Anhydrous cobalt(II) chloride (blue powder) reacts with water to produce hydrated cobalt(II) chloride (pink crystals). When hydrated cobalt(II) chloride is heated, it turns back into anhydrous cobalt(II) chloride and water vapor.

Which two words describe the reaction of anhydrous cobalt(II) chloride with water?

• Condensation
• Endothermic
• Exothermic
• Neutralisation
• Reversible

In a closed system at a constant temperature, sulfur dioxide gas (${SO}_2$) reacts with oxygen gas ($O_2$) to form sulfur trioxide gas (${SO}_3$).

The equation for this reversible reaction is:

$2{SO}_2(g)+O_2(g)\rightleftharpoons 2{SO}_3(g)$

Which statement describes this reaction system once it has established dynamic equilibrium?

• The forward and reverse reactions occur at the same rate.
• The rate of the forward reaction is greater than the rate of the reverse reaction.
• The rate of the forward reaction is less than the rate of the reverse reaction.