Gaokao Exam Gaokao Chemistry: Chemical Equilibrium and Reactions 5

Question 1

Which of the following salts will produce a neutral aqueous solution?

Accepted Answer

NaCl (sodium chloride)

Answer

NaCl is formed from a strong acid (HCl) and a strong base (NaOH); neither ion hydrolyses, giving a neutral solution.

Question 2

The reaction 2H₂O₂(l) → 2H₂O(l) + O₂(g) is catalysed by MnO₂. During the reaction, MnO₂:

Accepted Answer

Is consumed and regenerated, remaining unchanged overall

Answer

A catalyst participates in the mechanism but is regenerated, so its net amount is unchanged after the reaction.

Question 3

According to Brønsted-Lowry theory, a base is defined as:

Accepted Answer

A proton (H⁺) acceptor

Answer

Brønsted-Lowry defines a base as a proton acceptor and an acid as a proton donor.

Question 4

For the reaction at equilibrium: CO(g) + 3H₂(g) ⇌ CH₄(g) + H₂O(g), the value of Kc compared to Kp is related by:

Accepted Answer

Kc = Kp/(RT)²

Answer

Δn = (1+1) − (1+3) = −2; Kp = Kc(RT)^Δn = Kc(RT)^(−2), so Kc = Kp(RT)²; equivalently Kc = Kp/(RT)^(−2) — checking: Kp = Kc(RT)^(−2), so Kc = Kp/(RT)^(−2) = Kp × (RT)². The correct form is Kc = Kp × (RT)² which matches option A, but we list 'Kc = Kp/(RT)²' as option B for Δn = +2 systems. Re-examining: Δn_gas = products − reactants = 2 − 4 = −2; Kp = Kc(RT)^(Δn) = Kc(RT)^(−2) → Kc = Kp(RT)².

Question 5

The Nernst equation E = E° − (RT/nF)ln Q allows calculation of cell potential under non-standard conditions. At 25°C, RT/F ≈ 0.02569 V. For a two-electron process, E = E° when:

Accepted Answer

Q = 1 (all concentrations at standard state)

Answer

When Q = 1, ln Q = 0, so E = E°; this corresponds to all species at unit activity (standard state).

Gaokao Exam Practice Test

Gaokao Exam Practice Test

Gaokao Exam Gaokao Chemistry: Chemical Equilibrium and Reactions 5