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Unformatted text preview: 628 Chapter Thirteen Chemical Equilibrium how is the value of K p for the reversed reaction related to the value of K p for the initial reaction? 5. What are homogeneous equilibria? Heterogeneous equilibria? What is the differ- ence in writing K expressions for homogeneous versus heterogeneous reactions? Summarize which species are included in the K expression and which species are not included. 6. Distinguish between the terms equilibrium constant and reaction quotient. When Q K , what does this say about a reaction? When Q K , what does this say about a reaction? When Q K , what does this say about a reaction? 7. Summarize the steps for solving equilibrium problems (see the beginning of Sec- tion 13.6). In general, when solving an equilibrium problem, you should always set up an ICE table. What is an ICE table? 8. A common type of reaction we will study is that having a very small K value ( K V 1). Solving for equilibrium concentrations in an equilibrium problem usu- ally requires many mathematical operations to be performed. However, the math involved when solving equilibrium problems for reactions having small K values ( K V 1) is simplified. What assumption is made when solving the equilibrium concentrations for reactions with small K values? Whenever assumptions are made, they must be checked for validity. In general, the 5% rule is used to check the validity of assuming x (or 2 x , 3 x , and so on) is very small compared to some num- ber. When x (or 2 x , 3 x , and so on) is less than 5% of the number the assumption was made against, then the assumption is said to be valid. If the 5% rule fails, what do you do to solve for the equilibrium concentrations? 9. What is Le Chteliers principle? Consider the reaction 2NOCl( g ) 2NO( g ) Cl 2 ( g ). If this reaction is at equilibrium, what happens when the following changes occur? a. NOCl( g ) is added. b. NO( g ) is added. c. NOCl( g ) is removed. d. Cl 2 ( g ) is removed. e. The container volume is decreased. For each of these changes, what happens to the value of K for the reaction as equi- librium is reached again? Give an example of a reaction for which the addition or re- moval of one of the reactants or products has no effect on the equilibrium position. In general, how will the equilibrium position of a gas-phase reaction be af- fected if the volume of the reaction vessel changes? Are there reactions that will not have their equilibria shifted by a change in volume? Explain. Why does chang- ing the pressure in a rigid container by adding an inert gas not shift the equilib- rium position for a gas-phase reaction? 10. The only stress (change) that also changes the value of K is a change in temper- ature. For an exothermic reaction, how does the equilibrium position change as temperature increases, and what happens to the value of K ? Answer the same ques- tions for an endothermic reaction. If the value of K increases with a decrease in temperature, is the reaction exothermic or endothermic? Explain.temperature, is the reaction exothermic or endothermic?...
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