Gaokao Chemistry: Chemical Equilibrium and Reactions Flashcards

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

Answer: Gains electrons and is itself reduced

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

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

Answer: 0.00 V by definition

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

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:

Answer: rate = k[A][B]²

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

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

Answer: ln k vs 1/T (Arrhenius plot)

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

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:

Answer: Not at equilibrium; Q < K, reaction goes forward

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.

A galvanic cell uses the half-reactions: Zn²⁺/Zn (E° = −0.76 V) and Cu²⁺/Cu (E° = +0.34 V). The standard cell potential is:

Answer: 1.10 V

E°cell = E°cathode − E°anode = 0.34 − (−0.76) = 1.10 V.

The relationship between Gibbs free energy change ΔG° and the equilibrium constant K at temperature T is:

Answer: ΔG° = −RT ln K

The standard thermodynamic relationship is ΔG° = −RT ln K; negative ΔG° means K > 1 (products favoured).