Select the equations below that represent physical changes.

Choose one or more:

A.

2 H2O (l) → 2 H2 (g) + O2 (g)

B.

H2O (l) → H2O (s)

C.

CO2 (s) → CO2 (g)

D.

H2 (g) → 2 H (g)

Physical changes - any change in the physical properties of the substance is a physical change. Generally physical properties include color, state, size, shape, odour, appearance. In any phyical change, no new substance is formed.

Chemical changes - any change in the chemical properties of the substance is a chemical change. Chemical properties changes only when something new is formed during a reaction.

∴ Part A - 2 H2O (l) → 2 H2 (g) + O2 (g)

In this, H2 and O2 is produced during the reaction which is different from H20. Thus, it is a chemical change.

Part B - H2O (l) → H2O (s)

In this, only the state of water changes from liquid to solid and no new product is formed. Thus, it is a physical change.

Part C-CO2 (s) → CO2 (g)

In this also, only the state of CO2 changes from solid to gas and no new product is formed. Thus, it is a physical change.

Part D-H2 (g) → 2 H (g)

In this reaction, H2 molecule is dissociated into 2 hydrogen atom leading to formation of new products. Thus, it is a chemical change.

Finally, equations that represent physical changes are - B and C

B. H2O (l) → H2O (s)

C. CO2 (s) → CO2 (g)