 In chapters 5 and 8, you observe many reactions that were very exothermic. You saw the reaction of potassium in water. One of the most difficult terms to deal with in chemistry is the term spontaneous. When we place potassium metal in water, we get a very rapid reaction and we say that the reaction is spontaneous. Other reactions such as the reaction of hydrogen and oxygen may proceed at such a slow rate at room temperature as it seems to be not occurring at all. If we mix hydrogen and oxygen in a balloon, nothing seems to happen at room temperature. We might initially say that this reaction is non-spontaneous. If we bring in a flame, a very rapid reaction occurs. The reaction is spontaneous. It just needed the right conditions to proceed rapidly. In this chapter, you will learn the real meaning of the term spontaneous and non-spontaneous. You will learn to predict which reaction should and should not occur.