12 - Quantities of Heat ! ! Heat is energy that is...

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Quantities of Heat ! Heat is energy that is transferred between two objects because of a difference in their temperatures. ! In chemistry, quantities of energy (and heat) are usually expressed with units of joules (J) or calories (cal). 1 cal = 4.184 J ! Nutritionists use the Calorie (Cal) which is a kilocalorie (kcal), or 1000 cal. 1 Cal = 1000 cal = 1 kcal Figure 6.16 Figure 6.16 Q> One serving of cereal James ate this morning has 190 Calories. What is the energy content in units of joules?
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Specific Heat " When heat is added to a substance, the substance increases in temperature. " Specific heat : The amount of heat required to increase the temperature of 1 gram of a substance by 1 ° C. " Specific heat units: J/(g ° C) or cal/(g ° C) " Amount of heat (q) released or absorbed by a substance: q = mC ! T m = mass C = specific heat ! T = temperature change ( = T f - T i ) Q1> How much heat must be added to 15.0 g of water to increase its temperature from 25.0 to 75.0 ° C? Specific heat of water is 4.184 J/(g ° C). Q2> The specific heat of aluminum is 0.895 J/(g°C). If 156 g of aluminum at 75.0°C is cooled to 25.5°C, how much heat is transferred? What is the sign of q , and what is its meaning?
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If 1 kJ of heat were added to each of the following 50.0-gram substances, which would increase in temperature by the greatest amount? Aluminum: 0.895 J/(g ° C) Copper: 0.377 J/(g ° C) Lead: 0.129 J/(g ° C) Calorimetry " Calorimetry is used to determine the heat change of a system by measuring the heat change of its surroundings. " In this calorimeter, an
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This note was uploaded on 04/03/2011 for the course CHEM 111 taught by Professor Cao during the Fall '07 term at Purdue University-West Lafayette.

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12 - Quantities of Heat ! ! Heat is energy that is...

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