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Thermochemistry Energy Heat Thermochemical Equations Calculating Enthalpy Change Reaction Sponteneity
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The Nature of Energy All chemical reactions and changes in the physical state of substances involve either the release or absorption of heat. Energy – the ability to do work or produce heat. Chemical potential energy – energy stored in a substance because of its composition. Heat – energy in the process of flowing from a warmer object to a cooler object. Law of conservation of energy – in any chemical reaction or physical process, energy can be converted to one form to another, but it is neither created nor destroyed. Thermochemistry – the study of heat changes that occur during chemical reactions and physical changes of state.
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Heat Capacity Calorie – the amount of energy required to raise the temperature of one gram of pure water by one degree Celsius. (1 Calorie(kCal) = 1000 cal) Joule – SI unit of energy and of heat. (1 Joule =.2390 calories; 1 calorie = 4.184 joules) Heat capacity – the amount of heat it takes to change an object’s temperature by exactly 1 0 C.
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Concept Practice These examples should go in your notes as we work them in class! (Pg. 265) #3 #4 #5 #6 #7
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Specific Heat Capacity Specific heat – the amount of heat required to raise the temperature of one gram of that substance by one degree Celsius. Thermal Energy Equation: Q = m C T (examples worked in class) (Pg. 267)
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Assignment Pg. 286, 33 – 38 (due Monday (2/3))
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Exothermic and Endothermic Processes Surroundings – everything outside the system. System – the specific part of the universe on which you focus your attention. – Example: A body is a system, what surrounds the body (environment) is the surroundings. A fire warms you, an air conditioner cools you. Universe – the system and surroundings together. – Endothermic process – process that absorbs heat from the surroundings. – Exothermic process – process that loses heat to the surroundings.
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Calorimetry Calorimeter – device used to measure the amount of heat absorbed or released during chemical reactions or physical processes. Calorimetry – the accurate and precise measurement of the heat change for chemical and physical processes. Enthalpy (H) - the heat content for systems at a constant pressure. – Heat and enthalpy are the same thing. - Q = H
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Thermal Energy Equation Q = m x c x T Q = heat (enthalpy) or( H) (J) m = mass (g) c = specific heat (J/g x 0 C) T = final temp. – initial temp. ( 0 C)
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Example 2 (pg. 271) In-class assignment: – Pg. 268, 10 and 11 – Pg. 271, practice problem 15 Due on Wednesday: – Pg. 287, 39-43
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