Change

Chemical or Physical

Reason

Steel wool turned the blackened pot silver

Lightning flashed across the sky

Acid caused the limestone to fizz

The  wooden steps rotted

Lemon juice turned the tea cloudy

A puddle of gasoline dried, but left a bad odor

Gravy in the refrigerator gelled

A blue-green lobster turned red as it cooked

A cavity formed in a tooth

Flash cameras flashed after the wedding

Ice cubes shrink in the freezer

A raw egg became a cooked egg

A piece of paper became ash

Mothballs gradually disappeared

The steel railing rusted

A silver spoon tarnished

The copper pot turned green

A rubber band is stretched

The baseball smashed the window