FA16_Lesson16_Calorimetry_ThermoRxns_Hes thermo.pdf

FA16_Lesson16_Calorimetry_ThermoRxns_Hes thermo.pdf - In...

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H−H + H−H + O=O + 3 bonds 4 bonds O H H O H H H−H + H−H + O=O + O H H O H H Energy out of system energy In Lesson 1 we learned about electrostatic potential energy: the potential energy associated with the electrons in atoms and molecules 1 Chem 110: Lesson 16 Our new focus: Chemical energy: the Potential Energy associated with bonding Lesson 16: Thermochemistry is the study of energy changes in chemical processes 2 H 2 (g) + O 2 (g) → 2 H 2 O (g) ΔH rxn = – 483.6 kJ
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2 Chem 110: Lesson 16 Thermochemistry: Pre-Requisite Knowledge Intro to energy (Lesson 1, Units 4-5) Kinetic: energy of motion Potential: stored energy Internal energy E: The capacity to do work or transfer heat ΔE = q + w w = −PΔV work associated with a system at constant P Enthalpy ΔH: heat transferred at constant pressure First Law of Thermodynamics: conservation of energy All energy lost by the system must be gained by the surroundings Energy into system: (+) Energy out of system: (−) Heat out of the system = exothermic (−) Heat into system = endothermic(+) A State Function is a function whose value does not depend on the pathway used to get to the present state Calorimetry: Lesson 13 Unit 2 measure of heat transferred q = C s m ΔT within single phase; q= nΔH for phase transitions
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Examples of chemical changes: Reaction to change chemical composition H rxn (heat of reaction) Formation of a compound from elements H f (heat of formation) 3 Chem 110: Lesson 16 Enthalpy is heat transferred at constant pressure physical changes we’ve seen before… freezing & melting Heat ice at 0 º C and it melts temperature does not change during melting vaporizing & condensing Heat water at 100 º C and it vaporizes temperature does not change during vaporization
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4 Chem 110: Lesson 16 A thermochemical equation is a balanced chemical equation that also includes the enthalpy change . H = H (products) – H (reactants) = H rxn H rxn < 0: ______thermic reaction H rxn > 0: ______thermic reaction Characteristics of Enthalpy: 1. Enthalpy is an extensive property. 2. ΔH for a reaction is equal in magnitude and opposite in sign to ΔH for the reverse reaction. 3. ΔH for a reaction depends on the states of reactants and products (gas, liquid, solid).
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Exothermic and Endothermic Reactions 5 Chem 110: Lesson 16
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6 Chem 110: Lesson 16 The Hydrogen Balloon H 2 (g) + ½ O 2 (g) → H 2 O(g) ΔH rxn = – 241.8 kJ How much heat is given off per mole of O 2 consumed in the production of water? How much heat is required to convert 9 g of water vapor into hydrogen and oxygen gas? H 2 (g) + ½ O 2 (g) ΔHº rxn = – 241.8 kJ H 2 O (g) Clicker question
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7 Chem 110: Lesson 16 Demo: Flaming Cotton 2 Na 2 O 2 (s) + 2 H 2 O ( ) 4 NaOH (aq) + O 2 (g) Clicker question: set iClicker frequency to AD When 25.0 g Na 2 O 2 (molar mass = 78.0 g/mol) react with excess water according to the following reaction, 20.2 kJ of heat is given off.
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FA16_Lesson16_Calorimetry_ThermoRxns_Hes thermo.pdf - In...

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