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

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 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 Chemistry L. pneumaticus "of the wind,belonging to the air"
Joseph Priestley ( ) 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

13. Universal Gas Constant, R
pV = nRT
Experimentally found that 1mole of an “ideal gas” occupies L at 1atm pressure and K. Hence R= 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= J K-1 mol-1

14. Spot Check on Progress
What volume is needed to store 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 Laws Richard 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