Question

4 - chemical systems and equilibrium (part 1)
question 1 (1 point)
which of the following is true about a system at equilibrium?
reactants = products
only small observable changes
the forward rate of rxn = reverse rate of rxn
the system is not reversible
question 2 (1 point)
which of the following is not an example of a system at equilibrium?
solid iodine in a saturated solution in a sealed erlenmeyer flask
a closed system
a wet towel in a sealed plastic bag
an open bottle of pop

Explanation:

Question 1

To determine the correct statement about a system at equilibrium, we analyze each option:

• Option 1: \([\text{reactants}] = [\text{products}]\) is incorrect. At equilibrium, the concentrations of reactants and products are constant but not necessarily equal. The equilibrium position depends on the reaction's equilibrium constant (\(K\)).
• Option 2: "Only small observable changes" is incorrect. A system at equilibrium has no net observable changes because the forward and reverse reaction rates are equal, so macroscopic properties (like concentration, pressure, color) remain constant.
• Option 3: "The forward rate of rxn = reverse rate of rxn" is correct. Chemical equilibrium is a dynamic state where the rate of the forward reaction equals the rate of the reverse reaction. This means reactants are converted to products at the same rate as products are converted back to reactants, resulting in no net change in concentrations.
• Option 4: "The system is not reversible" is incorrect. Equilibrium applies to reversible reactions, where both forward and reverse reactions occur. A non - reversible reaction (one that goes to completion) does not reach equilibrium in the same sense.

To identify which is not a system at equilibrium, we recall that a system at equilibrium is a closed system (no matter enters or leaves) where the forward and reverse processes occur at equal rates.

• Option 1: Solid iodine in a saturated solution in a sealed Erlenmeyer flask is at equilibrium. The dissolution of solid iodine (\(\text{I}_2(s)

ightleftharpoons\text{I}_2(aq)\)) and the crystallization of dissolved iodine occur at equal rates in the sealed (closed) flask.

• Option 2: A closed system is a prerequisite for equilibrium (in the context of chemical/physical equilibrium involving matter transfer). A closed system can be at equilibrium if the forward and reverse processes are balanced.
• Option 3: A wet towel in a sealed plastic bag is at equilibrium. The evaporation of water from the towel and the condensation of water vapor back onto the towel occur at equal rates in the sealed (closed) bag.
• Option 4: An open bottle of pop is not at equilibrium. In an open bottle, the carbon dioxide gas (\(\text{CO}_2\)) dissolved in the pop can escape to the atmosphere (the system is open, matter is leaving). The reverse process (dissolution of \(\text{CO}_2\) from the atmosphere back into the pop) is negligible compared to the escape, so the forward process (escape of \(\text{CO}_2\)) is not balanced by the reverse process.

Answer:

The forward rate of rxn = reverse rate of rxn

Question 2