Anhydrous cobalt(II) chloride is a blue solid. When water is added, it turns into pink hydrated cobalt(II) chloride, releasing heat. Upon heating, the pink crystals turn back into the blue anhydrous solid and water vapor.

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

• Thermal decomposition
• Exothermic
• Oxidation
• Reversible
• Precipitation

In a sealed container, sulfur dioxide gas (${SO}_2$) reacts with oxygen gas ($O_2$) to establish an equilibrium with sulfur trioxide gas (${SO}_3$).

The chemical equation for this reaction is:

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

Which sentence describes this reaction when it has reached dynamic equilibrium?

• The rate of the forward reaction is faster than the rate of the reverse reaction.
• The forward and reverse reactions proceed at the same rate.
• The rate of the forward reaction is slower than the rate of the reverse reaction.