Anhydrous copper(II) sulfate (white powder) reacts with water to produce hydrated copper(II) sulfate (blue crystals). Hydrated copper(II) sulfate can be heated to turn back into anhydrous copper(II) sulfate and water vapor.

Which two words describe the reaction of anhydrous copper(II) sulfate with water?

• Combustion
• Exothermic
• Neutralisation
• Precipitation
• Reversible

In a closed system, nitrogen dioxide gas (${NO}_2$) exists in equilibrium with dinitrogen tetroxide gas ($N_2{O}_4$).

The equation for this reversible reaction is:

$2{NO}_2(g)\rightleftharpoons N_2{O}_4(g)$

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

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