5. Solids/Liquids/Gases States of Matter
chapter 12
Three States or Phases of Matter
Solids maintain their own volumes and shapes.
Liquids maintain their own volumes but take the
shape of their containers.
Gases take both the volumes and shapes of their
containers.
What happens when solids melt or liquids boil?
The average energy of the chemical particles of any
substance depends directly on its temperature. The
higher the temperature of that substance the greater
the energy of its atoms, ions or molecules.
Heating an ice cube or a pot of water increases the
energy of all the H2O molecules within it.
A melting point(mp) is the temperature at which a
solid becomes a liquid. The liquid returns to the solid
state at this same temperature; now called the
freezing point(fp).
A boiling point(bp) is the temperature at which a
liquid becomes a gas, usually at normal atmospheric
pressure. When the gas returns to a liquid, at the
same temperature, it is often called the condensation
point.
Solids keep their shape because the energies of
their particles are much smaller than the forces of
attraction holding these particles close to one
another in a crystal lattice, eg. the attraction of Na +
and Cl in sodium chloride(NaCl).
As the solid is heated the energy of the particles
increases to a point at which the attractive forces are
overcome, the particles move further away from
each other and the solid ‘melts’.
Continuing to heat will further increase the energy of
the particles, which will get farther from each
other(evaporate) and the liquid boils.
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
Gas
Formula
Bp.(oC, 1 atm.)
Water
Ammonia
Chlorine
Methane
Oxygen
Fluorine
Nitrogen
Hydrogen
Helium
H 2O
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
Use
Mp(oC)
Vinegar
Acetic acid
17
Window cleaner
Ammonia
-78
Citrus fruit
Citric acid
153
Solvent
Ethyl acetate
-84
Beer/wine/etc
Ethyl alcohol
-117
Jewelry
Gold
1064
Fuel for BBQs
Propane
-190
Table salt
Sodium chloride
801
Lye
Sodium hydroxide
318
Table sugar
Sucrose
185
Paint remover
Toluene
-95
Substance
Bp (oC)
118
–33
dec.
77
78
3080
-42
1413
1390
dec.
111
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