Chemistry Study Guide

Chemistry Study Guide - Chemistry Study Guide: Chapters 5 &...

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Chemistry Study Guide: *Heat flow (endothermic vs. exothermic) and Phase Changes Exothermic: heat flows out of the system to surroundings (q<0) o From gas to liquid o From liquid to solid o From gas to solid Endothermic: heat flows into the system from surroundings (q>0) o From solid to liquid o From liquid to gas o Form solid to gas *Phase changes (when it changes phases does heat go in or out? (figure in notes) Change in Internal Energy o Delta E = q + w q = heat w = work delta e = change in systems internal energy Work : work done by the system is energy lost by the system (added to the surroundings), hence the negative sign. o w = (-P) (Delta V) P = pressure Delta V = Change in volume *Enthalpy and the calculations that go with it Change in Internal Energy o Delta E = q + w q = heat w = work delta e = change in systems internal energy Work : work done by the system is energy lost by the system (added to the surroundings), hence the negative sign. o w = (-P) (Delta V) P = pressure Delta V = Change in volume Enthalpy o (H) = E + PV Change in Enthalpy: Energy flows as heat at constant pressure: o (Delta H) = (Delta E) + P (Delta V) o (Delta H) = q p = (Delta E) + P (Delta V) Delta H = enthalpy change (J or kJ) Delta E = change in internal energy (J or kJ) P = pressure (atm) (usually constant) Delta V = volume
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o Since –P (Delta V) = work, then can rewrite equation as Delta H = Delta E – work o Delta E also equals the heat transferred (q) plus the work done (w). Therefore: Delta H = q + w – w = q *Heating curves (interrupt and calculations) 1. First the change of state is melting (solid to liquid). a. Temperature stays the same while a substance melts b. Delta H Fusion 2. The second change of state is boiling (liquid to gas). a. Temperature stays the same while a substance boils b. Delta H Vape 3. Heat is taken up in five stages: 1. The heating of the ice 2. The melting of the ice 3. The heating of the water 4. The vaporization of the water 5. The heating of the steam *Heat capacity (warning: make sure you follow your units! Especially with this question)
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This note was uploaded on 02/01/2012 for the course CHM 141 taught by Professor Sarquis during the Fall '08 term at Miami University.

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Chemistry Study Guide - Chemistry Study Guide: Chapters 5 &...

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