Question

Would a newspaper bleaching in the sun be a physical or chemical change?

Asked by: David

Answer

Bleaching is usually an oxidation reaction, whether it is initiated by chemical bleach or photonically by ultraviolet rays in sunlight. The result is that the formerly colored ink or pigment loses its intensity and may eventually become almost white. The chemicals, which were originally colored, have been transformed into new chemicals. This is both a chemical and a physical change.

To be entirely general, all chemical changes or reactions are considered physical since all chemicals and their reaction products are physical. The converse of this is generally not true: most physical changes like bending a wire or lifting a block do not directly involve chemical changes. The wire and the block are chemically the same after the physical change.

An example of a chemical change that is obviously physical is the explosion of a mixture of gasoline and oxygen in air that propels most cars. The chemical reaction releases heat that causes the gasses to expand inside the cylinder and push the piston, ultimately rotating the crankshaft and finally the tires. The initial mixture of gasoline (a hydrocarbon) and oxygen are converted by the chemical reaction into water and carbon dioxide plus a number of undesirable pollutants including carbon monoxide, oxides of nitrogen and unburned hydrocarbons.

Answered by: Scott Wilber, President, ComScire - Quantum World Corporation

Search

Loading



Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department

Science Quote

'In a way science is a key to the gates of heaven, and the same key opens the gates of hell, and we do not have any instructions as to which is which gate. Shall we throw away the key and never have a way to enter the gates of heaven? Or shall we struggle with the problem of which is the best way to use the key?'

Richard Phillips Feynman
(1918-1988)

Deal of the Day

Image of Hover Craft Kit. Click on this image for more info. Hover Craft Kit
Regular Price: $29.99
Today's Price: $12.00
Learn the science behind hover craft technology with this cool kit! Buy it now! Deal ends at midnight!

Top Selling

Here are our physics & astronomy bestsellers:
Mini Plasma Ball
Slide Making Kit
Top Secret - Spinning Top
Wood Grain Newtons Cradle
Deluxe 3D Mirascope
Solar Radiometer
Periscope
Solar Science 4M Kit
Ultimate Chemistry Set CHEM C3000
3D Magnetic Field Tube