UNT CHEM 1415 - Final Exam Study Guide (7 pages)

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Final Exam Study Guide



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Final Exam Study Guide

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Definitions and examples of topics ranging from batteries to redox reactions.


Pages:
7
Type:
Study Guide
School:
University of North Texas
Course:
Chem 1415 - Gen Chem Engineers
Edition:
1
Unformatted text preview:

CHEM 1415 1nd Edition Final Exam Study Guide Lectures 23 27 Lecture 23 November 13 Chemical Equilibrium Concentration Chemical Equilibrium o Dynamic Equilibrium Rates of evaporation or condensation become equal and do not stop at equilibrium and do not go to zero Individual molecules continue to move from the liquid to the vapor phase and back again o The rate of the forward reaction equals the rate of the reverse reaction o Arrows indicate emphasize the dynamic character of the process R P o Reverse reaction Raterev k rev P o Two rates equal at equilibrium Rate for Raterev P k for P eq f R k rev o k rev R eq k The Equilibrium Expression o Using a general chemical reaction aA bB cC dD C c D d o The ratio of concentration is Q A a B b o The expression for the equilibrium constant is always based directly on the reaction stoichiometry o Homogeneous equilibria reactants and products are in the same phase either gaseous or aqueous o Heterogeneous equilibrium multiphase system Equilibrium Concentrations o Strategies to solve equilibrium concentration problems Write a balanced chemical equation for the relevant equilibrium or equilibria Write the corresponding equilibrium expression Create a table of concentrations for all of the reacting species o Example 1 Hydrogen reacts with Iodine gas at elevated temperatures k 59 3 T 400 0 050 M of hydrogen and 0 050 M of Iodine What are the equilibrium concentrations H 2 g I 2 g 2 H I g 2 HI K 59 3 H 2 I 2 H2 HI Initial Concentration 0 050 M 0 050 M 0M Change in Concentration x x 2x Final Concentration 0 050 x 0 050 x 2x 2 I2 K HI H 2 I 2 59 3 2 x 2 59 3 2 0 050 x 2x 7 70 0 050 x 9 70 x 0 39 X 0 040 Therefore H 2 I 2 0 050 0 040 0 010 M HI 2 x 0 080 M Lecture 24 November 18 Equilibrium Concentrations Equilibrium Concentrations o Strategies to solve equilibrium concentration problems Write a balanced chemical equation for the relevant equilibrium or equilibria Write the corresponding equilibrium expression Create a table of concentrations for all of the reacting species o Example 1 Phosphorus trichloride reacts with Chlorine gas to form phosphorus pentachloride at k 33 T 250 0 050 M of PC l 3 and 0 015 M of Cl2 What are the equilibrium concentrations Cl2 g PCl3 g PCl5 g 2 PCl5 K 33 Cl2 PC l3 Cl2 PCl3 PCl5 Initial Concentration 0 015 M 0 050 M 0M Change in Concentration x x x Final Concentration 0 015 x 1 50 x x PCl 5 x 33 59 3 Cl PC l 0 050 x 0 015 x 2 3 K 33 x2 3 145 x 0 025 0 x 0 087 0 0088 Therefore PCl5 x 0 0088 M C l2 0 015 x 0 015 0 0088 006 M PC I 3 0 05 x 0 050 0 0088 0 042 M LeChatelier s Principle o When a system at equilibrium is stressed it responds by reestablishing equilibrium to reduce the applied stress o Effects of a Change in Concentration by considering the reaction quotient Q with the equilibrium constant K Type of Concentration Change Resulting Change in Q Response of System Products increased Q K More reactants formed Products decreased Q K More products formed Reactants increased Q K More products formed Reactants decreased Q K More reactants formed o Effects of a change in Pressure on Equilibrium If number of moles of gases differs between reactants and products a shift in pressure will result in a change in the equilibrium position o Effects of change in temperature on equilibrium Type of Reaction Type of Temperature Change Response of System Exothermic T increase More reactants formed Exothermic T decrease More products formed Endothermic T increase More products formed Endothermic T decrease More reactants formed o Effect of o Effects of a catalyst on Equilibrium Has no effect Lecture 25 November 20 Acids and Bases Bronsted Lowry definition an acid is a proton H donor and a base is a proton acceptor o water can act as both an acid or a base depending on the properties of the other substance o amphoteric refers to any substance that can be either an acid or a base Conjugate acid base pairs o Conjugate acid of a base is the acid formed when the base receives a proton o Conjugate base of an acid is the base formed when the acid gives a proton o pH H 3 O log Example Problem 1 The 5 K a of acetic acidC H 3 COOH is 1 8 10 what is the pH of a 0 10 M solution aq aq C H 3 CO O C H 3 COOH aq H 2 O l H3 O C H 3 COOH aq Initial 0 10 aq H3 O 0 aq C H 3 CO O 0 concentration Change in Concentration x x x Final Concentration 0 10 x X X H 3 O C H 3 CO O K a x 2 1 8 10 5 0 10 1 8 10 6 x 1 3 10 3 M pH log 1 3 10 3 2 9 Free Energy and Chemical Equilibrium o Equilibrium a state of minimum free energy o Free energy decreases as you move toward equilibrium from either direction o Chemical systems tend to move spontaneously toward equilibrium o G G RTlnQ Lecture 26 November 25 Redox Reactions and Galvanic Cells Oxidation Reduction and Half Reactions o Oxidation reduction reactions involving the transfer of electrons redox o Oxidation the loss of electrons from some chemical species o Reduction gain of electrons o Half reactions neither one can occur by itself because oxidation and reduction must take place concurrently Galvanic Cell o Salt bridge contains a strong electrolyte that allows either cations or anions to migrate into the solution where they are needed to maintain neutral charge o Galvanic cell any electrochemical cell in which a spontaneous chemic reaction can be used to generate an electric current o Electrochemistry observation of an electric current in a cell led o Electrodes electrically conducting sites at which either oxidation or reduction take place o Anode where oxidation occurs o Cathode where reduction occurs o Cell notation lists metals and ions involved in the reaction Anode electrolyte of anode electrolyte of cathode cathode o Cell potential electromotive force EMF buildup of charge on the electrodes allows for a potential of electrical work w max qE o Nernst equation RT E E lnQ where F 96 485 J V 1 mol 1 nF Relationship between cell potential and free energy RT lnK G nF E E nF Lecture 27 December 02 Corrosion and Batteries Corrosion o Degradation of metals by chemical reactions with the environment slow combination of oxygen with metals to form oxides o Uniform corrosion most visible forms ie rusting of automobiles o Galvanic corrosion occurs when two different metals contact each other in the presence of …


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