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5. Solids/Liquids/Gases - States of Matter chapter 12. Sometimes a solid becomes a gas without first passing through the liquid state. Such a process is called sublimation, eg. ‘dry ice’(CO 2 ) Above -78 o C, sublimes to the gas without melting

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5. Solids/Liquids/Gases - States of Matter

chapter 12


Sometimes a solid becomes a gas without first passing through the liquid state.

Such a process is called sublimation, eg. ‘dry ice’(CO2)

Above -78oC, sublimes to the gas without melting

**Can cause extreme frostbite

Dry ice pellets in a balloon sublime


Chemical particles absorb heat and leave the orderly crystal lattice for greater ‘freedom of movement’ in the liquid

High energy molecules ‘escape’ from liquid and evaporate/vaporize.


Boiling Points (Bp) at 1 Atm pressure lattice for greater ‘freedom of movement’ in the liquid

GasFormulaBp.(oC, 1 atm.)

Water Ammonia Chlorine Methane Oxygen Fluorine Nitrogen Hydrogen Helium

H2O NH3 Cl2 CH4 O2 F2 N2 H2 He

+100 -33 -35 -164 -183 -188 -196 -259 -269


Liquid nitrogen
Liquid Nitrogen lattice for greater ‘freedom of movement’ in the liquid

  • Boils at -196oC or 273-196 = 77K (Kelvin temp scale))

  • Kept as a liquid in a Dewar Flask (highly insulated)

  • Can cause serious burns

  • shrinking balloons and frozen bananas


Charles law
Charles Law lattice for greater ‘freedom of movement’ in the liquid

  • Illustrated by the shrinking balloon

  • The volume of a fixed mass of gas is directly proportional to its temperature on the Kelvin scale (absolute temperature).


Mp & Bp of Some Common Substances lattice for greater ‘freedom of movement’ in the liquid

SubstanceUseMp(oC)Bp (oC)

Vinegar Window cleaner Citrus fruit Solvent Beer/wine/etc Jewelry Fuel for BBQs Table salt Lye Table sugar Paint remover

118 –33 dec. 77 78 3080-42 1413 1390 dec. 111

Acetic acid Ammonia Citric acid Ethyl acetate Ethyl alcohol Gold Propane Sodium chloride Sodium hydroxide Sucrose Toluene

17 -78 153 -84 -117 1064 -190 801 318 185 -95


Increase Pressure and Decrease Volume

(Boyle’s Law)


The Kelvin or absolute temperature scale (T) begins 273 Volume o below the Celsius zero

(-273oC), at absolute zero.

To convert oC to Kelvin, add 273

Kelvin statue

In Belfast NI

Botanical Gardens

Queen’s University


Henry s law of gases
Henry’s Law of Gases Volume

  • Quantity of gas dissolved in a liquid depends directly on the pressure of that gas on the liquid

  • Important in respiration (breathing)

  • Cellular oxidation of glucose

  • C6H12O6 +6O2---> 6H2O + 6CO2 + Energy!

  • Text Chapter 12.13


Inhale Volume - Partial pressure of O2 increases in lungs and forces more O2 into blood to be taken to tissues.

Tissues - partial pressure of O2 is low thus O2 will enter the tissue from blood; but pressure of CO2 is high thus forcing CO2 into blood to return to lungs.

Exhale - partial pressure drops and CO2 escapes.

also: ‘decreased oxygen’ at high altitudes

‘excess gases’ in the blood (the ‘bends’)during deep-ocean diving


The Volume atmospheric pressure at any point on the earth’s surface or above it is the pressure generated by the combined weight of all the atmospheric gases above that point. ( =14.7lb/sq.in.)

Composition of dry air:

Nitrogen - 78.1%, Oxygen - 20.9%,

Argon - 0.9%, CO2 and others ~ 0.1%

Exhale: Nitrogen - 74.9%, Oxygen - 15.3%,

Water - 6.1%, Carbon dioxide - 3.7%


Compare the composition of inhaled vs exhaled air
Compare the composition of inhaled vs. Exhaled Air!! Volume

  • We use up some oxygen and nitrogen

  • We exhale water vapour and carbon dioxide (both “greenhouse” gases)

  • Are we contributing to global warming just by breathing??


Gas Laws in the Real World Volume

ie.opening a can of pop/beer

1. High pressure of CO2 in sealed container causes extra CO2 to dissolve. (Henry’s Law)

2. When cap is removed the pressure drops to atmospheric causing gases to expand and escape. (Boyle’s Law)

3.. With drop in partial pressure above liquid, the solubility of CO2 in the drink also drops, more CO2 escapes and the drink goes flat! (Henry’s Law)

also: bicycle/car tires, balloons, gas line explosions


Demonstrations
Demonstrations Volume

  • Chemistry is pHun!!


Dry ice and liquid nitrogen
Dry Ice and Liquid Nitrogen Volume

  • Frozen bananas

  • Contracting and expanding balloons

  • Dry Ice sublimation


Nucleation sites
Nucleation sites Volume

  • Mentos mints in Diet Coke

  • Rough surface of the mints provides nucleation sites for the CO2 gas-thus rapid release of carbon dioxide from solution

  • Better with Diet Coke than with regular Coke: no corn syrup or sugar to suppress nucleation sites


Liquid nitrogen1
Liquid Nitrogen Volume

  • Makes up 78% of air

  • Isolated by liquefaction (using liquid Helium) and fractional distillation of air

  • Boiling point -196oC or 77K.

  • Melting point -252oC or 21K


Charles law of gases
Charles Law of Gases Volume

  • Volume of a given mass of gas is directly proportional to its temperature

  • Balloon shrinking in liquid nitrogen


Dry ice
Dry Ice Volume

  • Is solid Carbon dioxide

  • Does not melt at normal pressures, rather it sublimes to the gaseous form


Carbon dioxide volcanoes
Carbon Dioxide Volcanoes Volume

  • Mentos mints in Diet Coke

  • Increased nucleation sites for dissolved CO2 leads to rapid evolution of gas


Making chocolate ice cream
Making Chocolate Ice Cream Volume

  • 0.5 L of half and half cream

  • 0.3L of 3% milk

  • Approx. 0.3 cup of sugar

  • Stir in cocoa until it dissolves

  • Add liquid nitrogen and stir


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