Gaokao Exam Gaokao Chemistry: Chemical Equilibrium and Reactions 3

Question 1

In oxidation-reduction reactions, the oxidising agent is the species that:

Accepted Answer

Gains electrons and is itself reduced

Answer

An oxidising agent causes oxidation in another species by accepting electrons, and is itself reduced in the process.

Question 2

In the standard hydrogen electrode, the half-reaction is H⁺(aq) + e⁻ → ½H₂(g). The standard reduction potential is defined as:

Accepted Answer

0.00 V by definition

Answer

The standard hydrogen electrode (SHE) is assigned a reduction potential of exactly 0.00 V by convention.

Question 3

The reaction rate of A + B → products is found experimentally to double when [A] doubles (B constant) and quadruple when [B] doubles (A constant). The rate law is:

Accepted Answer

rate = k[A][B]²

Answer

Rate doubles with [A] → first order in A; rate quadruples with [B] → second order in B. Rate = k[A][B]².

Question 4

The activation energy of a reaction can be determined graphically from the slope of a plot of:

Accepted Answer

ln k vs 1/T (Arrhenius plot)

Answer

The Arrhenius equation: ln k = ln A − Ea/(RT); a plot of ln k vs 1/T gives slope = −Ea/R.

Question 5

At 700 K, the equilibrium constant for CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g) is K = 2.0. If [CO] = [H₂O] = 1.0 M and [CO₂] = [H₂] = 0.5 M, the system is:

Accepted Answer

Not at equilibrium; Q < K, reaction goes forward

Answer

Q = (0.5 × 0.5)/(1.0 × 1.0) = 0.25 < K = 2.0, so the reaction proceeds in the forward direction to reach equilibrium.

Gaokao Exam Practice Test

Gaokao Exam Practice Test

Gaokao Exam Gaokao Chemistry: Chemical Equilibrium and Reactions 3