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General Chemistry Principles, Patterns, and Applications, 2011

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quantities or concentrations of the reactants, the stoichiometry of the balanced chemical equation for the<br />

reaction, <strong>and</strong> a tabular format to obtain the final concentrations of all species at equilibrium.<br />

K E Y T A K E A W A Y<br />

<br />

Various methods can be used to solve the two fundamental types of equilibrium<br />

problems: (1) those in which we calculate the concentrations of reactants <strong>and</strong> products<br />

at equilibrium <strong>and</strong> (2) those in which we use the equilibrium constant <strong>and</strong> the initial<br />

concentrations of reactants to determine the composition of the equilibrium mixture.<br />

C O N C E PTUAL P R OBLEMS<br />

1. Describe how to determine the magnitude of the equilibrium constant for a reaction when not all<br />

concentrations of the substances are known.<br />

2. Calculations involving systems with very small or very large equilibrium constants can be dramatically<br />

simplified by making certain assumptions about the concentrations of products <strong>and</strong> reactants. What are<br />

these assumptions when K is (a) very large <strong>and</strong> (b) very small? Illustrate this technique using the<br />

system A + 2B<br />

C for which you are to calculate the concentration of the product at equilibrium<br />

starting with only A <strong>and</strong> B. Under what circumstances should simplifying assumptions not be used?<br />

N U M E R I C A L PR O BL E M S<br />

Please be sure you are familiar with the topics discussed in Essential Skills 7 (Section 15.7 "Essential Skills")<br />

before proceeding to the Numerical Problems.<br />

1. In the equilibrium reaction A + B C, what happens to K if the concentrations of the reactants are<br />

2A B + C?<br />

doubled? tripled? Can the same be said about the equilibrium reaction<br />

2. The following table shows the reported values of the equilibrium PO2 at three temperatures for the<br />

reaction Ag2O s<br />

( ) 2Ag( s) +12O2 g<br />

what you would expect to occur? Why or why not?<br />

( ), for which ΔH° = 31 kJ/mol. Are these data consistent with<br />

T (°C)<br />

PO2 (mmHg) )<br />

150 182<br />

184 143<br />

191 126<br />

3. Starting with pure A, if the total equilibrium pressure is 0.969 atm for the<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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