UNIT 5: HEAT

What is heat? What is temperature? How are these related to each other?

KINETIC MOLECULAR THEORY All matter consists of tiny particles These particles are in constant motion The amount of motion is proportional to temperature. Increased temperature means increased motion ex water- solid when below zero, liquid when degrees and steam above 100 Solids, liquids and gases differ in the amount that their particles move and how much they interact

KINETIC MOLECULAR THEORY

HEAT Is the thermal energy transferred from one object to another due to differences in temperatures. Measured in Joules (J) Q heat = E thermal where Q heat = amount of heat; E= change in thermal energy

TEMPERATURE Is a measure of the average kinetic energy of the molecules of a substance. Can be measured with a thermometer Measurements of a thermometer: Celsius ( o C)- freezing point is 0 o C and boiling point is 100 o C Kelvin Scale (K)- sets absolute zero (temperature where no motion occurs) as 0 K ( o C). K= o C +273 or o C= K-273

TEMPERATURE CONVERSIONS Convert these temperature from Celsuis to Kelvin 27 o C = 300 K 560 o C = ? K -184 o C = ? K -273 o C = ? K Convert these temperatures from Kelvin to Celsius 110K = -163 o C 22 K = ? o C 402 K= ? o C 323 K = ? o C

THERMAL EXPANSION When matter is heated, the particles move faster and move apart from each other. This causes the volume to increase. We call this expansion. When matter is cooled, the opposite happens and we get contraction.

EVERYDAY EXAMPLES Air pressure Tires have less pressure in the cold temperatures Experiment: two balloons about the same volume- what will happen when one balloon is put outside in the cold

EVERYDAY EXAMPLES Bridges and sidewalks are built in segments. They have spaces called expansion joints between them. The expansion joints allow the concrete and steel to expand without buckling and cracking. The thumping sound you hear when you drive over a bridge in a car or bus is the sound of the tires going over the expansion joints.

EVERYDAY EXAMPLES Thermometers- liquid in a thermometer will expand with increased temperatures making them rise Global warming is causing ocean levels to rise (due to the expansion of the volume of water) threatening cities at sea level

THERMAL EXPANSION Substances vary in the amount of thermal expansion Demo in small groups- ring and ball demo - compound bar

LINEAR EXPANSION- FOR A SOLID Depends on the initial length, temperature change, and the type of materials it is made from Change in length (Δ L) is directly proportional to the change of temperature (Δ T) and the original length (L o ) ΔL= α L o * Δ T Where: L= length in meters (m); α = coefficient of linear expansion; L o = original length (m); Δ T= change in temperature

EXAMPLE A lead rod is 2.5 m long at 20 o C. What is the change in length if it is heated to 100 o C and α = 27 x o C -1.

SOLUTION  L =  Lo  T = 27 x10 -6 o C -1 x 2.5 m x 80.0 o C = m

VOLUME EXPANSION- FOR GASES ΔV= βV o ΔT Where: ΔV- change in volume (m 3 or L) β – coefficient of volume expansion V o – original length (m 3 or L) ΔT- change in temperature Note: β is different for different materials

EXAMPLE 1000 L of gasoline is in a tank at 20 o C. What is the change in volume when the temperature drops to - 20 o C?( β = 950 x o C)

SOLUTION  V=  V 0  T = 950x10 -6o C -1 X 1000L X -40 o C = -38 L

ASSIGNMENT do expansion practice problems- check answers as you go Expansion problems- do #1-8