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Bellwork Thursday How much energy is required to heat a penny with a mass of 1.23 g from 15oC until it becomes red hot at 256oC? (The specific heat of copper is J/g°C)
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Unit 10 Ch 17 Part 3
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Calorimetry is the measurement of heat change for chemical and physical processes. heat released by system = heat absorbed by surroundings Calorimeter- insulated device used to measure heat change in a chemical or physical process.
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Coffee Cup Calorimeter
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Another type of calorimeter is a bomb calorimeter
Another type of calorimeter is a bomb calorimeter. In a bomb calorimeter, the heat is measured when a substance is burned. Food Calories can be determined in this way.
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Bomb calorimeter
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Ex. A 25 g sample of a metal at 75
Ex. A 25 g sample of a metal at 75.0oC is placed in a calorimeter containing 45 g of H2O at 23.0oC. The temperature stopped changing at 29.4oC. What is the specific heat of the metal? Find q = mC T for the water Find q = mC T for the metal substitute into q water absorbed = q metal releases Solve
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Ex. A 25 g sample of a metal at 75
Ex. A 25 g sample of a metal at 75.0oC is placed in a calorimeter containing 45 g of H2O at 23.0oC. The temperature stopped changing at 29.4oC. What is the specific heat of the metal? q = mC T Twater = = absorbed 6.4oC Tmetal = = released 45.6oC qwater = 45g(4.18J/goC)6.4oC = J qwater = - qmetal J = 25g(Cmetal)45.6oC Cmetal = 1.1 J/goC
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A 25g sample of a metal at ºC is placed in a calorimeter containing 25g of H2O at 20 ºC. The temperature stopped changing at 29.4 ºC. What is the specific heat of the metal? T water = 29.4 – 20 = absorbed 9.4OC T metal = 29.4 – = released 70.6 Solve q water q water = (25g)(4.18 J/goC)(9.4oC) = J q water = q metal so q metal = 982.3J Solve for C in the q metal equation q = mC T 982.3 J = (25 g)Cmetal ( 70.6oC) = 1765 Cmetal C = = J/goC
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Bellwork Friday A 4.92g piece of metal is heated to 108.0°C and dropped into a calorimeter containing 60.0g of water. The water in the calorimeter is 41.0°C. The metal and water both come to a temperature of 99.0°C. What is the specific heat of the metal?
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Bellwork Monday A 65.0g piece of metal is heated to 78.0°C and dropped into a calorimeter containing 100.0g of water. The water in the calorimeter is 21.0°C. The metal and water both end at a temperature of 59.0°C. What is the specific heat of the metal?
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Enthalpy (H)- the amount of heat in a system at a given temperature Enthalpy change: H = q = m C T
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Exothermic reactions have - H Endothermic reactions have + H
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Thermochemical equations include heat changes
Thermochemical equations include heat changes. Physical states must be included. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) kJ H = kJ (energy is released) exothermic H2O kJ 2H2(g) + O2(g) H = kJ (energy is absorbed) endothermic (energy required)
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EXAMPLE CH4(g) + 2O2(g) CO2 + 2H2O + 890kj
Exothermic – energy is a product Endothermic – energy is a reactant ∆H is also called the heat of reaction
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Exothermic - energy is a product Endothermic - energy is a reactant H is also called the heat of reaction.
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Heat in Changes of State The specific heat capacity of water is 4
Heat in Changes of State The specific heat capacity of water is 4.18 J/goC or 1.00 cal/goC The specific heat ice is 2.0 J/goC and the specific heat of steam is 2.1 J/goC. This value is 0.5 cal/goC.
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Notice that these have the same value, but are for opposite processes.
Molar Heat of Fusion- heat required to melt one mole of a solid (6.01 kJ/mol or 334 J/g for water) Notice that these have the same value, but are for opposite processes. q = mHf Molar Heat of Solidification- heat released as 1 mole of liquid freezes. (6.01 kJ/mol or 334 J/g for water)
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Notice that these have the same value, but are for opposite processes.
Molar Heat of Vaporization-heat required to vaporize 1 mole of a liquid. (40.7 kJ/mol or 2260 J/g for water) Notice that these have the same value, but are for opposite processes. q = mHv Molar Heat of Condensation-heat released as 1 mole of a gas condenses to a liquid. (40.7 kJ/mol or 2260 J/g for water)
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Temperature is constant during a phase change!
To find the energy released in a phase change, use… q = moles or grams x heat of phase change Temperature is constant during a phase change!
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Heat of vaporization and heat of condensation. They are equal amounts!
Heat of fusion and heat of solidification. They are equal amounts!
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Bellwork Wednesday Summary 1st
Determine if the following are endothermic or exothermic. H = kJ/mol H = kJ/mol H = kJ/mol H = kJ/mol
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