Equilibrium

Introduction

Equilibrium is a central concept in physics and chemistry, referring to the state of a system in which all competing influences are balanced. In a state of equilibrium, a system experiences no net change and appears to be static. However, this does not mean that nothing is happening, just that the various forces or changes balance each other out.

Types of Equilibrium

Static Equilibrium

A system is in static equilibrium when it is at rest, or its center of mass moves at constant velocity. This means that the net force and net torque on every part of the system is zero. For example, a book lying on a table is in static equilibrium.

Dynamic Equilibrium

A system is in dynamic equilibrium when it is in motion with constant velocity. This means that, while there may be movements or processes happening within the system, the overall state of the system does not change over time because the rate of forward process equals the rate of the reverse process.

Mechanical Equilibrium

Mechanical equilibrium is a situation where forces are balanced. It is a type of static equilibrium. The sum of forces, as well as the sum of the torques, on an object is zero. For example, a seesaw with two children of equal weight is in mechanical equilibrium. Mathematically, we can express mechanical equilibrium via the following two conditions:

Chemical Equilibrium

In chemistry, a chemical equilibrium is a state in which the rate of the forward reaction equals the rate of the backward reaction. The concentrations of reactants and products remain constant over time in a chemical equilibrium.

The condition for chemical equilibrium for a reaction is given by the law of mass action:

where , , , are the molar concentrations of the reactants and products, , , , are the stoichiometric coefficients, and is the equilibrium constant.

Thermal Equilibrium

Two systems are in thermal equilibrium if they are in contact, no net heat flows between them, and they are at the same temperature. This is the basis for the zeroth law of thermodynamics, which postulates that if two systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other.

Conclusion

Equilibrium is a fundamental concept in various fields of science, including physics, chemistry, and biology. Understanding equilibrium systems is crucial in studying many natural phenomena, as well as in engineering and medical applications.

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