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The Discovery of Gases and Their Ideal Behaviour

The Discovery of Gases and Their Ideal Behaviour. CM2004 States of Matter: Gases . The Discovery of Gases. Gases were the last “State of Matter” to be explored by scientists, even though their description is more straightforward than that of solids or liquids

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The Discovery of Gases and Their Ideal Behaviour

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  1. The Discovery of Gases and Their Ideal Behaviour CM2004 States of Matter: Gases

  2. The Discovery of Gases • Gases were the last “State of Matter” to be explored by scientists, even though their description is more straightforward than that of solids or liquids • That is because to a first approximation we describe gaseous atoms and molecules as “points” with no volumes or forces of attraction/repulsion occurring between them • Their initial discovery and isolation was made in the period 1650-1800.

  3. Johann Baptista van Helmont (ca. 1648) • The first person to state in print that several kinds of gas existed each with different properties • He coined the word GAS (Gk “khaos” for empty space) to describe the product of some chemical reactions e.g charcoal burning

  4. Gas Sylvestre (Gas from Wood) • We know this gas today as CARBON DIOXIDE. • van Helmont’s work indicated that it was produced not only from burning charcoal but also from spa water, fermenting wine and eructions.

  5. “Airs” and Gases • So-called “Fixed Air” was first synthesised by Joseph Black in 1750-1752 by heating magnesium carbonate • He named it so because it was “fixed” (absorbed) by alkalis • It was identical to van Helmont’s, Gas Sylvestre, discovered in 1648

  6. Fire Air • Carl Scheele discovered 'fire air' (an “air” which supported combustion) sometime before 1773.  He produced it by reacting aqua fortis (nitric acid) with potash.  • He showed that “common air” consisted of “fire air” and “foul air”

  7. Pneumatic ChemistryL.pneumaticus "of the wind,belonging to the air" • Joseph Priestley (1733-1804) was an “observational scientist”, who used devices such as the burning lens and pneumatic trough to perform experiments • He collected many pure “airs” over water and mercury by his methods (including “fixed air”, “dephlogisticated air” and “acid air”)

  8. Henry Cavendish and Hydrogen • He perfected the pneumatic technique for collecting gases above water, publishing his techniques and new findings in On Fractious Airs (1766). • He investigated "fixed air" and isolated "inflammable air" (hydrogen) in 1766 and investigated its properties. • He showed that it produced water, upon being burned. • The experiment was repeated by Lavoisier who termed the gas HYDROGEN.

  9. Dephlogisticated Air: 1774 • By heating red oxide of mercury (and red lead) Priestley produced isolated, “dephlogisticated air” • It supported breathing in mice about….”five or six times as good as common air” • It supported burning and was indeed Scheele’s “fire air” • Priestley also showed that it was produced by plants such as mint and thereby discovered photosynthesis • He visited Antoine Lavoisier in Paris to discuss his findings..who then…

  10. The Discovery of Oxygen • In 1789 Lavoisier heated mercuric oxide in a closed system and measured the amount of OXYGEN gas liberated. • He reversed the experiment by heating the mercury formed: it took up exactly the amount of oxygen previously made!

  11. N names • Soon after this time “Common Air” was established to consist partly of Oxygen and partly of Fixed Air • The majority of it did not support life or combustion and was called: • Foul Air (by Scheele) and, later, Noxious or Mephic Air (by Black’s student Daniel Rutherford in 1772) • Azote (by Lavoisier in 1789) • Nitrogène (by the industrial chemist and French government Minister, Jean Antoine Chaptal in 1790) • Stickstoff (i.e. literally “suffocating material” in Germanic nations)

  12. Ideal Behaviour of Gases An Ideal Gas is one which exactly obeys (i) Boyle's Law(pV = constant) (ii)Charles' Law(V/T = constant) They lead to the Ideal Gas Law: pV = nRT Look at your CM1000 notes and explore the web-site http://www.ausetute.com.au/idealgas.html

  13. Universal Gas Constant, R • pV = nRT • Experimentally found that 1mole of an “ideal gas” occupies 22.414L at 1atm pressure and 273.15K. HenceR=0.08206 L atm K-1 mol-1 • Note that the product pV has units Nm=Joules (i.e. m2 kg s-2) and therefore the UGC is often stated as:R= 8.314 J K-1 mol-1

  14. Spot Check on Progress • What volume is needed to store 0.050 moles of helium gas at 310.8kPa and 298K? • What pressure will be exerted by 20.16g hydrogen gas in a 10L cylinder at 30oC? • To what temperature does a 500mL cylinder containing 0.40g helium gas need to be cooled in order for the pressure to be 227.1kPa?

  15. The Gas LawsRichard Townley and Henry Power (1659-1660) • Placed equal volumes of air and mercury in a Torricelli U-tube that was inverted into a dish of mercury • They noted the expansion of the included air at different altitudes on Pendle Hill near Burnley • Demonstrated that 'Mountain Ayr' reduced in volume when carried to the bottom of the hill, while 'Valley Ayr' increased at the top • Concluded that an inversely proportional relationship existed between gas pressure and volume • Wrote to Boyle accordingly

  16. Townley and Power’s Law? (aka Boyle’s Law) • Boyle performed similar experiments in his laboratory and published them in 1662 • Power became an elected member of the newly created Royal Society

  17. Temperature and Pressure • Edme Mariotte added an important provision to Boyle’s PV Law in 1676: the temperature must remain constant • Guillaume Amontons invented a mercury-air thermometer and using it showed (in 1702) that equal drops in temperature produce equal drops in pressure of the air i.e. P1/P2=T1/T2

  18. Amonton’s Law?(aka Charles’ Law; aka Gay-Lussac’s Law) • Amonton’s results can be related to Boyle’s Law to state that: “The volume of a gas is directly proportional to its temperature when pressure is constant.” • Amonton’s experiment of 1702 was repeated much later by Jacques Charles, the French balloonist, in 1787 and much, much later by Joseph Louis Gay-Lussac in 1802. • Ironically, in English speaking nations, the Law is generally named after Charles…. who never published his findings! Charles’ Hydrogen Balloon

  19. No Pressure • In 1848 Lord Kelvin established the value for the “absolute zero” in temperature. (When no pressure is exerted by the gas) • Amontons could not quantify such a prediction because temperature scales did not exist in 1702.

  20. Ideality and Absolute Zero • What happens to an ideal gas at Absolute Zero? (It shrinks to no volume!) • What happens to an ideal gas under infinite pressure? (It is squashed out of existence!) • Generally when a gas is squashed it is transformed into another state (liquid or solid) • So we must consider the real world of NON-IDEAL gases

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