Evaporation in a swamp cooler simply involves the conversion of water in the liquid state to water in the gaseous state. It is an easily reversible process if the vapour can be collected and condensed. A chemical change involves the formation of a new substance and is not easily reversible. It is a chemical reaction. A dry cell operates by a chemical change which produces voltage in the cell. Digestion involves a series of irreversible chemical reactions catalysed by enzymes. Hence the answer.
