Question

question 20 (1 point)
a _______ is a change in one of the conditions in a system at equilibrium.
○ shift
○ catalyst
○ stress
○ pressure
○ reaction quotient
question 21 (1 point)
use the following information to answer the next question.
hydrogen chloride, hcl(g), is a colourless, hygroscopic gas at room
temperature. it is highly soluble in water and reacts with it to form
hydrochloric acid, hcl(aq). an aqueous solution of hydrogen
chloride reacts with the hydrogen carbonate ion, hco₃⁻(aq) to
produce carbonic acid, h₂co₃(aq) and the chloride ion, cl⁻(aq).
which of the following are conjugate acid base pairs for the reaction above?
○ hcl(aq)/hco₃⁻(aq) and h₂co₃(aq)/cl⁻(aq)
○ hco₃⁻(aq)/cl⁻(aq) and hcl(aq)/h₂co₃(aq)
○ hcl(aq)/cl⁻(aq) and hco₃⁻(aq)/h₂co₃(aq)
○ hcl(aq)/h₂co₃(aq) and hco₃⁻(aq)/cl⁻(aq)
○ hco₃⁻(aq)/h₂o(ℓ) and cl⁻(aq)/hcl(aq)

Explanation:

Question 20

To solve this, we recall Le Chatelier's principle. A "stress" is defined as a change in conditions (like concentration, temperature, pressure) of a system at equilibrium. A "shift" is the system's response, a "catalyst" speeds up reaction without stressing equilibrium, "pressure" is a type of stress (not the general term), and "reaction quotient" is a value related to equilibrium. So the term for a change in equilibrium conditions is "stress".

A conjugate acid - base pair differs by one \(H^+\). For the reaction \(HCl(aq)+HCO_3^-(aq)
ightarrow H_2CO_3(aq)+Cl^-(aq)\):

• \(HCl\) donates \(H^+\) to become \(Cl^-\), so \(HCl(aq)/Cl^-(aq)\) is a pair.
• \(HCO_3^-\) accepts \(H^+\) to become \(H_2CO_3\), so \(HCO_3^-(aq)/H_2CO_3(aq)\) is a pair.

We check the options:

• Option 1: \(HCl(aq)/HCO_3^-(aq)\) are not a pair (different \(H^+\) difference logic), \(H_2CO_3(aq)/Cl^-(aq)\) not a pair. Eliminate.
• Option 2: \(HCO_3^-(aq)/Cl^-(aq)\) not a pair, \(HCl(aq)/H_2CO_3(aq)\) not a pair. Eliminate.
• Option 3: \(HCl(aq)/Cl^-(aq)\) (differs by \(H^+\)) and \(HCO_3^-(aq)/H_2CO_3(aq)\) (differs by \(H^+\)) match.
• Option 4: \(HCl(aq)/H_2CO_3(aq)\) not a pair, \(HCO_3^-(aq)/Cl^-(aq)\) not a pair. Eliminate.
• Option 5: \(HCO_3^-(aq)/H_2O\) and \(Cl^-(aq)/HCl(aq)\) do not follow conjugate pair rules. Eliminate.

Answer:

C. stress

Question 21