Ch 8Physical and Chemical Equilibrium — Class 11 Chemistry, concept-first.

Not every change around you runs to completion in one direction. A banana ripening or iron rusting never reverses, but plenty of everyday processes -- even one happening in your own bloodstream right…

Everyday life is full of chemical and physical changes. A banana ripens over a few days, a piece of silver slowly tarnishes, and iron rusts -- and all three of these changes proceed steadily in one di…

Equilibrium is a general idea, not one unique to chemistry. If two people of equal weight sit at equal distances on opposite sides of a see-saw's fulcrum, the see-saw stays level and stationary -- it…

A system is said to be in physical equilibrium when the amount of matter making up each of its different phases stays constant with time, with no perceptible physical change taking place overall.

Physical equilibrium is not limited to a single pure substance changing phase -- it also governs how a solute dissolves into a solvent.

Chemical reactions, much like the physical processes above, gradually settle into a state of equilibrium given enough time. Consider a general reversible reaction

It helps to picture chemical equilibrium through an everyday analogy. Imagine people moving back and forth between the first and second floor of a multi-storey building -- some number of people move u…

Chemical equilibria are further classified according to whether the reactants and products all share a single physical phase or are spread across more than one -- giving homogeneous equilibrium and he…

In a homogeneous equilibrium, every reactant and every product is present in the very same phase. For instance, in

In a heterogeneous equilibrium, the reactants and products of the reaction are spread across more than one phase. The liquid-vapour equilibrium

In 1864, the Norwegian chemists Cato Maximilian Guldberg and Peter Waage formulated the law of mass action, generalising the experimental behaviour of a great many reversible reactions they had studie…

Applying the law of mass action to a general reversible reaction

and describe the very same equilibrium, so they must be related to each other. For the general all-gas reaction , starting from the ideal gas equation , i.e.

For a heterogeneous equilibrium, the equilibrium-constant expression can be simplified further, because a pure solid or pure liquid does not have a variable concentration the way a gas or a dissolved…

Knowing the value of a reaction's equilibrium constant is genuinely useful -- it lets us (1) predict the direction in which the net reaction will proceed from any given starting mixture, (2) predict t…

The numerical value of is itself a direct measure of how far a reaction has proceeded toward product formation at a given temperature.

Knowing tells us where equilibrium lies, but a reaction mixture is not always sitting at equilibrium. To find out which direction a given (non-equilibrium) mixture still needs to move, define the reac…

If the equilibrium concentrations of reactants and products are known, the equilibrium constant can be calculated directly -- and, conversely, if the equilibrium constant is known, the equilibrium com…

Many industrially important chemical reactions -- ammonia synthesis among them -- are reversible, so it matters a great deal to know which reaction conditions will push the equilibrium toward the high…

At equilibrium, the concentrations of reactants and products stay fixed. Adding more of a reactant or a product from outside disturbs this balance by raising that species' concentration -- and, accord…

A change in pressure has a significant effect only on an equilibrium that has gaseous components. Increasing the pressure on the system (which decreases its volume) makes the system respond by shiftin…

If the temperature of a system at equilibrium is changed, the system responds by shifting the equilibrium in whichever direction tends to counteract (absorb) that change in temperature.

Adding a catalyst does not affect the position of a system's equilibrium at all. A catalyst speeds up the forward reaction and the reverse reaction to exactly the same extent, so the equilibrium compo…

An inert gas is one that does not react with any of the species involved in a given equilibrium. Adding such a gas to an equilibrium system held at constant volume raises the total number of moles of…

The Van't Hoff equation gives the precise, quantitative relationship between temperature and the equilibrium constant K.

- In daily life we observe both irreversible changes (a banana ripening, silver tarnishing) and reversible changes; in a reversible reaction, the state at which the rate of the reverse reaction equals…

The textbook's concept map is built around a single title, 'Equilibrium', branching into two broad halves.

This is the textbook's own end-of-chapter evaluation set for the unit, testing the material from the meaning of equilibrium and its physical/chemical classification through the law of mass action, the…

Sample papers and previous-year board questions for this subject.