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 **Can cause extreme frostbite Dry ice pellets in a balloon sublime

High energy molecules ‘escape’ from liquid and evaporate/vaporize. Chemical particles absorb heat and leave the orderly crystal lattice for greater ‘freedom of movement’ in the liquid

Boiling Points (Bp) at 1 Atm pressure Gas Formula Bp.( o C, 1 atm.) Water Ammonia Chlorine Methane Oxygen Fluorine Nitrogen Hydrogen Helium H 2 O NH 3 Cl 2 CH 4 O 2 F 2 N 2 H 2 He

Liquid Nitrogen Boils at -196 o C or = 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 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 Substance Use Mp( o C) Bp ( o C) Acetic acid Ammonia Citric acid Ethyl acetate Ethyl alcohol Gold Propane Sodium chloride Sodium hydroxide Sucrose Toluene Vinegar Window cleaner Citrus fruit Solvent Beer/wine/etc Jewelry Fuel for BBQs Table salt Lye Table sugar Paint remover –33 dec dec. 111

Increase Pressure and Decrease Volume (Boyle’s Law)

The Kelvin or absolute temperature scale (T) begins 273 o below the Celsius zero (-273 o C), at absolute zero. To convert o C to Kelvin, add 273 Kelvin statue In Belfast NI Botanical Gardens Queen’s University

Henry’s Law of Gases 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 C 6 H 12 O 6 +6O 2 ---> 6H 2 O + 6CO 2 + Energy! Text Chapter 12.13

Inhale - Partial pressure of O 2 increases in lungs and forces more O 2 into blood to be taken to tissues. Tissues - partial pressure of O 2 is low thus O 2 will enter the tissue from blood; but pressure of CO 2 is high thus forcing CO 2 into blood to return to lungs. Exhale - partial pressure drops and CO 2 escapes. also: ‘decreased oxygen’ at high altitudes ‘excess gases’ in the blood (the ‘bends’)during deep-ocean diving

The 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 %, Oxygen %, Argon - 0.9%, CO 2 and others ~ 0.1% Exhale: Nitrogen %, Oxygen %, Water - 6.1%, Carbon dioxide - 3.7%

Compare the composition of inhaled vs. Exhaled Air!! 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 ie.opening a can of pop/beer 1. High pressure of CO 2 in sealed container causes extra CO 2 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 CO 2 in the drink also drops, more CO 2 escapes and the drink goes flat! (Henry’s Law) also: bicycle/car tires, balloons, gas line explosions

Demonstrations Chemistry is pHun!!

Dry Ice and Liquid Nitrogen Frozen bananas Contracting and expanding balloons Dry Ice sublimation

Nucleation sites Mentos mints in Diet Coke Rough surface of the mints provides nucleation sites for the CO 2 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 Nitrogen Makes up 78% of air Isolated by liquefaction (using liquid Helium) and fractional distillation of air Boiling point -196 o C or 77K. Melting point -252 o C or 21K

Charles Law of Gases Volume of a given mass of gas is directly proportional to its temperature Balloon shrinking in liquid nitrogen

Dry Ice Is solid Carbon dioxide Does not melt at normal pressures, rather it sublimes to the gaseous form

Carbon Dioxide Volcanoes Mentos mints in Diet Coke Increased nucleation sites for dissolved CO 2 leads to rapid evolution of gas

Making Chocolate Ice Cream 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