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(a) If \(Q_{c}>K_{c}\), how must the reaction proceed to reach equilibrium? (b) At the start of a certain reaction, only reactants are present; no products have been formed. What is the value of \(Q_{c}\) at this point in the reaction?

Short Answer

Expert verified
(a) If \(Q_c > K_c\), the reaction must proceed in the reverse direction to create more reactants and reach equilibrium. (b) At the start of the reaction, when only reactants are present and no products have been formed, the value of \(Q_c\) is 0.

Step by step solution

01

(a) Understanding the relationship between \(Q_c\) and \(K_c\)

When a reaction is at equilibrium, the concentrations of the reactants and products will stay constant, and the reaction quotient, \(Q_c\), will be equal to the equilibrium constant, \(K_c\). If the reaction is not at equilibrium, the reaction will proceed in a certain direction to reach equilibrium. There are three possible cases: 1. If \(Q_c < K_c\), the reaction has more reactants than products, and it will proceed in the forward direction to create more products and reach equilibrium. 2. If \(Q_c = K_c\), the reaction is at equilibrium, and the concentrations of the reactants and products will stay constant. 3. If \(Q_c > K_c\), the reaction has more products than reactants, and it will proceed in the reverse direction to create more reactants and reach equilibrium. In the given exercise, we are told that \(Q_c\) is greater than \(K_c\), i.e., \(Q_c > K_c\). Therefore, the reaction must proceed in the reverse direction to create more reactants and reach equilibrium.
02

(b) Calculating the value of \(Q_c\) at the start of the reaction

At the start of a reaction, only reactants are present and no products have been formed. Let's denote reactants as 'A' and 'B', and products as 'C' and 'D'. The balanced chemical equation for the reaction can be written as: \(aA + bB \rightleftharpoons cC + dD\) The reaction quotient, \(Q_c\), is calculated as: \(Q_c = \frac{[C]^c[D]^d}{[A]^a[B]^b}\) At the beginning of the reaction, since no products have been formed, the concentrations of 'C' and 'D' are both 0. Therefore, we have: \(Q_c = \frac{0^c \times 0^d}{[A]^a[B]^b} = 0\) Thus, the value of \(Q_c\) at the start of the reaction, when only reactants are present and no products have been formed, is 0.

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Most popular questions from this chapter

For the reaction \(\mathrm{I}_{2}+\mathrm{Br}_{2}(g) \rightleftharpoons 2 \mathrm{IBr}(g), K_{c}=280 \mathrm{at}\) \(150^{\circ} \mathrm{C}\). Suppose that \(0.500 \mathrm{~mol}\) IBr in a 2.00-L flask is allowed to reach equilibrium at \(150^{\circ} \mathrm{C}\). What are the equilibrium concentrations of \(\mathrm{IBr}^{2} \mathrm{I}_{2}\), and \(\mathrm{Br}_{2}\) ?

Write the equilibrium-constant expression for the equilibrium $$ \mathrm{C}(s)+\mathrm{CO}_{2}(g) \rightleftharpoons 2 \mathrm{CO}(g) $$ The table that follows shows the relative mole percentages of \(\mathrm{CO}_{2}(g)\) and \(\mathrm{CO}(g)\) at a total pressure of 1 atm for several temperatures. Calculate the value of \(K_{p}\) at each temperature. Is the reaction exothermic or endothermic?

Which of the following statements are true and which are false? (a) The equilibrium constant can never be a negative number. (b) In reactions that we draw with a single-headed arrow, the equilibrium constant has a value that is very close to zero. (c) As the value of the equilibrium constant increases the speed at which a reaction reaches equilibrium increases.

Consider the equilibrium $$ \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g)+\mathrm{Br}_{2}(g) \rightleftharpoons 2 \operatorname{NOBr}(g) $$ Calculate the equilibrium constant \(K_{p}\) for this reaction, given the following information (at \(298 \mathrm{~K}\) ): $$ \begin{array}{rll} 2 \mathrm{NO}(g)+\mathrm{Br}_{2}(g) & \rightleftharpoons 2 \mathrm{NOBr}(g) & K_{c}=2.0 \\ 2 \mathrm{NO}(g) & \rightleftharpoons \mathrm{N}_{2}(g)+\mathrm{O}_{2}(g) & K_{c}=2.1 \times 10^{30} \end{array} $$

Silver chloride, \(\mathrm{AgCl}(\mathrm{s})\), is an "insoluble" strong electrolyte. (a) Write the equation for the dissolution of \(\mathrm{AgCl}(s)\) in \(\mathrm{H}_{2} \mathrm{O}(l)\). (b) Write the expression for \(K_{c}\) for the reaction in part (a). (c) Based on the thermochemical data in Appendix \(C\) and Le Châtelier's principle, predict whether the solubility of \(\mathrm{AgCl}\) in \(\mathrm{H}_{2} \mathrm{O}\) increases or decreases with increasing temperature. (d) The equilibrium constant for the dissolution of \(\mathrm{AgCl}\) in water is \(1.6 \times 10^{-10}\) at \(25^{\circ} \mathrm{C}\). In addition, \(\mathrm{Ag}^{+}(a q)\) can react with \(\mathrm{Cl}^{-}(a q)\) according to the reaction $$ \mathrm{Ag}^{+}(a q)+2 \mathrm{Cl}^{-}(a q) \rightleftharpoons \mathrm{AgCl}_{2}^{-}(a q) $$ where \(K_{c}=1.8 \times 10^{5}\) at \(25^{\circ} \mathrm{C}\). Although \(\mathrm{AgCl}\) is "not soluble" in water, the complex \(\mathrm{AgCl}_{2}{ }^{\prime}\) is soluble. At \(25^{\circ} \mathrm{C}\), is the solubility of \(\mathrm{AgCl}\) in a \(0.100 \mathrm{M} \mathrm{NaCl}\) solution greater than the solubility of \(\mathrm{AgCl}\) in pure water, due to the formation of soluble \(\mathrm{AgCl}_{2}^{-}\)ions? Or is the \(\mathrm{AgCl}\) solubility in \(0.100 \mathrm{M} \mathrm{NaCl}\) less than in pure water because of a Le Châtelier-type argument? Justify your answer with calculations. (Hint: Any form in which silver is in solution counts as "solubility.")

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