. Explain with examples following characteristics of chemical reactions:   a. Change of colour  b. Evolution of gas  c. Change of smell  d. Change of state

See explanation.

Explanation:

Hello,

a. In this case, the change of color is evident for instance when copper reacts with nitric acid to form hydrogen and copper (II) nitrate since copper orange-like and nitric acid is colorless, but copper (II) nitrate is green (dry) or blue (hydrated).

b. In this case, when we make react hydrochloric acid and magnesium, we notice a gas giving off while the magnesium chloride remains aqueous, due to the fact that magnesium displaces hydrogen which is given off as a gas.

c. In this case, we can consider an egg since when it is edible it has a tasty smell but when it decomposes to rotten egg, hydrogen sulfide is given off due to the action of specific bacteria, causing a change in smell to a quite stinky one.

d. In this case, a reaction by which a change of state is exhibited is for instance when aqueous lead (II) nitrate reacts with aqueous potassium iodide to yield potassium nitrate which remains aqueous whereas the lead (II) iodide precipitates out as a solid due to its tiny solubility as a yellow solid.

Best regards.