Reversible Reactions & Equilibria Flashcards

All 22 cards in this deck

What does the symbol $\rightleftharpoons$ mean in a chemical equation?

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

What colour change is seen when hydrated copper sulfate is heated?

Blue to white (hydrated $\mathrm{CuSO_4.5H_2O}$ to anhydrous $\mathrm{CuSO_4}$), and steam/water is given off.

What is observed when water is added to white anhydrous copper sulfate?

It turns blue again and heat is released.

What is meant by dynamic equilibrium?

The forward and backward reactions occur at the same rate, so the concentrations of reactants and products stay constant.

What condition must a reversible reaction be in to reach equilibrium?

A closed system - nothing can enter or leave.

True or false? At dynamic equilibrium both reactions have stopped.

False. Both reactions continue, but at equal rates, so concentrations stay constant.

What is the balanced equation for the formation of ammonia in the Haber process?

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

Where is the nitrogen for the Haber process obtained from?

From the air.

Where is the hydrogen for the Haber process obtained from?

From natural gas.

What temperature is used in the Haber process?

450 °C

What pressure is used in the Haber process?

200 atmospheres

What catalyst is used in the Haber process?

Iron.

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

False. The reaction is reversible and reaches a dynamic equilibrium, so only some is converted.

What are the steps to predict the effect of a temperature change on the position of equilibrium?

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

1. Identify which direction is exothermic: forward.
2. Cooling favours the exothermic direction (heating favours the endothermic one).
3. Equilibrium shifts right, so the yield of ammonia increases.

What are the steps to predict the effect of a pressure increase on the position of equilibrium?

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

1. Count moles of gas each side: 4 on the left, 2 on the right.
2. Increasing pressure shifts equilibrium to the side with fewer moles of gas.
3. Equilibrium shifts right, so the yield of ammonia increases.

What happens to the position of equilibrium if the concentration of a reactant is increased?

It shifts to the right (towards the products), so more product is formed.

What happens to the position of equilibrium if a product is removed as it forms?

It shifts to the right, making more product.

True or false? Increasing the pressure always increases the yield of product in a gaseous equilibrium.

False. It only shifts the equilibrium towards the side with fewer moles of gas; if both sides have equal moles there is no change.

True or false? Adding a catalyst increases the equilibrium yield of a reversible reaction.

False. The yield is unchanged; a catalyst only affects how quickly equilibrium is reached.

In $\mathrm{H_2(g) + I_2(g) \rightleftharpoons 2HI(g)}$ (iodine purple, HI colourless), what is observed if the equilibrium shifts to the right?

The colour becomes paler/fades, because there is less iodine.

What happens to the position of an equilibrium when the temperature is raised?

It shifts in the endothermic direction.

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 means unchanging, not the same amount of each substance.