Phosphorus tribromide

PBr3, a corrosive, fuming, colourless liquid with penetrating aroma; soluble in acetone, alcohol, carbon disulphide, and hydrogen sulfide; decomposes in water; used as an analytical reagent to test for sugar and oxygen.

Phosphorus trichloride

PCI3, a colorless, fuming liquid that decomposes rapidly in moist air and water; soluble in ether, benzene, carbon disulfide, and carbon disulfide, and carbon tetrachloride; boils at 76˚C; used as a chlorinating agent, phosphorus solvent and in saccharin manufacture.

Phosphorus tri-iodide

PI3, hygroscopic, red crystals, melting at 61˚C; soluble in alcohol and carbon disulphide; decomposes in water; used in organic synthesis.

Photosynthesis

the chemical process by which green plants synthesize organic compounds from carbon dioxide and water in the presence of sunlight. It occurs in the chloroplasts (most of which are in the leaves) and there are two principal series of reactions. In the light reactions, which require the presence of light, energy from sunlight is absorbed by photosynthetic pigments (chiefly the green pigment chlorophyll) and converted into chemical energy.

Photosynthetic pigments

the plant pigments responsible for the capture of light energy during the light reactions of photosynthesis. The green pigment chlorophyll is the principal light receptor, absorbing blue and red light. However, the carotenoids and various other pigments also absorb light energy and pass this on to the chlorophyll molecules.

Physical change

a change to a substance that does not alter its chemical properties.