Reversible Reactions & Equilibria Flashcards

All 15 cards in this deck

What does the symbol ⇌ mean in a chemical equation?

The reaction is reversible — it can go in both the forward and backward directions.

What is meant by dynamic equilibrium?

The forward and backward reactions happen at the same rate in a closed system, so the concentrations of reactants and products stay constant.

Write the balanced equation, with state symbols, for the formation of ammonia in the Haber process.

$\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$

In the Haber process, where are the nitrogen and the hydrogen obtained from?

Nitrogen from the air; hydrogen from natural gas.

State the three conditions used in the Haber process.

450 °C, 200 atmospheres, and an iron catalyst.

True or false? In the Haber process all of the nitrogen and hydrogen are converted into ammonia.

False. The reaction is reversible, so an equilibrium mixture of nitrogen, hydrogen and ammonia is formed.

Which way does the position of equilibrium shift when the temperature is decreased?

e.g. $\mathrm{N_2 + 3H_2 \rightleftharpoons 2NH_3}$, forward reaction exothermic

In the exothermic direction, to oppose the temperature reduction.

e.g. it moves to the right, towards ammonia, increasing the yield.

Which way does the position of equilibrium shift when the pressure is increased?

e.g. $\mathrm{N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)}$

Towards the side with fewer molecules of gas.

e.g. 4 molecules on the left, 2 on the right, so it moves right towards ammonia.

Which way does the position of equilibrium shift when the concentration of a reactant is decreased?

e.g. chloride ions removed from: pale blue solution + chloride ions ⇌ yellow solution + water

To the left-hand side, towards the reactants.

e.g. the mixture turns blue.

True or false? Adding a catalyst increases the yield of product at equilibrium.

False. A catalyst does not change the position of equilibrium; it only makes equilibrium be reached faster.

True or false? At dynamic equilibrium the concentrations of reactants and products stay constant, but they are not necessarily equal to each other.

True. Constant concentrations do not mean equal amounts of reactants and products.

How can you show that this reaction is reversible?

e.g. $\mathrm{CuSO_4 \cdot 5H_2O \rightleftharpoons CuSO_4 + 5H_2O}$

Heat the blue hydrated crystals: they turn white as water is given off. Add water to the white anhydrous solid: it turns blue again.

True or false? Adding water to white anhydrous copper sulfate releases heat.

True. The reverse reaction gives out heat and the solid turns blue again.

Which equilibria have their position changed by a change in pressure?

Only those involving gases, where the two sides have different numbers of gas molecules.

What does it mean if an equilibrium 'lies to the right'?

The equilibrium mixture contains more products than reactants.