Chemical Equations — Important Questions

Formation of new substances, Change in color, Gas evolution, Heat liberation or absorption

Chemical changes involve formation of new substances with different properties. They may show color change, gas evolution, heat changes, or precipitate formation. Change in shape only is a physical change.

2

The coefficient of H₂O is 2, which means 2 molecules of water are formed. Coefficients show the number of formula units involved in the reaction.

(s) for solid, (l) for liquid, (g) for gas, (aq) for aqueous

Physical states are indicated by (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution. There is no standard symbol (p) for precipitate.

Gas evolution

The upward arrow (↑) or (g) indicates that a gas is evolved or released during the chemical reaction.