(POM) Changes of Matter Lesson
Changes of Matter
As we discussed, the matter is all around us. However, that doesn't mean that matter stays the same. Matter can undergo physical changes and chemical changes. Please watch the videos below to hear an explanation of the difference between physical and chemical changes as well as have some visual examples of each.
Physical Changes
A physical change is one where the particles of the substances that are involved in the change are not broken up in any way. When water is heated, for example, the temperature and energy of the water molecules increases, and the liquid water evaporates to form water vapor. When this happens, some kind of change has taken place, but the molecular structure of the water has not changed. This is an example of a physical change. All changes in state are physical changes.
H2O( ℓ ) → H2O(g)
Conduction (the transfer of energy through a material) is another example of a physical change. As energy is transferred from one material to another, the energy of each material is changed, but not its chemical makeup. Dissolving one substance in another is also a physical change.
There are some important things to remember about physical changes in matter:
- Arrangement of Particles
When a physical change occurs, the compounds may re-arrange themselves, but the bonds between the atoms will not break. For example, when liquid water boils, the molecules will move apart but the molecule will stay intact. In other words, water will not break up into hydrogen and oxygen atoms.
The picture below shows this phase change. Note that the water molecules themselves stay the same, but their arrangement changed. As you heard in the video above, when water boils the gas released is not hydrogen and oxygen gas but water vapor. Hydrogen gas and Oxygen gas are very volatile and would be very dangerous to be around.
- Conservation of Mass
In a physical change, the total mass, the number of atoms and the number of molecules will always stay the same. In other words, you will always have the same number of molecules or atoms at the end of the change as you had at the beginning.
- Energy changes
Energy changes may take place when there is a physical change in matter, but these energy changes are normally smaller than the energy changes that take place during a chemical change.
- Reversibility
Physical changes in matter are usually easier to reverse than chemical changes. Methods such as filtration and distillation can be used to reverse the change. Changing the temperature is another way to reverse a physical change. For example, a mixture of salt dissolved in water can be separated by filtration; ice can be changed to liquid water and back again by changing the temperature.
Look at the picture below for some additional examples of physical changes. In each example, matter may look different after the change occurs, but it's still the same substance with the same chemical properties. For example, smaller pieces of wood have the ability to burn just as larger logs do.
Physical Changes description Links to an external site.
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