Transcript Temp and Kinetic Theory

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
 Celsius
C = 5/9 (F – 32)
F = 9/5C + 32
 Kelvin – scientific scale
K = C + 273.15
O 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 = LoT
 - coefficient of linear expansion which
depends on the material (pg.344)
A = 2AoT
V = 3VoT
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 = VoT
-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)?