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Chapter 6 Energy and States of Matter. Measuring Heat Energy Energy and Nutrition. Heat. Energy that flows from something warm to something cooler A hotter substance gives KE to a cooler one
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Chapter 6Energy and States of Matter Measuring Heat Energy Energy and Nutrition LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
Learning Check H2 When you heat 200 g of water for 1 minute, the water temperature rises from 10°C to 18°C. If you heat 400 g of water at 10°C 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) 14°C 3) 18°C 400 g 200 g LecturePLUS Timberlake 99
Solution H2 2)14°C Heating twice the mass of water using the same amount of heat will raise the temperature only half as much. 400 g 200 g LecturePLUS Timberlake 99
Some Equalities for Heat Heat is measured in calories or joules • 1 kcal = 1000 cal • 1 calorie = 4.18J • 1 kJ = 1000 J LecturePLUS Timberlake 99
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? LecturePLUS Timberlake 99
Specific Heat Different substances have different capacities for storing energy It may take 20 minutes to heat water to 75°C. 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. LecturePLUS Timberlake 99
Specific Heat Values Specific heat is the amount of heat needed to raise the temperature of 1 g of a substance by 1°C cal/g°C J/g°C water 1.00 4.18 aluminum 0.22 0.90 copper 0.093 0.39 silver 0.057 0.24 gold 0.031 0.13 LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
Measuring Heat Requires • Grams of substance • Temperature change T • Specific heat of the substance LecturePLUS Timberlake 99
Calculating Heat mass x temp. change x specific heat grams x T x Sp. Ht. LecturePLUS Timberlake 99
Heat Calculations 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? heat = g x T x Sp. Ht. (H2O) 750 g x 28°C x 1.00 cal g°C = 21 000 LecturePLUS Timberlake 99
Learning Check H4 How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C? 1) 1.8 kcal 2) 7.2 kcal 3) 9.0 kcal LecturePLUS Timberlake 99
Solution H4 How many kcal are needed to raise the temperature of 120 g of water from 15°C to 75°C? 2) 7.2 kcal 120 g x (75°C - 15°C) x 1.00 cal x 1 kcal g°C 1000 cal LecturePLUS Timberlake 99
Energy and Nutrition 1 Calorie (nutritional) = 1 kcal 1 Cal = 1000 cal LecturePLUS Timberlake 99
Caloric Food Values Carbohydrate = 4 kcal/g Fat = 9 kcal/g Protein = 4 kcal/g LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
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 LecturePLUS Timberlake 99
