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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 3

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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. Clip 6

Convection Transfer of thermal energy in liquids and gases.Transfer of thermal energy in liquids and gases. The matter actually moves from one place to another.The matter actually moves from one place to another. clip 7

Radiation Transfer of thermal energy by electromagnetic waves (we’ll discuses these more later)Transfer of thermal energy by electromagnetic waves (we’ll discuses these more later) Transferring energy through space... NO MATTER IS REQUIRED!Transferring energy through space... NO MATTER IS REQUIRED! ClipClipClip 8

Exothermic and Endothermic Reactions A reaction in which heat is given out is exothermic. A reaction in which heat is taken in is endothermic.

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! 10

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

16 Examples of Specific Heats

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! 15

Specific Heat of water The Cp is high because H 2 O 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). 16

Example: Specific Heat of Water Cp = 4,184 Joules of energy to raise the temperature of 1kg 1°C. video clipvideo clipvideo clipvideo clip Why C p ? C p Stands for “Heat Capacity” 17

Calculating Specific Heat The Greek letter Δ means “change in” 18

21 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 1 Given: 750 g of water cools from 65 °C to 37 °C SH water = 1.00 cal/g °C Need: calories of heat transferred STEP 2 Calculate the temperature change  T: 65 °C – 37 °C = 28 °C Sample Calculation for Heat

22 STEP 3 Write the heat equation: Heat (cal) = mass(g) x  T x SH STEP 4 Substitute given values and solve for heat: 750 g x 28 °C x 1.00 cal g °C = cal Sample Calculation for Heat

23 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

24 Solution 2) 84.3 kJ STEP 1 Given: 325 g of water warms from 15.0 °C to 77.0 °C SH water = 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 3 Write the heat equation: Heat (joules) = mass (g) x  T x SH

25 Solution (continued) STEP 4 Substitute given values and solve for heat: 325 g x 62.0 °C x J x 1 kJ g °C 1000 J = 84.3 kJ (2)

A copper ornament has a mass of kg and changes from a temperature of 20.0°C to 27.4ºC. How much heat energy did it gain? A 200 J C 540 J 24 B 460 J D 740 J