Chemical change
Chemical change is any change that
results in the formation of new chemical substances. Chemical change involves
making or breaking of bonds between atoms. These changes are chemical:
Example of chemical change
Example of chemical change
- burning wood
- dissolving salt in water
- mixing acid and base
- digesting food
- iron rusting (iron oxide forms)
- gasoline burning (water vapor and carbon dioxide form)
- eggs cooking (fluid protein molecules uncoil and crosslink to form a network)
- bread rising (yeast converts carbohydrates into carbon dioxide gas)
- milk souring (sour-tasting lactic acid is produced)
- suntanning (vitamin D and melanin is produced)
Physical change
Physical change is any change where
no new substances are formed. Physical changes involve states of matter and
energy. Physical changes occur when substances are mixed, but don't chemically
react
Some examples of physical change
are:
- crumpling a sheet of paper
- melting an ice cube
- casting silver in a mold
- whipping egg whites (air is forced into the fluid, but
no new substance is produced)
- boiling water (water molecules are forced away from
each other when the liquid changes to vapor, but the molecules are still H2O.)
- dissolving sugar in water (sugar molecules are
dispersed within the water, but the individual sugar molecules are
unchanged.)
- dicing potatoes (cutting usually separates molecules
without changing them.)
- mixing sand and water
- breaking a glass