Answer:

(a) A chemical reaction is a process that occurs when reactants react to generate new material. It is defined by the evolution of a gas, color change, precipitate formation, temperature change, and state change.

(b)

(i) Carbon Dioxide Gas Evolution

(ii) Color change from purple to colorless

(iii) Formation of a white barium sulphate precipitate

(iv) Temperature change, an exothermic response

(v) Transition from solid to liquid and gaseous states