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Equilibrium is a crucial part of the syllabus for students preparing for examinations. While there are many references to know in detail about this concept, very few offer its general characteristics.
So, today we bring all about equilibrium in physical processes, including the associated general characteristics. Let us start with clearing your doubts on equilibrium, different physical and chemical processes involving it, etc.
What is Equilibrium?
Equilibrium is the state of the process when the properties of the system like concentration, pressure, and temperature do not show any change with time. The equilibrium in physical and chemical processes is observed differently. If the equilibrium which develops between different phases or physical properties. In these processes, there is no change in chemical composition. It represents the existence of the same substance in two different physical states.
The main difference between equilibrium in physical and chemical processes is that in physical equilibrium, the physical state of the system does not change whereas chemical equilibrium is the equilibrium state in which the concentrations of reactants and products do not change with time.
Before going to the equilibrium in physical processes, it is important to understand the equilibrium in the chemical processes. In such processes, the two opposing processes occur at an equal rate. The mixture of reactants and products at the equilibrium state is the equilibrium mixture. It is represented as:
aA + bB = xX + yY
Here,
A, B are reactants
X, Y are products
chemical equilibrium, condition in the course of a reversible chemical reaction in which no net change in the amounts of reactants and products.
Equilibrium in physical procedure:
The equilibrium in physical processes between the different phases of physical states of matter is termed physical equilibrium. Thus, there are no changes in the chemical composition of the matter while it achieves physical equilibrium. Hence, the equilibrium of physical processes helps determine the general characteristics.
Types of equilibrium in physical procedure:
- Solid-liquid equilibrium
When some ice cubes and some water at zero degrees Celsius and average temperature are stored in a vacuum flask, the mass of ice and water is constant. The only condition is that no heat can leave or enter the vacuum flask which is the general characteristics of equilibria involving physical processes. Thus, at equilibrium:
Rate of melting ice = Rate of freezing of water
The average freezing point or melting point of the substance is the temperature at which the solid and liquid forms of the substance are at equilibrium at atmospheric pressure.
- Liquid-vapor equilibrium
It can be observed by monitoring the mercury levels in the manometer limbs attached to the system having an arrangement for the addition of liquid and evacuation. When the system is evacuated, the mercury is balanced in both limbs of the manometer. After adding water at the average room temperature, the mercury levels in the left limb start falling, and the level on the right limb starts to rise. With time, the mercury levels become constant, and hence the liquid-vapor equilibrium is attained.
Rate of evaporation = Rate of condensation
The higher vapor pressure liquid is more volatile and observes a lower boiling point.
- Solid- vapor equilibrium
The solids that undergo sublimation can achieve solid-vapor equilibrium. When solid iodine is placed in a closed vessel, it starts sublimation. The violet vapors start appearing in the closed vessel, and their intensity increases with time until equilibrium is attained.
Here, rate of sublimation of solid iodine to vapors = rate of condensation of iodine vapor to give solid iodine.
- Solid-solution equilibrium
When solid-like sugar is put in water, it starts dissolving completely. With an additional amount of sugar added in water, a stage comes one it stops dissolving and starts settling down at the bottom of the container. Such a condition indicates the solid-solution equilibrium.
Rate of dissolution = Rate of precipitation
The amount of dissolved sugar and the solution’s concentration remains constant.
- Gas-solution equilibrium
The best example of gas-solution equilibrium is observed in a soda water bottle. The gas pressure is very high above the liquid in a closed soda bottle, and hence the mass of gas dissolved is also high. Once a bottle is opened, the dissolved gas escapes as the pressure decreases atmospheric pressure and solubility.
General characteristics:
The six main characteristics of equilibrium in physical processes include:
- When the physical process reaches equilibrium, any observable property becomes constant.
- The physical equilibrium in gasses can be achieved in closed vessels only. This is because if the vessel is opened, the gasses will escape, and the physical process loses its equilibrium.
- The equilibrium in physical processes is dynamic as there are two opposing processes at equal rates.
- The concentration of the different substances participating in the physical process becomes constant and constant temperature at equilibrium.
- The equilibrium in physical processes involves an expression that gives the concentration of the different substances of matter.
- The equilibrium constant’s magnitude depends on the extent of the process achieved before the attainment of equilibrium.
Conclusion:
Hence it is easy to understand the basics of physical processes and the state of equilibrium. This state is observed in different physical and chemical changes or processes that make it easy to understand the nature of equilibrium. After clearing this concept, the details about the general characteristics of equilibrium can be drawn.
The equilibrium in physical processes is associated with multiple characteristic features. These features include conditions achieved during equilibrium, changes in the states to achieve a stable state, etc. The same substance in two different states makes it easy to verify these characteristics.
