General Chemistry/Physical Change
Physical changes in chemistry include phase changes and anything else that changes the way that matter is arranged in space.
Examples of physical changes are:
- breaking a stick
- crushing ice
- melting ice
- stretching a rubber band
- boiling water
A phase change is a change from one phase to another. The most common example is liquid water freezing into ice or evaporating into a gas. Phase changes result in different properties for the substance changing phases but the chemical identity of the material does not change. In the case of water, its molecules are always composed of two hydrogen atoms bonded to one oxygen atom. However, in frozen water the molecules are frozen into place in relation to each other in a structure called a crystal; in liquid water the molecules flow relative to each other; and water molecules in the gas phase are flying freely in space and seldom even contact each other.
Phase changes are controlled by temperature and pressure. By lowering the temperature of a gas it can be condensed into a liquid and then even into a solid. Heating a solid melts it into a liquid and then, with further heat, into a gas.