Physical changes are changes in the form or appearance of a substance without a change in its chemical composition. In the case of ethyl alcohol evaporation, the liquid alcohol changes into a gas, but the chemical composition of the alcohol remains the same. The molecules of alcohol are still C2H5OH, and they are still held together by the same chemical bonds.

Chemical changes, on the other hand, involve a change in the chemical composition of a substance. This can happen when atoms are rearranged, removed, or added to a molecule. For example, when ethyl alcohol is burned, it undergoes a chemical change to produce carbon dioxide and water. The carbon atoms in the alcohol are rearranged to form carbon dioxide, and the hydrogen atoms are combined with oxygen to form water.