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thermochemlecturekotz

thermochemlecturekotz - Thermochemistry Thermochemistry...

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1 Thermochemistry Thermochemistry Principles of Reactivity: Energy and Chemical Reactions Energy Potential (mgh) Kinetic (1/2 mv 2 ) Unit = Joule (Nm or kgm 2 /s 2 ) w = Fd Energy can be used to do work 1 calorie = 4.184J 1kcal = 1Cal = 1,000cal Thermochemistry ENERGY is the capacity to do work or transfer heat. HEAT is the form of energy that flows between 2 objects because of their difference in temperature. Other forms of energy — light electrical kinetic and potential chemical potential energy (stored in the bonds of the compound) Conservation of energy Conservation of energy – Energy can be neither created nor destroyed. First Law of Thermodynamics First Law of Thermodynamics – The total energy of the universe is constant. Reactions involve a rearrangement of atoms which coincides with a change in energy. Reactions in which energy is released are “product favored” reactions. Reaction 1 Reaction 2 Internal Energy (U) – Total energy of the system Kinetic (thermal) energy: Translational Rotational Vibrational Potential energy Nuclear forces Electrostatic attractions (Chemical energy) Intramolecular - Bonds between atoms Intermolecular - Attractions between molecules Temperature and Heat - Heat is not the same as temperature - The more thermal energy a substance has, the greater the motion of its atoms and molecules. - The total thermal energy in an object is the sum of the individual energies of all the atoms, molecules, or ions in that object. The thermal energy of a given substance depends not only on temperature but also on the amount of substance. (E.g. Warm bath vs. hot coffee)
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2 System: System: The portion of the universe under study. Surroundings: Everything else besides the system. Interaction: Interaction: Exchange of energy and or matter between the system and its surroundings. Systems: Open system: Exchanges both matter and energy with its surroundings. Closed system: Closed system: Exchanges only energy with its surroundings. Isolated system: Isolated system: Exchanges neither energy nor matter with its surroundings. Thermal Equilibrium Heat transfer occurs when two objects at different temperatures are brought into contact. Heat energy is transferred until the system comes to thermal thermal thermal equilibrium equilibrium equilibrium. Within a system, the heat lost by the hotter object is equal to the heat gained by the cooler object. When heat transfer occurs across the boundary between a system and the surrounding, the directionality of the heat transfer is described as: Exothermic Exothermic: heat is transferred from a system to the surroundings. Endothermic Endothermic: Heat is transferred from the surroundings to the system Movie Specific Heat Capacity and Energy Transfer Specific Heat: The amount of energy required to increase one gram of a substance by 1K (or o C) Compare heat capacity (J/K) with specific heat capacity (J/gK) and molar heat capacity J/mol K) Specific Heat and Energy Transfer Specific Heat Sample Problems: 1. In an experiment it was determined that 59.8J was required to change the temperature of 25.0g of ethylene glycol (a compound
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