Q: For the reaction PbI$$_2(s$$) $$\rightleftharpoons Pb$^{2+}(aq) + 2 I$^-(aq$$), what is the correct $$K_c$$ expression?

$$K_c = [\text{Pb}^{2+}][\text{I}^-]^2$$

Q: Given the reaction: HF(aq) + H$$_2O(l$$) $$\rightleftharpoons H$_3O$^+(aq) + F$^-(aq$$), what is the correct $$K_c$$ expression?

$$K_c = \frac{[\text{H}_3\text{O}^+][\text{F}^-]}{[\text{HF}]}$$

Question 1

Which of the following is the correct equilibrium constant expression ($$K_c) $$for the reaction: CaCO$$_3(s$$) $$\rightleftharpoons$$ CaO(s) + CO$$_2(g$$)?

Accepted Answer

$$K_c = [	ext{CO}_2]$$

Question 2

For the reaction PbI$$_2(s$$) $$\rightleftharpoons Pb$^{2+}(aq) + 2 I$^-(aq$$), what is the correct $$K_c$$ expression?

Accepted Answer

$$K_c = [	ext{Pb}^{2+}][	ext{I}^-]^2$$

Question 3

Why is $$K_p$$ not applicable for the reaction: HF(aq) + H$$_2O(l$$) $$\rightleftharpoons H$_3O$^+(aq) + F$^-(aq$$)?

Accepted Answer

Because there are no gaseous species in the reaction.

Question 4

Given the reaction: HF(aq) + H$$_2O(l$$) $$\rightleftharpoons H$_3O$^+(aq) + F$^-(aq$$), what is the correct $$K_c$$ expression?

Accepted Answer

$$K_c = \frac{[	ext{H}_3	ext{O}^+][	ext{F}^-]}{[	ext{HF}]}$$

Question 5

For the reaction CaCO$$_3(s$$) $$\rightleftharpoons$$ CaO(s) + CO$$_2(g$$), which of the following statements is true?

Accepted Answer

The concentrations of solids are omitted from the equilibrium expression.

Question 6

Which of the following best explains why pure liquids and solids are not included in equilibrium constant expressions?

Accepted Answer

Their concentrations do not change during the reaction.

Question 7

If the equilibrium for PbI$$_2(s$$) $$\rightleftharpoons Pb$^{2+}(aq) + 2 I$^-(aq) is $$disturbed by adding more PbI$$_2(s$$), what will happen to the concentrations of Pb$$^{2+}$$ and I$$^-$$?

Accepted Answer

They will remain unchanged.

Question 8

Which of the following is the correct $$K_p$$ expression for the reaction: CaCO$$_3(s$$) $$\rightleftharpoons$$ CaO(s) + CO$$_2(g$$)?

Accepted Answer

$$K_p = P$$_{	ext{CO}$$_2}$$

Question 9

A student writes the following equilibrium expression for the reaction: PbI$$_2(s$$) $$ightleftharpoons Pb$^{2+}(aq) + 2 I$^-(aq$$): $$K_c = \frac{[	ext{Pb}^{2+}][	ext{I}^-]^2}{[	ext{PbI}_2]}. $$What is wrong with this expression?

Accepted Answer

The concentration of PbI$$_2$$ should not be included because it is a solid.

Question 10

Which of the following reactions would have a $$K_p$$ value?

Accepted Answer

CaCO$$_3(s$$) $$\rightleftharpoons$$ CaO(s) + CO$$_2(g)$$

Writing Equilibrium Constant Expressions for Chemical Equations

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