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1. Moving Thermal Energy. 3. Temperature and Heat. Temperature is the measurement of the avg. KE of the molecules in a material. Heat is the transfer of KE from one material to another. Clip. 4. Heat flows from WARMER to COLDER!. 5. 6. Clip. Conduction.
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1 Moving Thermal Energy
3 Temperature and Heat • Temperatureis the measurement of the avg. KE of the molecules in a material. • Heatis the transfer of KE from one material to another. Clip
4 Heat flows from WARMER to COLDER!
6 Clip Conduction • The transfer of thermal energy in solids. • Materials must be in direct contact with each other! • Ex: Heating of the bottom of a pot on stove.
7 • clip Convection • Transfer of thermal energy in liquids and gases. • The matter actuallymovesfrom one place to another.
8 • Clip Radiation • Transfer of thermal energy by electromagnetic waves(we’ll discuses these more later) • Transferring energy through space...NO MATTER IS REQUIRED!
Exothermic and Endothermic Reactions • A reaction in which heat is given out is exothermic. • A reaction in which heat is taken in is endothermic.
10 Specific Heat • Adding Energy to a material Causes the • Temperature to go up. • Taking energy away from a substance causes the temp. to • Go down!
Have you ever noticed that on a hot summer day the pool is cooler than the hot cement? • OR maybe that the ocean is cooler than the hot sand? • Why? The sun has been beating down on both of them for the same amount of time........... • It takes more thermal energy to raise the temperature of water that it does the cement! 11
Water absorbs a lot of heat energy before its temperature changes while sand needs little heat energy before its temperature increases. 12
15 Specific Heat • The amount of energy required to raise the temperature of a material (substance). • It takes different amts of energy to make the same temp change in different substances. • We call the amt required: Specific Heat!
16 Specific Heat of water • The Cp is high because H2O mols. form strong bonds w/each other. • It takes a lot of energy to break the bonds so that the the molecules can then start to move around faster (HEAT UP).
17 Example:Specific Heat of Water • Cp = 4,184 Joules of energy to raise the temperature of 1kg 1°C. • video clip Why Cp? Cp Stands for “Heat Capacity”
18 Calculating Specific Heat The Greek letter Δ means “change in”
Sample Calculation for Heat A hot-water bottle contains 750 g of water at 65 °C. If the water cools to body temperature (37 °C), how many calories of heat could be transferred to sore muscles? STEP 1Given: 750 g of water cools from 65 °C to 37 °C SHwater = 1.00 cal/g °C Need: calories of heat transferred STEP 2Calculate the temperature change T: 65 °C – 37 °C = 28 °C
Sample Calculation for Heat STEP 3Write the heat equation: Heat (cal) = mass(g) x T x SH STEP 4Substitute given values and solve for heat: 750 g x 28 °C x 1.00 cal g °C = 21 000 cal
Learning Check How many kilojoules are needed to raise the temperature of 325 g of water from 15.0 °C to 77.0 °C? 1) 20.2 kJ 2) 84.3 kJ 3) 105 kJ
Solution 2) 84.3 kJ STEP 1Given: 325 g of water warms from 15.0 °C to 77.0 °C SHwater = 4.184 J/g °C 1 kJ = 1000 J Need:kilojoules of heat needed STEP 2 Calculate the temperature change T: 77.0 °C – 15.0 °C = 62.0 °C STEP 3Write the heat equation: Heat (joules) = mass (g) x T x SH
Solution (continued) STEP 4Substitute given values and solve for heat: 325 g x 62.0 °C x 4.184 J x 1 kJ g °C 1000 J = 84.3 kJ (2)
A copper ornament has a mass of 0.0693 kg and changes from a temperature of 20.0°C to 27.4ºC. How much heat energy did it gain? A200 J C540 J B460 J D740 J 24
