The tearing of paper is physical as it's still paper even when you tear it. A chemical reaction is when the substance is chemically change. ... When paper is burn, the cellulose in the air reacts with the oxygen to form carbon dioxide and water.
Therefore it's chemistry.
It would be physics, if a physical change was occuring to the paper while burning it. It would be biology if it was related to life. But, the main changes are chemical:
While burning paper you change it's composition by creating an interaction between the components of paper and the heat released by the fire. In this reaction we'll see how CO2 affects the composition of paper.
Hope it helped,
BioTeacher101
