Equilibrium in physical processes is a fundamental concept in physics and chemistry that describes the state in which all competing influences are balanced. Understanding equilibrium is crucial for students as it forms the basis for advanced topics in thermodynamics and chemical kinetics. In these notes, we will cover types of equilibrium, conditions for equilibrium, and specific examples of equilibrium in various physical processes.
1. Types of Equilibrium
Equilibrium can be classified into two main types:
Static Equilibrium:
Definition: Static equilibrium occurs when an object is at rest, and all the forces acting on it are balanced.
Conditions: For an object to be in static equilibrium, the following conditions must be met:
The sum of all forces acting on the object must be zero (∑→F= 0)
The sum of all torques acting on the object must be zero (∑τ=0).
Dynamic Equilibrium:
Definition: Dynamic equilibrium occurs when an object is in motion but the net force and net torque acting on it are zero, resulting in a constant velocity.
Conditions: For an object to be in dynamic equilibrium:
The sum of all forces acting on the object must be zero (∑F= 0).
The sum of all torques acting on the object must be zero (∑τ= 0).
2. Conditions for Equilibrium:
For an object or system to be in equilibrium, the following conditions must be satisfied:
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Translational Equilibrium:
Net Force: The vector sum of all external forces acting on the system must be zero.
∑F= 0
Application: This condition ensures that the object does not experience any linear acceleration and remains at rest or moves with a constant velocity.
Rotational Equilibrium:
Net Torque: The sum of all external torques about any axis must be zero.
∑τ= 0
Application: This condition ensures that the object does not experience any angular acceleration and either remains at rest or rotates with a constant angular velocity.
3. Equilibrium in Physical Processes
Thermal Equilibrium:
Definition: Thermal equilibrium is achieved when two or more objects in thermal contact no longer exchange heat, meaning they have reached the same temperature.
Zeroth Law of Thermodynamics: If two systems are each in thermal equilibrium with a third system, then they are in thermal equilibrium with each other.
Chemical Equilibrium:
Definition: Chemical equilibrium occurs when the rate of the forward chemical reaction equals the rate of the reverse reaction, resulting in constant concentrations of reactants and products.
Equilibrium Constant (Keq): A numerical value that characterizes the ratio of the concentrations of products to reactants at equilibrium.
Keq = [C]c [D]d/
where [A], [B], [C], and [D] are the equilibrium concentrations of the reactants and products, and (a), (b), (c), and (d) are their stoichiometric coefficients.
Mechanical Equilibrium:
Definition: Mechanical equilibrium is achieved when an object is either at rest or moving with a constant velocity with no net force acting on it.
Examples: A book resting on a table, a car cruising at a constant speed on a straight road.
4. Examples and Applications:
Balancing Forces:
Example: A beam balanced on a fulcrum (seesaw) with different weights at different distances from the fulcrum.
Application: Ensuring that the sum of clockwise torques equals the sum of counterclockwise torques for the beam to remain in rotational equilibrium.
Le Chatelier's Principle (Chemical Equilibrium):
Definition: When a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, the system shifts its equilibrium position to counteract the disturbance.
Example: Adding more reactants to a reaction mixture at equilibrium will shift the equilibrium position to produce more products.
Conclusion:
Understanding equilibrium in physical processes is essential for analyzing and predicting the behaviour of systems in various states. By mastering the concepts of static and dynamic equilibrium, translational and rotational equilibrium, and specific examples like thermal and chemical equilibrium, students can build a strong foundation for more advanced studies in physics and chemistry.