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Physical Properties of Matter
Physical Properties of Solids
1. Definite Shape: solids can maintain a definite shape without a container. Crystalline solids have a
definite natural shape: amorphous solids - glass, plastic, etc. have no natural shape (particles arranged
randomly). Crystalline solids generally do not flow because their particles are held in fixed positions.
2. Definite Volume: solids have a definite volume which changes only slightly with temperature or
pressure; very little empty space for compression;
3. Nonfluid: generally crystalline solids do not flow. Amorphous solids also do not flow although in some
cases (i.e.: glass), they can flow at a very slow rate over time.
4. Definite Melting Point : the melting point is the temperature at which a solid becomes a liquid. At this
point (temperature), the kinetic energy of the particles can overcome the inter-molecular forces
between them and the solid turns into a liquid. Amorphous solids (supercooled liquids) have no
definite melting point and can retain liquid properties even at temperatures at which they appear to be
solid. Because they have no natural shape and no distinct melting point, amorphous solids are not
considered true solids (example; glass, plastics).
5. High Density: most substances are most dense in the solid state because the particles are more closely
packed together (water being an exception). Solid H2 is the least dense solid with a density about 1/320
(.003) of the densest element osmium.
6. Incompressibility: solids are less compressible than liquids or gases. Some may seem compressible
(wood, cork) but are not; their pores are filled with air and the pores are compressed not the wood or the
cork.
7. Very Slow Rate of Diffusion: millions of times slower in solids than liquids. A small amount of
diffusion can be found in some solids; i.e. Zn and Cu plates clamped together for several months.
Physical Properties of Liquids
1. Definite Volume: liquids have a definite volume which changes only slightly with temperature vs. a gas
which expands indefinitely unless enclosed.
2. Fluid: like gases but unlike solids, liquids can flow, i.e.: particles are not bound together in fixed
positions but can move about constantly. This explains why liquids and gases are referred to as fluids.
3. Relative High Density: at normal pressures most liquids are thousands of times as dense as their gas and
only slightly (10%) less dense than their solids.
4. Relative Incompressibility: because liquid particles are more closely packed together they are less
compressible. When water at 20oC is compressed by 1000 atm., its volume is reduced by only 4%
versus a gas whose volume would be .001 as much (1000 times less).
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5. Dissolving Ability: liquids are the most common dissolving agents and among these water is most
useful (considered a universal solvent, i.e. can dissolve many substances due to its polarity).
6. Ability to Diffuse: any liquid (like gases) will gradually diffuse throughout any other liquid in which it
can be dissolved. Diffusion is much slower in liquids than gases because particles are closer together
and impede movement. Diffusion increases at higher temperatures.
7. Surface Tension: Surface tension, a property common to all liquids, is a force that tends to pull adjacent
parts of a liquid surface together, therefore making the surface less penetrable by solid bodies.
a) Capillary Action: the rising of a liquid in a narrow tube due to the attraction between the surface
of the liquid and the surface of the solid.
b) Adhesion: the molecular attraction exerted between different molecules in contact with each
other.
c) Cohesion: Molecular attraction between identical molecules in a liquid.
8. Tendency to Evaporate or Boil:
a) Vaporization - the process by which a solid or liquid changes to a gas.
1. Boiling – a form of vaporization in which the liquid particles change into a gas
throughout the entire liquid.
2. Evaporation - a form of vaporization by which particles escape from the surface of a
non-boiling liquid and enter the gaseous state. Occurs only on the
surface of the liquid but at any temperature.
b) Normal Boiling Point - the temperature at which a liquid boils at one atmosphere (760 mm Hg)
of pressure.
c) Sublimation - process by which a solid turns directly to a gas without passing through the liquid
state.
d) Deposition – process by which a gas turns directly into a solid without passing through the
liquid state.
e) Specific heats (Cp): the amount of heat, in joules (J) or calories (cal), required to raise the
temperature of one gram of a substance one degree centigrade.
Cp ice = 2.1 J/goC
Cp water = 4.2 J/goC
Cp water vapor = 1.87 J/goC
f) Heat of vaporization (Hv) and Heat of Condensation (Hc) - the amount of heat required to
vaporize or condense one gram of a liquid at its boiling point;
Hv for water = 2.3 x 103 J/g. (This is the same for Hc)
g) Heat of fusion (Hf) and Heat of Crystallization (Hcr)- the amount of heat required to melt or
freeze one gram of solid at its melting point:
Hf for ice = 3.4 x 102 J/g (This is the same for Hcr)
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9. Tendency to Solidify: as a liquid is "cooled" its average KE decreases and becomes low enough for
attractive forces to hold the particles together in an orderly arrangement. The substance is now a
solid and this process is called freezing.
Physical Properties of Gases
1.
Gases Have Mass: Hydrogen is the lightest gas at 1 g/mole; radon the heaviest at 222 g/mole.
2.
Gases Expand: gases will expand to fill the entire volume of any container in which the gas is
enclosed. There are no significant attraction or repulsion forces between molecules due to the large
distance between molecules.
3.
Gases Are Compressible: the volume of a gas (unlike solids or liquids) can be easily compressed
(reduced) many times because of the large amount of empty space between molecules.
4.
Gases Are Fluid: gas particles can move past one another very easily because their attractive forces are
negligible. This behavior is similar to liquids; this property is called fluidity and gases and liquids
are said to be “fluids”.
5.
Gases Have Low Densities: density of a gas is about .001 (one thousandth) the density of the same
substance as a liquid or a solid. Water = 18 g/mole = 18cm3 of volume. The volume of one mole
water vapor = 22.4 L = 22,400 cm3. Volume ratio of gas : water is 22,400 : 18 = 1244 : 1
(density of water vapor is therefore .0008 the density of liquid water.)
6.
Gases Exert Pressure: pressure = force per unit area or P = F/A. This pressure is directly proportional
to the temperature of the gas.
7. Gases Diffuse:
a. Diffusion: the movement of one substance through another. Rate of diffusion depends on
particle’s speed, diameter (size), and attractive forces.
b. Effusion: a process by which gas particles under pressure pass through a very small opening
from one container to another. Rates of effusion for different gases are directly proportional to
their particle velocities.
c. Graham’s Law of Diffusion – the rates of diffusion of different gases at the same temperature
and pressure are inversely proportional to the square roots of their molar masses or their
densities.