Physical and Chemical Changes
By: Doris Hoyos and Priya Vanparia
Introduction
Have you ever wondered why fireworks "boom" after they are shot in the sky? Or why your ice cream drips in the summer heat? These occurrences are caused by chemical and physical changes. In this unit we will discuss what these changes are, and how we can identify them.
Physical Change
Physical Change is an alteration that only changes the appearance of a substance, and not the actual substance itself. During this process, compounds are rearranged but are not changed internally. Most physical changes alter the size and shape of a substance, and are reversible.
Melting Popsicle
When a popsicle melts in a hot summer day, it changes size and shape, but does not change into a new substance. Compounds are only rearranged from a solid to a gas.
Shredded Paper
When paper is shredded, no new products are formed. It's size and shape are the only things that change into different figures.
Crushed Soda Can
When a soda can is crushed in half, it will change its size and shape but nothing else.
Chemical Change
Chemical Change is an alteration that produces a new substance. During this process reactants change into new products, and compounds are either formed or broken. Most chemical changes are irreversible.
Indications of Chemical Change
Indications of Chemical Change
- Change in color, smell, or temperature
- Production of energy in light, sound, movement or and gas form.
- Formation of a precipitate (solid particles separated from the solution)
Fried Egg
When you fry an uncooked egg, the clear liquid part will become solid (precipitate) and change into a white color.
Rusty Pennies
As pennies become older, their copper will combine with oxygen (reactants), and form a new substance with different colors.
Fireworks
When a firework is shot into the sky, it produces light and sound, indicating a chemical change.
Questions
- What happens to compounds during a chemical change?
- Is a snowman melting a physical or chemical change?
- True or False: Change in size or shape is an indication of chemical change.
- Is the baking of a cake a chemical or physical change?
- True or False: A physical change is reversible.