are equal, the concentrations of products and reactions stay constant. The reaction is said to be in chemical equilibrium at this point. This equilibrium, however, is believed to have a dynamic nature. That’s because it has a forward reaction in which the reactants react to produce products and a reverse reaction in which the products can combine to yield the original reactants. In a closed vessel, hydrogen and iodine vapor is kept at a constant temperature. By converting some of the hydrogen and iodine to hydrogen iodide, the process continues for a short time before ending. That’s because the reactant and product reach equilibrium after this dynamic point. A fraction of hydrogen iodide is transformed into hydrogen and iodine molecules when placed in a closed jar at the same temperature. As a result, the remaining hydrogen iodide is unaffected. However, the amounts of hydrogen, iodine, and hydrogen iodide stay constant in both tests. It is said to have reached equilibrium when such a dynamic stage is reached. H₂ (g) + I₂ (g)⇌ 2HI (g)

Characteristics of Chemical equilibrium:

1) When the reactants and products are in equilibrium, their concentrations become constant. For example, pressure consistency in water evaporation, calcium carbonate breakdown, and colour constant at equilibrium in NO decomposition. 2) At equilibrium, the rate of the forward reaction equals that of the backward reaction, creating a dynamic equilibrium. 3) Chemical equilibrium occurs if none of the products disappears or separates as solids. 4) Chemical equilibrium can occur in either direction, i.e., towards the reactants or toward the products. 5) A catalyst does not affect the equilibrium state. A catalyst raises the speed of both the forward and backward reactions to the same level. Due to this, the equilibrium is not disturbed, and the concentrations of the reactants and products remain unchanged. Therefore, the catalyst has only one effect: it accelerates the process of reaching equilibrium.

Difference between:

Physical Equilibrium	Chemical Equilibrium
A physical equilibrium is a state of equilibrium in which the system’s physical structure does not change	Chemical equilibrium is a state of equilibrium where the concentrations of reactants and products stay constant with time
Physical equilibriums reveal that the physical states of the matter involved in the equilibria do not change	Chemical equilibrium shows that the proportions of the reactants and products involved in the procedure do not vary
The presence of two physical states inside the same closed system is called physical equilibrium	Forward and backward reaction rates are identical in chemical equilibrium

Conclusion:

The equilibrium state in a system is when all of the system’s parameters are constant. A physical equilibrium occurs when the physical condition of the system remains constant. On the other hand, chemical equilibrium occurs when the concentrations of reactants and products remain consistent over time.