Ch 10States of Matter — Class 11 Chemistry, concept-first.

Matter around us exists in three distinct physical forms -- solid, liquid and gas -- and every substance can, in principle, be pushed from one of these states into another simply by adding or removing…

Intermolecular forces are the electrical forces of attraction (and, at very short range, of repulsion) that act between neighbouring molecules of a substance -- they are distinct from the much stronge…

Polar molecules -- those in which bonded atoms differ enough in electronegativity that the shared electrons sit closer to one atom than the other -- carry a permanent separation of positive and negati…

Thermal energy is the kinetic energy that particles of matter possess purely because of their own motion, and it rises directly with temperature -- the hotter a sample, the greater the thermal energy…

The gaseous state has several characteristic physical properties that set it apart from solids and liquids: gases are far less dense (lighter) than solids or liquids of the same substance; they have n…

Four measurable quantities describe the state of any confined gas sample -- its pressure (), volume (), absolute temperature () and amount in moles () -- and the experimentally observed relationships…

Robert Boyle, in 1662, carried out a large number of experiments on different gases and found that, at a fixed temperature, increasing the pressure on a fixed amount of gas reduced its volume, and vic…

J. Charles and Gay-Lussac independently found, from experiment, that for a fixed mass of gas held at constant pressure, its volume rises by exactly of its volume at °C for every one-degree rise in tem…

Gay-Lussac's law relates the pressure and absolute temperature of a fixed mass of gas held at constant volume: at constant volume, the pressure () of a fixed amount of gas is directly proportional to…

In 1811, the Italian scientist Amedeo Avogadro combined Dalton's atomic theory with Gay-Lussac's law of combining volumes to propose what is now called Avogadro's law: equal volumes of any gases, meas…

An ideal gas is defined as one that obeys, strictly and at all pressures and temperatures, all three of Boyle's law, Charles's law and Avogadro's law simultaneously.

The ideal gas equation is obtained by combining the three proportionalities of Boyle's, Charles's and Avogadro's laws.

The numerical value of depends entirely on which units are chosen for , and , and is worked out from STP conditions.

Because the number of moles of a known mass of gas is (mass divided by molar mass), substituting this into the rearranged ideal gas equation gives , which rearranges to .

Rearranging the ideal gas equation gives , and since and are both constant for a fixed amount of a particular gas, itself must be constant.

The ideal gas equation can also be recast in terms of a gas's density. Starting from and rearranging to , then substituting gives . Since is the density , this becomes , or equivalently .

John Dalton, alongside his atomic theory, formulated the law of partial pressures in 1801 for mixtures of gases that do not react chemically with one another.

The kinetic molecular theory of gases is a theoretical model that explains WHY gases behave the way the gas laws describe, purely in terms of the motion of their particles.

An ideal gas is one that exactly obeys the ideal gas equation at every temperature and pressure; rearranging to , one mole of a perfectly ideal gas should give at any pressure.

Most gases behave close to ideally at high temperature -- for instance, carbon dioxide's pressure-volume curve at °C closely follows the ideal Boyle's-law curve.

The liquid state sits between the solid and gaseous states: liquid molecules are held together by intermolecular forces that are moderately strong -- strong enough to give a liquid a definite, fixed v…

Molecules at the surface of a liquid constantly have enough energy to escape into the space above the liquid as vapour, a process called evaporation.

Surface tension arises because molecules deep within the bulk of a liquid are pulled equally in every direction by their neighbours, so the net force on them is zero, whereas molecules right at the li…

Viscosity measures the internal friction within a flowing liquid -- how strongly its layers resist sliding past one another.