Section 7.5 Assessment

Reviewing Concepts

1. What happens when a physical change does not go to completion? What happens when a reaction does not go to completion?

2. Once a chemical reaction has reached equilibrium, how does the system respond to change?

3. What does the double-ended arrow indicate in the following chemical equation?

   ${\mathrm{CaCO}}_{3 }\rightleftharpoons {\mathrm{Ca}}^{2+} + {{\mathrm{CO}}_3}^{2-}$

4. For which of the following reactions are both reactants and products likely to be found when the reaction appears to be complete? Explain.

   $$\begin{gathered} \mathrm{Mg} + {\mathrm{O}}_{2 }\to 2\mathrm{MgO} \\ \mathrm{HF} + {\mathrm{H}}_2\mathrm{O} \rightleftharpoons {\mathrm{H}}_3{0}^{+} + {\mathrm{F}}^{-} \end{gathered}$$

   5. Inferring Suppose the following reaction is allowed to come to equilibrium.

      $2{\mathrm{NO}}_2\left(g\right)\rightleftharpoons {\mathrm{N}}_2{\mathrm{O}}_4\left(g\right)$

      How will increasing the pressure on this system affect the amount of N₂O₄ formed?

   6. Using Models At 0°C, liquid water is in equilibrium with ice. Make a drawing of water molecules at this temperature, and describe what is happening.

   Connecting Concepts

   Phase Changes Write an equation for a system in which the sublimation and deposition of water have reached equilibrium. Use what you studied in Section 3.3 to explain what changes are happening.