Difference Between Physical And Chemical Changes

What are the main differences between physical and chemical change ? & some examples please.

Expert Answers
gsenviro eNotes educator| Certified Educator

There are marked differences between physical and chemical changes.

Physical changes, typically, refer to changes in size, shape, texture, temperature, density, viscosity, etc. common examples include, change in volume of a material upon heating. Think what happens to a rubber ball that is heated or how welding is done (metal melts and solidifies when cooled). Think about the increase in viscosity of vehicle fuel during summer months (as compared to winter), thus leading to higher fuel efficiency (more miles per gallon of fuel). Similar is observed with honey, between summer and winter.

Physical changes do not lead to new substances being formed, which is a typical property of chemical changes. Here new bonds are formed between molecules, leading to new substances. Think about burning of leaves  leading to generation of gases or how plants grow and lead to fruits. Some other examples include rusting of iron, burning of oil (in cooking, vehicle operation, etc.), rotting of fruits, etc.

Pls. note that many of these changes are reversible, both physical and chemical. Examples are melting and re-solidification of metals upon heating and cooling. Similarly, chemical compounds may be formed reversibly (although not that easily manifested to casual observer). Chemical reversibility or cycling is more easily observed with nutrient cycling in nature. A common example is wwater cycle in nature. 

good luck.

aishukul | Student

Physical change means changing a substance's form but not a substance's chemical composition. A substance changing from a solid to a liquid (or vice versa) is an example of a physical change. Other examples include melting an ice cube (an ice cube is solidified water and it will still be water in the liquid state too), and tearing paper. Tearing paper changes the paper from being a larger piece to becoming smaller bits of pieces. It still stays as paper but now it's in smaller pieces. 

Chemical Change is irreversible and it's where substances are altered through chemical reactions and change into a different substance. Furthermore, some substances will change in color or produce an odor when a chemical change has occurred. A rusting nail is an example of a chemical change. The nail is made out of metal. When it gets exposed to oxygen over long period of time, it starts to rust due to the oxygen reacting with the metal particles. This shows the change in color from the nail initially being a dark gray to turning into a reddish, brown colored nail.

fyend | Student

Physical change is reversible change in which the substance changes form and rearranges molecules but maintains its chemical composition. Changes include change of state, shape, temperature, color, and texture. Often, a change in a physical property such as luster, malleability, mass, volume, solubility, density, viscosity, etc. is referred to as a physical change.

Examples include dissolving sugar in water, boiling water, chopping up vegetables, 

Chemical change, on the other hand, is irreversible change in which a new substance is formed that has a different chemical composition than the starting materials. It involves breaking bonds between atoms and forming new bonds. Change in temperature and color, different odor, formation of a precipitate or bubbles indicate chemical change. However, a change in color is not necessarily chemical change.

Some examples of chemical change are rusting iron, burning gasoline, souring milk, cooking eggs, and rising bread.

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