Basic Gas Laws compiled and explained with the help of GIFs

Gases behave in a similar way over a wide variety of conditions because to a good approximation they all have molecules which are widely spaced, and nowadays the equation of state for an ideal gas is derived from kinetic theory. The earlier gas laws are now considered as special cases of the ideal gas equation, with one or more of the variables held constant. Featured here are some gas laws with their respective animations.

Boyle’s Law

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Published in 1662, Boyle’s law states that at constant temperature, the product of an ideal gas's pressure and volume is always constant. A major example of Boyle’s law is filling up of air in a tire. We usually fill a tire up to 30-35 psi which is a measurement of pressure. As you put more and more air into the tire, you are forcing all the gas molecules to get packed together, reducing their volume. As long as the air temperature remains the same, you are experiencing a real life example of Boyle's law as you watch the psi change. Its mathematical representation is as follows:

V1/V2=P2/P1 (at constant temperature)

Where V1 equals the original volume, V2 equals the new volume, P1 the original pressure, and P2 the new pressure.

Charles’s Law

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Presented by Jacques Charles in 1787, this gas law states that if the pressure of a gas remains constant, the volume of the gas will increase as the temperature increases. A helium balloon is a common example which shrinks in cold weather but returns to its normal size in warm climate as according to Charles’ law; a gas takes up more space when it is warm. Mathematical representation of Charles’ law is:

V1/T1 = V2/T2

Where V1 equals the original volume, V2 equals the new volume, T1 equals the original temperature, and T2 equals the new temperature.

Gay-Lussac's Law

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The relationship between temperature and volume, at a constant number of moles and pressure, is called Charles and Gay-Lussac’s Law. They observed that if the pressure is held constant, the volume V is equal to constant times the temperature T. Bullets and cannons are based on these principles: gas super-heated by the burning of gun powder is trapped behind the bullet and expands until the bullet leaves the barrel. Gay-Lussac’s Law is expressed as:

Pi/Ti = Pf/Tf

Where Pi = initial pressure, Ti = initial absolute temperature, Pf = final pressure and Tf = final absolute temperature.

Fick’s Law of Diffusion

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Fick’s law of diffusion postulates that a solute will move from a region of high concentration to a region of low concentration across a concentration gradient. The animation shows the molecular diffusion from a microscopic and macroscopic point of view. Initially, there are solute molecules on the left side of a barrier (purple line) and none on the right. The barrier is removed, and the solute diffuses to fill the whole container. In the top part, a single molecule moves around randomly. In the middle compartment, you see that with more molecules, there is a clear trend where the solute fills the container more and more uniformly. The bottom part comprises of enormous number of solute molecules, randomness becomes undetectable: The solute appears to move smoothly and systematically from high-concentration areas to low-concentration areas. This smooth flow is described by Fick’s laws.

Graham’s Law of Diffusion

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Graham’s law states that the rate at which gas molecules diffuse is inversely proportional to the square root of its density. Since volumes of different gases contain the same number of particle (Avogadro’s Law), the number of moles per liter at a given T and P is constant.  Therefore, the density of a gas is directly proportional to its molar mass. When you open a bottle of perfume, it can very quickly be smelled on the other side of the room. This is because as the scent particles drift out of the bottle, gas molecules in the air collide with the particles and gradually distribute them throughout the air.

Ideal Gas Law

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An ideal gas is defined as one in which all collisions between atoms or molecules are perfectly elastic and in which there are no intermolecular attractive forces. In such a gas, all the internal energy is in the form of kinetic energy and any change in internal energy is accompanied by a change in temperature. The general gas equation is formed by the combination of the three laws, and shows the relationship between the pressure, volume, and temperature for a fixed mass of gas.


23855   16/08/2014

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