Equilibrium problems reaction quotient

To use activity coefficients, first solve the equilibrium problem with all activity coefficients equal to unity. From the resulting concentrations, compute the ionic strength and use the Davies equation to find activity coefficients. With activity coefficients, calculate the effective equilibrium constant K for each chemical reaction. K is the equilibrium quotient of concentrations at a particular ionic strength. Solve the problem again with K values and find a new ionic strength. Repeat the cycle until the concentrations reach constant values. 

The correct answer is (B). This is a reaction quotient. Q, problem. You need to calculate Q and then compare it to the equilibrium constant. K. The calculation is as follows ... 

Use the reaction quotient to predict whether a precipitate will form when two solutions are mixed, and then calculate the equilibrium concentrations that result (Section 16.3, Problems 17-24). 

The Reaction Quotient Solving Problems When Not All Equilibrium Concentrations Are Known... 

In spite of the outlined above formulation of chemical equilibrium problem in terms of rigorous thermodynamics (equilibrium constants defined as quotients of activities) which is well known and does not pose any special difficulty when it is compared with formulation in terms of conditional equilibrium constants (defined as quotients of concentrations), the former approach is not very popular, and many equilibrium constants of surface reactions reported in published papers were defined in terms of concentrations. Even praise of use of concentrations rather than activities in modeling of adsorption can be found in recent literature. Many publications do not address this question explicit, and then it is difficult to figure out how the equilibrium constants of surface species were defined K, or Accordingly, the equilibrium constants of surface species reported in tables of Chapter 4 constitute a mixture of constants defined in different ways (K, or The details regarding the definition of equilibrium constants can be found (but not always) in the original publications. 

Skill 9.2 Solving problems involving equilibrium constants and reaction quotients... 

Consider the problem more generally. You are given a reaction mixture that is not yet at equilibrium. You would like to know in what direction the reaction will go as it approaches equilibrium. To answer this, you substitute the concentrations of substances from the mixture into the reaction quotient Q. Then, you compare Qc to the equilibrium constant Kc-... 

Think About K With practice, writing reaction quotients becomes second nature. Without sufficient practice, it will seem inordinately difficult. It is important that you become proficient at this. It is very often the first step in solving equilibrium problems. 

Strategy Using the initial concentrations, calculate the reaction quotient, Q, and compare it to the value of (given in the problem statement of Sample Problem 15.8) to determine which direction the reaction will proceed to establish equihbrium. Then, construct an equilibrium table to determine... 

Figure 8-1 Student data showing that the equilibrium quotient of concentrations for the reaction Fe3 + SCN Fe(SCN)21 decreases as potassium nitrate is added to the solution. Color Plate 3 shows the fading of the red color of Fe(SCN)2 after KN03 has been added. Problem 13-11 gives more information on this chemical system. [From R. J. Stolzberg, "Discovering a Change in Equilibrium Constant with Change in Ionic Strength," J. Chem. Ed. 1999, 76.640.]...

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