Identify all of the following that are chemical changes:
a. leaves turning color in the fall
b. dew forms on a blade of grass
c. ethanol evaporates
d. sugar dissolves in water
e. dry ice sublimes
f. charcoal burning

Answer : The correct options are, (a) and (f)

Explanation :

Chemical change : It is a change where changes occurs in the chemical composition and thus resulting in the formation of new compound or substance. It is an irreversible reaction.

The indication of chemical changes are :

Formation of gas bubbles.

Formation of precipitate.

Change in color.

Change in temperature.

Change in volume.

Change in smell or taste.

Evolution of heat, light and sound.

Physical change : It is a change in which shape and size of a substance changes. In this there is no change in the chemical composition of the substance and no new substance is forming. It is a reversible reaction.

The indication of chemical changes are :

Change in shape.

Change in form.

Change in size.

Change in phase.

(a) Leaves turning color in the fall : It is a chemical change.

(b) Dew forms on a blade of grass : It is a physical change because only changes takes place in the phase from vapor phase to liquid phase.

(c) Ethanol evaporates : It is a physical change because only changes takes place in the phase from liquid phase to vapor phase.

(d) Sugar dissolves in water : It is a physical change because only changes takes place in the phase from solid phase to liquid phase.

(e) Dry ice sublimes : It is a physical change because only changes takes place in the phase from solid phase to vapor phase.

(f) Charcoal burning : It is a chemical change. When charcoal burns, carbon reacts with oxygen to produce carbon dioxide and water as a product.

Hence, the correct options are, (a) and (f)

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.