The reaction of lead acetate and potassium iodide
has the experience of phase transformation of the two. When lead acetate meets potassium iodide, there is a definite formula for its transformation.

When the two are mixed in liquid phase, a chemical change occurs. Lead acetate is separated into ions in water, and so is potassium iodide. Lead ion ($Pb ^ {2 +} $) and iodine ion ($I ^{ - }$） phase, then lead iodide ($PbI_ {2} $) precipitate, yellow and brilliant, suspended in the liquid, the shape is very different. In addition, the rest are acetate ions ($CH_ {3} COO ^{ - }$） and potassium ions ($K ^{ + }$） still exist in the liquid, and they are mixed in the middle.

The formula for the reaction can be written as: $Pb (CH_ {3} COO) _ {2} + 2KI = PbI_ {2}\ downarrow + 2CH_ {3} COOK $. This formula specifies the change of quality and quantity of the phase of the two, which shows the wonder of chemistry. The phase of matter has its own number and cannot be controlled. Looking at this reaction, it can be seen that the change of chemistry, between micro-particles, the change of quality and state is a natural wonder, and the reason is endless.