Solids, Liquids, and Gases

A.  States of Matter

1.  Depends on its molecular motion as measured by temperature.

2.  The Kinetic Theory of Matter says that all matter is made of moving particles.

3.  The four states (or phases) of matter:

a.  Solid

1)  Definite shape and definite volume

2)  Particles are close together (cannot be compressed)

3)  Particles are only vibrating (why solids have definite shapes)

4)  Crystals are repeating geometric patterns of particles

5)  Amorphous solids’ particles are in no definite pattern

b.  Liquid

1)  Definite volume, but an indefinite shape

2)  Particles are close together (can’t be compressed much)

3)  Particles have more energy and move around each other

c.  Gas

1)  Indefinite shape and indefinite volume

2)  Particles are far from each other (can be compressed)

3)  Particles have a lot of energy and move rapidly

d.  Plasma

1)  Hot, ionized gas particles

2)  Particles are electrically charged

3)  The most common state of matter in the universe

B.  Thermal Expansion

1.  Examples:

a.  Expansion joints in bridges and sidewalks

b.  Power lines hanging lower in summer than winter

c.  Metal ball and ring experiment

d.  Bimetallic strip experiment

2.  Particles heat up and expand from one another

3.  Different materials expand at different rates

C.  Changes in State

1.  Melting – the change from a solid to a liquid

a.  Particles speed up and flow around one another

b.  Not enough energy to break away completely

2.  Freezing – the change from a liquid to a solid

a.  Particles slow down

b.  Attractive forces between particles take over

3.  Vaporization – the change from a liquid to a gas

a.  Boiling – rapid; gas bubbles form throughout

b.  Evaporation – slow; occurs at the surface

4.  Condensation – the change from a gas to a liquid

a.  Particles slow down and lose energy

b.  Attractive forces bring particles close together

D.  Heat and State Changes

1.  Heat of fusion

a.  The amount of energy needed to change a material from the solid state to the liquid state

b.  Water’s heat of fusion is 334 kJ/kg

c.  Temperature does not increase while energy for heat of fusion is added

2.  Heat of vaporization

a.  The amount of energy needed to change a material from the liquid state to the gaseous state

b.  Water’s heat of vaporization is 2260 kJ/kg

c.  There is no temperature change during this time

3.  Evaporation is a cooling process

a.  Particles gain energy (heat) and leave as gas particles

b.  They take heat away, leaving the remaining liquid cooler

E.  The Gas Laws

1.  Boyle’s Law

a.  Relates pressure to volume

b.  If temperature is constant, pressure varies inversely with volume

c.  V(1) P(1) = V(2) P(2)

2.  Charles’ Law

a.  Relates temperature to volume

b.  If pressure is constant, temperature varies directly with volume

c.  V(1) / T(1) = V(2) / T(2)

3.  Gay-Lussac's Law

a.  Relates pressure and temperature

b.  As temperature increases (at a constant volume), pressure increases

c.  Ex.  an aerosol can explodes when heated

4.  Units

a.  We will measure pressure in atm (1 atm is standard pressure)

b.  Temperature is measured in Kelvins (273 K is 0 C)

c.  Volume is measured in liters or mL

F.  Fluids

1.  Gases and liquids are considered fluids

2.  All fluids have buoyancy (an upward force on objects)

3.  If the buoyant force is more than the object’s weight, it floats (visa versa)

4.  Archimedes’s Principle

a.  The buoyant force is equal to the weight of the fluid displaced

b.  Therefore, the weight of a floating object is equal to the weight of the fluid it displaces

5.  Pascal’s Principle

a.  Pressure applied to a fluid is transmitted unchanged through the fluid

b.  F(1) / A(1) = F(2) / A(2)

6.  Bernoulli’s Principle

a.  As the velocity of a fluid increases, its pressure decreases

b.  Curved airplane wings force air to move faster over the top; this creates lower pressure above and lift to raise the wings

c.  Curve balls in baseball

d.  Venturi effect

1)  Fluids flow faster in narrow spaces

2)  A faster flow means lower pressure

3)  Wind between skyscrapers has made windows blow out

4)  Trucks passing cars “pull” the car closer