LecturePLUS Timberlake 991 Chapter 2 Energy and States of Matter Measuring Heat Energy Energy and Nutrition

Energy The capacity to do work (move an object, form a compound, generate light, etc.) LecturePLUS Timberlake 992

Law of Conservation of Energy Total quantity of energy remains constant Energy cannot be created nor destroyed LecturePLUS Timberlake 993

4 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 995 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 996 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

Temperature Measure of the kinetic energy of the random motion of molecules NOT a measure of heat, heat is measured by a CHANGE in temperature LecturePLUS Timberlake 997

Temperature Scales Kelvin and Celsius o C = K – 273 K = o C LecturePLUS Timberlake 998

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Endothermic Energy is absorbed Feels cold Temperature decreases Exothermic Energy is released Feels warm Temperature increases LecturePLUS Timberlake 9910

LecturePLUS Timberlake 9911 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 °C2) 14°C 3) 18°C 200 g 400 g

LecturePLUS Timberlake 9912 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. 200 g 400 g

LecturePLUS Timberlake 9913 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 9914 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 9915 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 9916 Specific Heat Values Specific heat is the a mount of heat needed to raise the temperature of 1 g of a substance by 1°C cal/g°CJ/g°C water aluminum copper silver gold

LecturePLUS Timberlake 9917 Learning Check H3 A. A substance with a large specific heat 1) heats up quickly2) heats up slowly B. When ocean water cools, the surrounding air 1) cools 2) warms3) 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 9918 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 9919 Measuring Heat Requires Grams of substance Temperature change  T Specific heat of the substance

LecturePLUS Timberlake 9920 Calculating Heat mass x temp. change x specific heat grams x  T x Sp. Ht.

LecturePLUS Timberlake 9921 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. (H 2 O) 750 g x 28°C x 1.00 cal g°C =

LecturePLUS Timberlake 9922 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 9923 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

Does a transfer of heat always have to result in a change in temperature? NO! It can result in a change of state or some other change. LecturePLUS Timberlake 9924

Is a change of state a chemical or physical change? PHYSICAL!!! LecturePLUS Timberlake 9925

Heating Curve of Water LecturePLUS Timberlake

LecturePLUS Timberlake 9927 Energy and Nutrition 1 Calorie (nutritional) = 1 kcal 1 Cal= 1000 cal

LecturePLUS Timberlake 9928 Caloric Food Values Carbohydrate = 4 kcal/g Fat = 9 kcal/g Protein = 4 kcal/g

LecturePLUS Timberlake 9929 Foods and Calories FoodCarboFatProtein Energy(kcal carrots, 1 cup banana egg chicken (no skin) beef (3 oz)

LecturePLUS Timberlake 9930 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 9931 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