Tag: phenomena around us

Dissolving sugar in water is a physical change because sugar molecules are dispersed within the water, but the individual sugar molecules are unchanged.

Since the law of conservation of mass is valid under all circumstances, hence, mass always remains the same, whether a substance undergoes physical change or chemical change. 

A plant collecting sunlight and turning it into food is a photosynthesis reaction which is an example of a photochemical reaction. This is a chemical change. 

A change in temperature is characteristic of a chemical change. When the reactants are mixed, the temperature change caused by the reaction is an indicator of a chemical change. 

Solid ammonium chloride vapourizes to form gaseous ammonium chloride. This is a physical change. Ammonium chloride is partially dissociated. This a chemical change. The products ammonia and chlorine recombine to form ammonium chloride. This is also a chemical change.

On burning candle, wax melts which is a physical change. Also, the wax near the flame burns and gives $CO _2$, soot, light and heat which is a chemical change. Hence, burning of candle is a physical as well as chemical change.

Physical change does not involve formation of new products. As cutting of trees do not produce anything it is said to be a physical change.

The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances. In a physical change, there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition. 

The texture of a substance can differ with a physical change. For example, if a piece of wood was sanded, waxed, and polished, it would have a very different texture than it initially had like a rough piece of wood. Although, we cannot see temperature change, unless if a change of state is occurring, so it is a physical change.