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Chapt 11

# Chapt 11 - Heat Chapter 11 Heat Heat is energy that is...

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1 Heat Chapter 11 Heat circle6 Heat is energy that is transferred between a system and its environment because of a temperature difference between them. circle6 Q is used to represent the amount of energy transferred by heat between a system and its environment Units of Heat circle6 Kilocalorie (kcal) circle6 A kcal is the amount of energy necessary to raise the temperature of 1 kg of water by 1 o C, from 14.5° C to 15.5° C. circle6 This is the “food calorie” circle6 British Thermal Unit (BTU) circle6 A BTU is the amount of energy necessary to raise the temperature of 1 lb of water by 1 o F, from 63° F to 64° F circle6 1 BTU = 252 cal

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2 Joules Method of Measuring the Mechanical Equivalent of Heat circle6 1 kcal = 4186 J circle6 This is called the Mechanical Equivalent of Heat Specific Heats circle6 The amount of heat (Q) per unit mass required to change the temperature of a substance by 1°C is called the specific heat (c) of that substance circle6 Every substance has a unique specific heat. circle6 Units are: J/(kg·C o ) circle6 Thus, for a temperature change of T we can write Q = m·c· T Heat Flow Q = m·c· T circle6 When the temperature increases, ΔT and ΔQ are positive and energy flows into the system circle6 When the temperature decreases, ΔT and ΔQ are negative and energy flows out of the system
3 Table 11-1 Specific Heats of Various Substances (Solids and Liquids) at 20°C and 1 atm Calorimetry circle6 Isolated system barb4right Q = 0 circle6 But if two parts of an isolated system are at

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