1. Write a paragraph explaining how equilibrium is established.

The majority of chemical reactions that occur are “one-way” reactions. That is to say that the reactants (the left side of the equation) change into products (the right side of the equation). An example of this is the dehydration of sugar as evidenced by the video. The equation for this reaction is C₁₂H₂₂O₁₁(s) 12C(s) + 11H₂O(l). The sulfuric acid added to the sugar is only a catalyst and is not included in the reaction, but is located over the arrow.

Many other chemical reactions are “two-way” reactions, especially if they are in a sealed container. In these reactions, as the reactants are placed together they begin to move in the forward direction as in the “one-way” reactions because there are not any of the products yet. As more products begin to form, some of the products begin to work their way back up the “two-way” street and become reactants. An example of this process is the dimerization of nitrogen dioxide.

If brown nitrogen dioxide gas is placed into an evacuated glass container, molecules of the NO₂ gas begin to come together to form colorless N₂O₄ gas. It would be natural to assume that over time, the gas in the container would become colorless. However, upon careful observation, it becomes obvious that this does not occur. The intensity of the brown color begins to fade, but soon the color degradation stops. This happens when the rate of the forward reaction (the combination of the NO₂ molecules) exactly equals the rate of the reverse reaction (the separation of the N₂O₄ molecule). This is called the equilibrium. The equation for this occurrence is

NO₂(g) + NO₂(g) £ N₂O₄(g).

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