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Temperature and Temperature and HeatHeat

•TemperatureTemperature is the measurement of the avg. KE of the molecules in a material.

•HeatHeat is the transfer of KE from one material to another.

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CO N DUCT I O N CO N VECT I O N RA DI A T I O N

T H ERM AL EN ERGY T RA N S FER

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ConductionConduction•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.

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ConvectionConvection•Transfer of thermal Transfer of thermal energy in liquids and energy in liquids and gases.gases.

•Matter actuallyMatter actually movesmoves from one from one place to place to another.another.

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RadiationRadiation•Transfer of Transfer of thermal thermal energy by energy by electromagnetic waveselectromagnetic waves

•Transferring energy Transferring energy through space...through space...NO MATTER NO MATTER IS REQUIRED!IS REQUIRED!

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Exothermic and Endothermic Reactions

• A reaction in which heat is given out is exothermic.

• A reaction in which heat is taken in is endothermic.

https://www.youtube.com/watch?v=mamoT11TEV4https://www.youtube.com/watch?v=cVydmlz0F-Ehttps://www.youtube.com/watch?v=GQkJI-Nq3Os

https://www.youtube.com/watch?v=L-G7pLufXAo

Specific HeatSpecific Heat•Adding Energy to a material

Causes the temperature to go up.

•Taking energy away from a substance causes the temp. to go down!

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•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!

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Water Water absorbsabsorbs a lot a lot of heat energy of heat energy before its before its temperaturetemperature changes while changes while sandsand needs little heat needs little heat energy before its energy before its temperature temperature increases.increases.

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https://www.youtube.com/watch?v=UtyyUHJGsUY

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Examples of Specific Heats

Specific HeatSpecific Heat•The amount of energy required to raise the temperature of a material (substance) by 1°C.

•It takes different amounts of energy to make the same temp. change in different substances.

•We call the amount required: Specific Heat (Cp)!

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Specific Heat of Specific Heat of waterwater

•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).

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Example:Example:Specific Heat of Specific Heat of

WaterWater•Cp = 4,184 Joules of energy to raise the temperature of 1kg 1°C.

• video clipvideo clipWhy Cp?

Cp Stands for “Heat Capacity”

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Calculating Specific Calculating Specific HeatHeat

The Greek letter Δ means “change The Greek letter Δ means “change in”in”

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A hot-water bottle contains 750. g of water at 65.0 °C. If the water cools to body temperature (37.0 °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

SHwater = 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

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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

= 21 000 cal

Sample Calculation for Heat

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Learning CheckHow many kilojoules are needed to raise thetemperature of 325 g of water from 15.0 °C to

77.0 °C?

1) 20.2 kJ

2) 84.3 kJ

3) 105 kJ

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2) 84.3 kJ

STEP 1 Given: 325 g of water warms from 15.0 °C to 77.0 °C

Cwater = 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 3 Write the heat equation:

Heat (joules) = mass (g) x T x SH

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Solution (continued)STEP 4 Substitute given values and solve for

heat:

A copper A copper ornament has a ornament has a

mass of 0.0693 kg mass of 0.0693 kg and changes from and changes from a temperature of a temperature of 20.0°C to 27.4ºC. 20.0°C to 27.4ºC. How much heat How much heat

energy did it gain?energy did it gain?

A 200 JC 540 J

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B 460 JD 740 J

Your Turn!!Show me your work, correct rounding and units!!

1. What is the specific heat of a substance that absorbs 2500. joules of heat when a sample of 100. g of the substance increases in temperature from 10.0 °C to 70.0°C?

2. If 200. grams of water is to be heated from 24.0°C to 100.0°C to make a cup of tea, how much heat must be added? The specific heat of water is 4.184 J/g∙C

3. How many grams of water would require 2200. joules of heat to raise its temperature from 34.0°C to 100.0°C? The specific heat of water is 4.184 J/g∙C

4. A block of aluminum weighing 140. g is cooled from 98.4°C to 62.2°C with the release of 1080. joules of heat. From this data, calculate the specific heat of aluminum.

5. 100.0 g of 4.00°C water is heated until its temperature is 37.0°C. If the specific heat of water is 4.184 J/g°C, calculate the amount of heat energy needed to cause this rise in temperature.