I Chapter 5 Thermochemistry A Chemical energy 1 Energy is...

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I. Chapter 5 - Thermochemistry A. Chemical energy 1. Energy is directly linked to chemistry and a key to understanding how chemical reactions proceed 2. All chemical changes are accompanied with a change in energy a) Burning fuel releases energy b) Forming aluminum metal from bauxite requires massive amounts of energy B. Energy 1. Divided into two main categories: work and heat 2. Also divided into potential and kinetic energy a) Potential: due to composition, position, or condition of the object b) Kinetic: due to the motion of the object 3. Energy is always conserved 4. Measured in Joules (J) or in calories (cal a) J = kgm 2 /s 2 b) Cal=4.184 J C. Work energy 1. That which is required to move matter against an opposing force 2. Obtaining work from chemical systems typically involved the production of gas D. Thermal Energy*** 1. Kinetic energy, associated with random motion of molecules 2. The temperature of an object is a quantitated measure of the kinetic energy of the molecules of that object 3. The higher the kinetic energy, the hotter the object 4. No pulse change or chemical reaction when thermal energy of a substance. E. Heat 1. The transfer of thermal energy for a substance 2. Always transferred from the higher KE substance to the lower KE substance. F. Heat Change 1. The change of heat for a substance can be either positive or negative whamw undergoing a chemical or physical change 2. If a substance releases heat, it is exothermic. 3. It if gains heat, it’s endothermic G. Quantifying Heat Transfer 1. There is often a need to determine how much heat will be transferred between substances a) Typically measured as a change in temperature b) However, not all substances change temperature to the same extent H. Heat Capacity ( C ) 1. Ofa substance is the measure of how it’s temperature will change ( delta T) based on the amount of heat change (q) 2. This does not account for mass I. Specific Heat capacity ( c ) 1. c=(q/mdeltaT)
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2. Accounts for the amount of substance that is involved in the heat change 3. Every substance has varying amounts 4. Units: J/g °C (or J/gK) J. Problem 1. Which of the objects below gained the most heat in the indicated temperature change? (answer=d) a) 25.0 g Fe from 10.0 °C to 25.0 °C b) 8.575 g of Fe from 50 °C to 65 °C c) 100.0 g Fe from 85.0 °C to 40 °C
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  • Fall '07
  • Klindeman

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