chapter_17-Lecture 4

# chapter_17-Lecture 4 - Lecture 4 17-46 Comparing Q and K to...

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Lecture 4 17-46

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Comparing Q and K to Determine Reaction Direction PROBLEM: For the reaction N 2 O 4 (g) 2NO 2 (g), K c = 0.21 at 100 o C. At a point during the reaction, [N 2 O 4 ] = 0.12 M and [NO 2 ] = 0.55 M . the reaction at equilibrium? If not, in which direction is it Is the reaction at equilibrium? If not, in which direction is it progressing? PLAN: Write an expression for Q c , substitute with the values given, and ompare the ith the given SOLUTION: compare the Q c with the given K c . Q c = [NO 2 ] 2 = (0.55) 2 12) = 2.5 > K c = 0.21 [N 2 O 4 ] (0.12) Q c is > K c , therefore the reaction is not at equilibrium and will proceed from right to left, from products to reactants, until Q c = K c . 17-47
Steps in solving equilibrium problems. PRELIMINARY SETTING UP 1.Write the balanced equation. 2.Write the reaction quotient, Q . 3.Convert all of the amounts into the correct units ( M or atm). WORKING ON A REACTION TABLE 4.When reaction direction is not known compare Q with K . 5.Construct a reaction table. Check the sign of x , the change in the quantity. 17-48

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Calculating K c from Concentration Data Reaction Table PROBLEM: In order to study hydrogen halide decomposition, a researcher fills an evacuated 2.00-L flask with 0.200 mol of HI gas and allows the reaction to proceed at 453 o C. 2HI( g ) H 2 ( g ) + I 2 ( g ) t equilibrium [HI] = 0 078 Calculate At equilibrium, [HI] = 0.078 M . Calculate K c ?
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chapter_17-Lecture 4 - Lecture 4 17-46 Comparing Q and K to...

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