Gaokao Chemistry: Chemical Equilibrium and Reactions Flashcards

For the equilibrium N₂(g) + 3H₂(g) ⇌ 2NH₃(g), increasing pressure at constant temperature will:

Answer: Shift the equilibrium toward products (NH₃)

By Le Chatelier's principle, increasing pressure favours the side with fewer moles of gas; the product side has 2 mol vs 4 mol reactants, so equilibrium shifts to products.

The equilibrium constant expression for 2SO₂(g) + O₂(g) ⇌ 2SO₃(g) is:

Answer: K = [SO₃]²/([SO₂]²[O₂])

The equilibrium constant expression uses products over reactants, each raised to the power of the stoichiometric coefficient.

At 25°C, for the reaction H₂(g) + I₂(g) ⇌ 2HI(g), K = 50. If [H₂] = [I₂] = 0.1 M and [HI] = 0.5 M initially, the reaction quotient Q is:

Answer: 25

Q = [HI]²/([H₂][I₂]) = 0.25/(0.1 × 0.1) = 25. Since Q < K, the reaction proceeds forward.

For an endothermic reaction at equilibrium, increasing temperature will:

Answer: Increase K and shift equilibrium toward products

For an endothermic reaction, heat is a 'reactant'; adding heat (increasing T) shifts equilibrium to the product side and increases K.

Adding a catalyst to a reaction at equilibrium:

Answer: Speeds up both forward and reverse reactions equally, leaving equilibrium position unchanged

A catalyst lowers activation energy equally for forward and reverse reactions, reaching equilibrium faster but not changing K or the equilibrium position.

For the reaction A(g) + B(g) ⇌ C(g) + D(g) with K = 4, if [A] = [B] = 1 M and [C] = [D] = x at equilibrium, then x =

Answer: 2 M

K = x²/(1)(1) = 4 → x = 2. Wait — if initial concentrations are exactly [A]=[B]=1 at equilibrium, then x² = 4, x = 2.

The degree of dissociation of a weak acid increases when:

Answer: The solution is diluted with water

Dilution decreases the ion concentration, shifting equilibrium toward more dissociation and increasing the degree of dissociation.