Chapter6

Sailor uc san diego internal energy vs enthalpy

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Unformatted text preview: el J. Sailor, UC San Diego Internal Energy vs Enthalpy Chemical reactions are usually performed in open containers, so it is difficult to measure w, the work performed on the atmosphere. We define the term enthalpy ΔH (the change in (H) to eliminate the need to enthalpy) is separately consider PΔV workthe when calculating internal heat gained or lost energy changes in reactions: when a reaction is ΔH = ΔE + performed atPΔV constant pressure for reactions performed at constant pressure, ΔH = q Chem 6A Michael J. Sailor, UC San Diego Example: endothermic process Water evaporation is an endothermic process. Your body (the surroundings) gets colder when water on it (the system) evaporates. System Surroundings water your body heat (q) ΔH www.ehow.com q > 0 (+) ΔH > 0 (+) Heat flows from the surroundings to the system: an endothermic process Chem 6A Michael J. Sailor, UC San Diego Example: exothermic process Water condensation is an exothermic process. Your body (the surroundings) gets a burn when hot water vapor (the system) condenses on it. www./britishfood.about.com System Surroundings water your body heat (q) q < 0 (-) ΔH ΔH < 0 (-) Heat flows from the system to the surroundings: an exothermic process Chem 6A Michael J. Sailor, UC San Diego www.roadfood.com Chem 6A Michael J. Sailor, UC San Diego Heat Capacity Heat Capacity is the relationship between heat absorbed and temperature change in a substance. Specific heat capacity: quantity of heat required to change the temperature of 1 gram of a substance by 1 K. How much heat does it take to warm up your jacuzzi? www.clearleadinc.com Heat capacity of water: 4.184 J g -1 K-1 1000 of 1000 g 4.184 Volume L jacuzzi: 1000 L J ( 39 $ 20)K ! " " " = 79,500 kJ Initial temperature: 20 °CK L g# Final temperature: 39 °C Chem 6A Michael J. Sailor, UC San Diego Measuring the enthalpy of a reaction: calorimetry The chemical transformation involved in medical hot packs is the dissolution of calcium chloride in water. The enthalpy of so...
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This note was uploaded on 11/16/2011 for the course CHEM 6A taught by Professor Pomeroy during the Spring '08 term at UCSD.

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