Chapter 2) Thermal physics

Solid

State where particles are closely packed, arranged regularly, and vibrate in fixed positions

Liquid

State where particles are close together but irregularly arranged and can move past each other

Gas

State where particles are far apart, randomly arranged, and move freely at high speed

Intermolecular forces

Forces of attraction between particles

Strong intermolecular forces

Forces in solids that hold particles tightly together

Weak intermolecular forces

Forces in gases that allow particles to move freely

Particle separation

Distance between particles (small in solids, large in gases)

Brownian motion

Random movement of particles caused by collisions with smaller, fast-moving particles

Melting

Change from solid to liquid

Boiling

Change from liquid to gas throughout the liquid

Evaporation

Change from liquid to gas at the surface only

Condensation

Change from gas to liquid where particles lose energy and come closer together

Solidification (freezing)

Change from liquid to solid where particles lose energy and become fixed

Melting point

Temperature at which a solid changes into a liquid

Boiling point

Temperature at which a liquid changes into a gas

Melting point of water

0°C

Boiling point of water

100°C

Latent heat

Energy used to change state without changing temperature

Why temperature stays constant during melting/boiling

Energy is used to break intermolecular forces instead of increasing kinetic energy

Temperature

Measure of the average kinetic energy of particles (unit °C or K)

Thermal energy

Total energy of all particles in a substance

Evaporation

Occurs at the surface of a liquid at any temperature and is slow

Boiling

Occurs throughout a liquid at a fixed temperature and is fast

Evaporation causes cooling

Higher energy particles escape, lowering the average energy of the remaining liquid

Factors increasing evaporation rate

Higher temperature, larger surface area, increased airflow (draught)

Gas pressure

Force per unit area caused by particle collisions

Increase temperature increases pressure

Particles move faster and collide more frequently and forcefully

Decrease volume increases pressure

Particles collide more often in a smaller space

Heating a gas at fixed volume

Pressure increases

Thermal expansion

Increase in size of a substance when heated

Solids expand

Slightly because particles vibrate more

Liquids expand

More than solids because particles move further apart

Gases expand

Most because particles spread out widely

Order of expansion

Gas > Liquid > Solid

Thermometer

Device used to measure temperature

Liquid thermometer

Works by expansion of a liquid such as mercury or alcohol

Thermistor

Device whose resistance changes with temperature

Thermocouple

Device that produces a voltage when two different metals are heated

Sensitivity

Ability to detect small changes in temperature

Range

Maximum and minimum temperatures that can be measured

Linearity

Equal temperature changes produce equal scale readings

Conduction

Transfer of heat through a material without movement of the material

Conduction in metals

Energy transferred by free electrons moving through the metal

Conduction in non-metals

Energy transferred by vibrations between particles

Good thermal conductors

Materials that transfer heat quickly (e.g. metals)

Poor thermal conductors (insulators)

Materials that transfer heat slowly (e.g. wood, plastic, air)

Why metals feel colder

They conduct heat away from your hand faster than insulators

Convection

Transfer of heat by movement of fluids (liquids and gases)

Convection current

Circulating movement caused by density differences in a fluid

Why convection occurs

Heated fluid becomes less dense and rises, cooler fluid sinks

Why substances rise and fall

Due to density changes caused by temperature differences

Radiation

Transfer of heat by electromagnetic waves

Infrared radiation

Type of electromagnetic radiation that carries heat energy

Absorption

Taking in radiation

Reflection

Bouncing radiation off a surface

Emission

Giving out radiation

Best absorbers and emitters

Dark, dull surfaces

Best reflectors

Light, shiny surfaces

Infrared radiation travels

In straight lines at the speed of light

Infrared radiation is part of

Electromagnetic spectrum

Thermal conductivity

Measure of how well a material conducts heat

Gases and liquids are poor conductors

Particles are far apart so energy transfer is inefficient

Large particles can be moved by

Smaller, fast-moving particles and air or water molecules

Effect on movement of large particles

They move randomly due to uneven collisions

Physical properties of materials

Characteristics that change with temperature

Use of physical properties

To measure temperature changes