Conductors vs. Insulators Energy and Heat Conductors vs. Insulators Thermal Conductivity Specific Heat

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

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

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

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

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

Thermal Conductivity & Specific Heat Why does the metal of your chair feel so much colder than the wood of the desk? 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

Conductors vs. Insulators Conduct thermal energy very well Heats up and cools down quickly Do not conduct thermal energy very well Heats up and cools down slowly LecturePLUS Timberlake 99

Thermal Conductivity & Specific Heat Why does the metal of the seat buckle burn your hand but the cloth does not? (Hint: They are the same temperature!) The metal is a conductor that has a higher thermal conductivity and therefore transfers the heat to your hand very quickly burning your hand! LecturePLUS Timberlake 99

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

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. (how easily it changes temp when losing or gaining energy) Look at theTable . The specific heat of the cloth of a seat belt is more than twice that of the metal buckle. So, for equal masses of metal and cloth, the same thermal energy will increase the temperature of the metal twice as much as the cloth. The higher the specific heat of something is, the more energy it takes to increase its temperature. Table 2 shows that most metals have very low specific heats. On the other hand, the specific heat of water is very high. This is why swimming-pool water usually feels cool, even on a hot day. The same energy heats up the air more than it heats up the water. LecturePLUS Timberlake 99

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

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

LecturePLUS Timberlake 99 Measuring Heat (Q) Requires Grams of substance (mass) Temperature change (T) Specific heat of the substance (c) Unlike temperature, energy transferred between objects can not be measured directly. Instead, it must be calculated. When calculating energy transferred between objects, you can use the definition of heat as the amount of energy that is transferred between two objects that are at different temperatures. Heat can then be expressed in joules (J). LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Calculating Heat LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Learning Check H4 A hot-water bottle contains 750 g of water at 65°C. If the water cools to body temperature (37°C), how many joules of heat could be transferred to sore muscles? (SH of water = 4, 184 J/kg*oC) LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Solution H4 A hot-water bottle contains 750 g of water at 65°C. If the water cools to body temperature (37°C), how many joules of heat could be transferred to sore muscles? (SH of water = 4, 184 J/kg*oC) LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Learning Check H5 How many joules of heat are needed to raise the temperature of 120 g of water from 15°C to 75°C? (SH of water = 4, 184 J/kg*oC) LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Solution H5 How many joules of heat are needed to raise the temperature of 120 g of water from 15°C to 75°C? (SH of water = 4, 184 J/kg*oC) LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Learning Check H6 What is the specific heat of lead if 57.0 J are needed to raise the temperature of 35.6 g of lead by 12.5 C? Q c = ----------------- m x t LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Solution H6 What is the specific heat of lead if 57.0 J are needed to raise the temperature of 35.6 g of lead by 12.5 C? Q c = ----------------- m x t LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Learning Check H7 What is the specific heat of sodium if 123 J are needed to raise the temperature of 4.00 g of sodium by 25.0 C? Q c = ----------------- m x t LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Solution H7 What is the specific heat of sodium if 123 J are needed to raise the temperature of 4.00 g of sodium by 25.0 C? Q c = ----------------- m x t LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Learning Check H8 How many joules of heat are absorbed by 45.2 g of aluminum if its temperature rises from 12.5 C to 76.8 C (See Table 3.9)? LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Solution H8 How many joules of heat are absorbed by 45.2 g of aluminum if its temperature rises from 12.5 C to 76.8 C (See Table 3.9)? LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Learning Check H9 Some cooking pans have a layer of copper on the bottom. How many joules are needed to raise the temperature of 125 g of copper from 22 C to 325 C if the specific heat of copper is 0.385 J/g C? LecturePLUS Timberlake 99

LecturePLUS Timberlake 99 Solution H9 Some cooking pans have a layer of copper on the bottom. How many joules are needed to raise the temperature of 125 g of copper from 22 C to 325 C if the specific heat of copper is 0.385 J/g C? LecturePLUS Timberlake 99

Heat and Temperature Heat: Heat is the energy that flows from one object to another when there is a difference in temperature between the objects. Heat is the average kinetic energy of atoms or molecules making up the system. Temperature: Temperature is an indication of whether or not and in which direction, the heat will flow (Temperature is an indication of the average of kinetic energy of atoms or molecules).