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 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 • 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 • 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 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 273o 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 • 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 - 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 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!! • 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 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 • 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 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 Nitrogen • 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 • 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 CO2 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