Chapter 6 Energy and States of Matter

1
Chapter 6Energy and States of Matter

• Measuring Heat Energy
• Energy and Nutrition

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Heat

• Energy that flows from something warm to
  something cooler
• A hotter substance gives KE to a cooler one
• When heat is transferred (lost or gained), there
  is a change in the energy within the substance

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Learning Check H1

• A. When you touch ice, heat is transferred
• from
• 1) your hand to the ice
• 2) the ice to your hand
• B. When you drink a hot cup of coffee, heat
• is transferred from
• 1) your mouth to the coffee
• 2) the coffee to your mouth

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Solution H1

• A. When you touch ice, heat is transferred
• from
• 1) your hand to the ice
• B. When you drink a hot cup of coffee, heat
• is transferred from
• 2) the coffee to your mouth

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Learning Check H2

• When you heat 200 g of water for 1 minute,
  the water temperature rises from 10C to 18C.
• If you heat 400 g of water at 10C in the same
  pan with the same amount of heat for 1 minute,
  what would you expect the final temperature to
  be?
• 1) 10 C 2) 14C 3) 18C

400 g
200 g
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Solution H2

• 2)14C
• Heating twice the mass of water using the
  same amount of heat will raise the temperature
  only half as much.

400 g
200 g
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Some Equalities for Heat

• Heat is measured in calories or joules
• 1 kcal 1000 cal
• 1 calorie 4.184 J
• 1 kJ 1000 J

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Specific Heat

• Why do some foods stay hot longer than others?
• Why is the beach sand hot, but the water is cool
  on the same hot day?

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Specific Heat

• Different substances have different capacities
  for storing energy
• It may take 20 minutes to heat water to 75C.
  However, the same mass of aluminum might require
  5 minutes and the same amount of copper may take
  only 2 minutes to reach the same temperature.

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Specific Heat Values

• Specific heat is the amount of heat needed to
  raise the temperature of 1 g of a substance by
  1C
• cal/gC J/gC
• water 1.00 4.184
• aluminum 0.217 0.908
• copper 0.091 0.382
• silver 0.057 0.24
• gold 0.031 0.13

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Learning Check H3

• A. A substance with a large specific heat
• 1) heats up quickly 2) heats up slowly
• B. When ocean water cools, the surrounding air
• 1) cools 2) warms 3) stays the same
• C. Sand in the desert is hot in the day, and
  cool
• at night. Sand must have a
• 1) high specific heat 2) low specific heat

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Solution H3

• A. A substance with a large specific heat
• 2) heats up slowly
• B. When ocean water cools, the surrounding air
• 2) warms
• C. Sand in the desert is hot in the day, and
  cool
• at night. Sand must have a
• 2) low specific heat

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Measuring Heat

• Requires
• Grams of substance
• Temperature change ?T
• Specific heat of the substance

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Calculating Heat

• mass x temp. change x specific
  heat
• grams x ?T x Sp. Ht.
  

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Heat Calculations

• A hot-water bottle contains 750 g of water at
  65C. If the water cools to body temperature
  (37C), how many calories of heat could be
  transferred to sore muscles?
• heat g x ?T x Sp. Ht.
  (H2O)
• 750 g x 28C x 1.00
  cal gC
• 21 000

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Learning Check H4

• How many kcal are needed to raise the
  temperature of 120 g of water from 15C to 75C?
• 1) 1.8 kcal
• 2) 7.2 kcal
• 3) 9.0 kcal

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Solution H4

• How many kcal are needed to raise the
  temperature of 120 g of water from 15C to 75C?
• 2) 7.2 kcal
• 120 g x (75C - 15C) x 1.00 cal
• gC

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Energy and Nutrition

• 1 Calorie (nutritional) 1 kcal
• 1 Cal 1000 cal

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Caloric Food Values

• Carbohydrate 4 kcal/g
• Fat 9 kcal/g
• Protein 4 kcal/g

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Foods and Calories

• Food Carbo Fat Protein Energy(kcal
• carrots,
• 1 cup 11 0 1
  50
• banana 26 0 1
  110
• egg 0 6 6
  80
• chicken
• (no skin) 0 3 20
  110
• beef (3 oz) 0 5 22
  130

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Learning Check H5

• 1.0 cup of whole milk contains 12 g of
  carbohydrate, 9.0 g of fat, and 9.0 g of
  protein. How many kcal (Cal) are obtained?
• 1) 48 kcal
• 2) 81 kcal
• 3) 165 kcal

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Solution H5

• 3) 165 kcal
• 12 g carbo x 4 kcal/g 48 kcal
• 9.0 g fat x 9 kcal/g 81 kcal
• 9.0 g protein x 4 kcal/g 36 kcal
• Total kcal 165 kcal