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Evangelista Torricelli invents the barometer, a device used to measure air pressure in a certain environment. The barometer was important to the gas laws as before the barometer, there was no way to measure atmospheric pressure, which is a key variable in gas behavior. The barometer made pressure a visible and measurable variable.
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Blaise Pascal proved that the atmosphere has weight and that pressure changes with altitude by sending his brother-in-law up a mountain with a barometer. As the altitude increased, the mercury level in the barometer dropped, showing that air pressure decreases with height.
This reinforced the concept that air pressure is not constant—it's measurable and variable. -
Boyle investigates the relationship between the volume of a fixed mass of gas, at constant temperature, and the pressure acting on it. He discovers that pressure is inversely proportional to volume. The Boyle’s Law formula is written as P1V1=P2V2.
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Joseph Black discovered a gas released during chemical reactions like heating magnesium carbonate or limestone (calcium carbonate). He called it "fixed air", which is now known as carbon dioxide (CO₂). Before this, gases were not considered distinct substances.
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Joseph Priestley discovered and isolated oxygen gas by heating mercuric oxide (HgO). Antoine Lavoisier repeated Priestley’s experiments but reinterpreted the results, named the gas “oxygen” and disproved the phlogiston theory. Introduced the idea that chemical reactions involve elements combining in fixed ratios, not mysterious "essences" like phlogiston.
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James Six invents a thermometer that allows maximum and minimum temperatures to be measured over a given time period.
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With the recent development of accurate thermometers, Jacques Charles is able to investigate the relationship between the volume of a gas and its temperature. He does not publish his findings.
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Gay-Lussac publishes Charles’s Law and discovers pressure-temperature relationship. States that the pressure of a gas is directly proportional to its absolute temperature when its volume remains constant—key to thermodynamics and industrial applications.
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Amedeo Avogadro extends on the work of Gay-lussac by proposing that gases consist of very small particles called molecules. His law states that equal volumes of gases under the same conditions of temperature and pressure contain equal numbers of molecules.
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Émile Clapeyron expresses the ideal gas law by combining Boyles, Charles, Gay - lussac's, and Avogadros law into a form known as the ideal gas equation. The modern form of this law states that PV=nRT, where n is the number of moles of gas and R the universal gas constant.
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Johannes van der Waals realises gas laws and kinetic-molecular theory are based on an idealised gas. He develops an equation based on real gas behaviour that takes account of attractive forces between gas particles and the volume occupied by each particle.