Copyright The Mc GrawHill Companies Inc Permission required

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. What is HEAT? ? Heat is the sum of the kinetic energies of all the separate particles that make up the body. NOTE: More heat means more internal energy q Heat is energy n The proper unit is JOULE The amount of energy matter contains q can be change by transfer of heat q n 4 -1

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Direction of heat transfer HEAT is transferred FROM a body of HIGH TEMPERATURE TO a body of LOW TEMPERATURE n The INTERNAL ENERGY of the body is altered by the gain or loss of energy during heat transfer q Internal energy: the sum total of all of the energy possessed by the body 4 -2

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Again, HEAT is TRANSFERRED ENERGY n HEAT is the energy transferred between two bodies of different temperature n HEAT FLOWS from the body with HIGH temperature to the body of LOW temperature n Internal Energy is changed by heat transfer 4 -3

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Changing the Temperature of Matter n Some substances are easy to heat (like butter) n Some substances are harder to heat (like water) q q Different materials ALTER THEIR ENERGY AT DIFFERENT ‘RATES’ Different substances have different capacities for storing internal energy We summarize these differences by using the descriptive concept of SPECIFIC HEAT CAPACITY 4 -4

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Specific heat capacity n Formally: Specific heat capacity is the quantity of heat required to change the T of a unit mass by 1 C n Conceptually: Think of specific heat like “thermal inertia”, the “resistance” of a material to changes in its temperature 4 -5

4 -6

Specific heat capacity value depends on: - pressure - temperature - phase of the matter (strong intermolecular forces tend to increase c) 4 -7

Table of Specific Heat Capacities Substance (phase) Specific Heat Capacity J/(Kg K) Aluminum (solid) 900 Brass (solid) 377 Copper (solid) 385 Diamond (solid) 502 Ethanol (liquid) 2460 Gold (solid) 129 Graphite (solid) 720 Iron (solid) 444 Lithium (solid) 3582 Mercury (liquid) 139 Oil (liquid) Water (solid at Oº C) ≈ 2000 4186 2060 4 -8

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Understand specific heat capacity n If we think of specific heat like “thermal inertia”, then n An object who’s temperature is EASILY changed has LOW thermal inertia, and must have LOW specific heat capacity n An object who’s temperature is DIFFICULT to change has LARGE thermal inertia, and must have a LARGE specific heat. 4 -9

4 -10

4 -11

4 -12

4 -13

Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. So far, n n We have characterized materials by the amount of energy they can store, and how easy or difficult it is to change that energy: SPECIFIC HEAT CAPACITY Another way to characterize thermal properties of a material… q HOW WELL (OR POORLY) DOES A MATERIAL ‘CARRY’ ENERGY FROM ONE PLACE TO ANOTHER? 4 -14