1. This energy diagram is for the thermal decomposition of solid mercury (II) oxide (also known as mercuric oxide) into liquid mercury and oxygen gas. A graph. The x-axis is labeled Reaction pathway. The y-axis is labeled Energy. A dashed horizontal line labeled Reactants is plotted at about one-fifth across the y-axis. A dashed horizontal line labeled Activated complex is plotted near the top of the y-axis. A line labeled Products is plotted on the graph. Products starts at the origin of Reactants, extends horizontally to the right, curves upward to the right with downward opening until Activated complex, slightly curves downward to the right, and extends horizontally to the right. The distance between Reactans and Activated complex is labeled (a).

• Write a balanced equation for the reaction.
• Explain what feature is shown by the arrow labeled (a).
• Using chemical symbols and dashed lines (this can be done with type), draw what the activated complex or transition state might look like.
• Is this reaction exothermic or endothermic? Explain.