thermochemistrythermochemistry chapter 11. heat capacity and specific heat the amount of energy...
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HEAT CAPACITY AND SPECIFIC HEAT
• The amount of energy needed to to increase the temperature of an object exactly 10C is the heat capacity of that object. (J/0C)
• The specific heat capacity or simply specific heat of a substance is the amount of heat/ energy needed to raise the temperature of 1g of the substance 10C. (J/g0C)
Calculating Heat Capacity
• The heat capacity of an object is equal to its specific heat times its mass.
• EX. The heat capacity of a 5 gram piece of pure aluminum is equal to:5g X 0.90J/g0C = 4.50 J/0C
Calculating Specific Heat
• C = __q___ = m X ΔT
= heat(joules or calories)mass(g) X change in temperature (0C)
Sample Problem
• How much heat is required to raise the temperature of 250 g of mercury 52 0C?
The specific heat for mercury is:
0.14 J/g0C
SOLVE for q(heat)
• C = __q___ m X ΔT
• Rearrange the specific heat formula to solve for q.
• q = C x m x ΔT
NOW PLUG AND CHUG…
CALORIMETRY• Calorimetry is the accurate and
precise measurement of heat change for chemical and physical processes.
• In calorimetry, the heat released by the system is equal to to the heat absorbed by its surroundings.
• What law describes this relationship?
Calorimeter
• To measure heat changes accurately and precisely, the process must be carried out in an insulated container.
• The insulated device used to measure the absorption or release of heat in chemical or physical processes is called a calorimeter.
Heat of Reaction
• A heat of reaction is the heat change for the equation exactly as it is written.
• For systems at constant pressure, the heat content is the same as a property called the Enthalpy (H) of the system. (q = ΔH)
Thermochemical Equations
• You can treat heat change in a chemical reaction like any other reactant product in a chemical equation.
• A chemical equation that includes the heat change is referred to as a thermochemical equation.