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What is a chemical change?

What is a chemical change?

In a chemical change substances react to produce something new.

Chemical changes are also generally difficult to reverse.

Examples of chemical changes include

  • The burning of a match which produces smoke and ash.
  • The cooking of an egg. The protein of the egg white and yolk changes producing a solid.
  • The baking of a cake. During the baking process carbon dioxide gas is produced and the cake dough rises while changing to produce something new. 

In asking yourself whether a chemical change has occurred answer these two questions.

  • Has something new been produced?
  • Is the reaction difficult to reverse?

Some of the signs that may occur during a chemical change include

  • A permanent change in color
  • The production of a gas
  • The production of a light and or heat
  • The dissolving of a metal
  • The production of an insoluble solid. The word insoluble means that is doesn't dissolve.

When a red apple is sliced and left in the air it begins to go brown. There is a permanent change in color. The reaction is also difficult to reverse. So a chemical reaction has occurred.

If water is placed in a freezer it soon solidifies and becomes ice. The reaction is easily reversed by placing the ice in the sun. Since nothing new is formed and the reaction is easily reversed a chemical reaction has NOT occurred.