Post on 09-Jan-2016
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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)?