Write chemical equations to represent the following reactions.

(a) Calcium phosphate is heated with silicon  dioxide and carbon, producing calcium silicate (CaSiO₃), phosphorus (P₄), and carbon monoxide. The phosphorus and chlorine react to form phosphorus trichloride, and the phosphorus trichloride and water react to form phosphorous acid.

(b) Copper metal reacts with gaseous oxygen, carbon dioxide, and water to form green basic copper carbonate, Cu₂(OH)₂CO₃ (a reaction responsible for the formation of the green patina, or coating, often seen on outdoor bronze statues).

(c) White phosphorus and oxygen gas react to form tetraphosphorus decoxide. The tetraphosphorus decoxide reacts with water to form an aqueous solution of phosphoric acid.

(d) Calcium dihydrogen phosphate reacts with sodium hydrogen carbonate (bicarbonate), producing calcium phosphate, sodium hydrogen phosphate, carbon dioxide, and water (the principal reaction occurring when ordinary baking powder is added to cakes, bread, and biscuits).