Temperature and Kinetic Theory. Atomic Theory Atom – smallest piece of mater Atomic Mass unit...

Temperature and Kinetic Theory

Atomic Theory

Atom – smallest piece of mater Atomic Mass

unit – atomic mass unit – amu

1amu = 1.66 x 10-27 kg Molecular Mass - sum of all masses in molecules Brownian motion – atoms are in continuous

motion

Examples

What is the atomic mass of He in amu? What is this mass in kg?

What is the molecular mass of Fe2O3 in amu? What is this mass in kg?

Properties

Atoms and molecules exert attractive and repulsive forces on each other

Solids – attractive forces are strong enough to hold the particles in fixed positions

Liquids – move faster, forces are weaker, particles roll over one another

Gases – forces very weak, particles do not stay together

Temperature

Measure of average kinetic energy (speed) – higher temperature means particles are on average moving faster

Many properties change with temperature: size, electrical resistance, color of light emitted

Thermometer – instrument that measures temperature (relies on expansion of materials)

Temperature Scale

CelsiusC = 5/9 (F – 32)F = 9/5C + 32

Kelvin – scientific scaleK = C + 273.15O K – absolute zero – all atomic motion stops

Thermal Equilbrium

When two objects of different temperature are placed in contact, they will eventually reach the same temperature

Heat flows from high temp. to low temp. Zeroth Law of Thermodynamics – if two

systems are in thermal equilibrium with a third system, then they are in thermal equilibrium with each other

Thermal Expansion

Expansion of a material due to an increase in temperature

Amount a substance expands or contracts depends on the material

The amount the length changes is directly proportional to the amount the temp changes and the original length

Expansion Equations - Solids

L = LoT - coefficient of linear expansion which

depends on the material (pg.344)

A = 2AoT

V = 3VoT

Example

A steel bed of a suspension bridge is 200m long at 20°C. If the extreme temperatures are -30°C and 40°C, how much will it contract or expand?

Example

An iron ring is to fit snug on a cylindrical iron rod. At 20°C, the diameter of the rod is 6.445cm and diameter of the ring is 6.420cm. To slip over, the ring must be slightly larger than the rod by about .008cm. To what temperature must the ring be heated?

Volume Expansion - Liquid

Volume change of the liquid can be related by a similar equation

V = VoT

-coefficient of volume expansion

Example

A 70L steel gas tank is filled at 20°C. The car is left to sit in the sun and the tank reaches 40°C. How much gas would overflow from the tank (if any)?