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

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.(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 Substance Use Mp(oC) Bp (oC)

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

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

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