Chemical Changes

It's the F ourth of July in Providence, Rhode Island. Brilliant fireworks are exploding in the night sky. When you look at the fireworks, you see dazzling sparkles of red, white and blue trickle down in all directions. The explosion of fireworks is an example of chemical change. During a chemical change, substances are changed into different substances . Another words, the composition of the substance changes.

Signs of Chemical Changes How can you tell whether a change is a chemical change? If you think you are unfamiliar with chemical changes, think again. Physical changes are relatively easy to identify. If only the form of a substance changes, you have observed a physical change. A common physical change occurs when matter changes from one phase to another. When an ice cube melts for example, it becomes liquid water. The solid ice and liquid water have the same composition. The only difference is the form.

C ol o r Changes As in the case of autumn leaves, a change in color is a clue to indicate a chemical change. Perhaps you have found a half eaten apple that turns brown. The reason is that a chemical change has occurs when food spoils. You have just witnessed a spectacular chemical change if you have seen the leaves change color in the autumn.

When you bake a cake, energy is absorbed by the batter as it changes form a runny mix into a cake. Energy - Absorbed or Released Another sign of a chemical change is the release or gain of energy by an object. Many substances absorb energy to undergo a chemical change. Energy is absorbed during chemical changes involved in cooking, like baking a cake.

Energy can also be released during a chemical change. The fireworks that were mentioned above release energy in a form of light that you can see. You can also see that energy is released when in this movie clip when sodium and chlorine are combined with water.

Odor Changes It only takes one experience with a rotten egg to learn that they smell different that fresh eggs. When eggs and food spoil, they undergo a chemical change. The change in odor is a clue to the chemical change . When you smell an odd order in foods such as chicken, pork of mayonnaise, you know that the food has undergone a chemical change. You can use this clue to avoid eating spoiled food and becoming ill.

Production of Gases or Solids The formation of a gas is a clue to chemical changes. The bubbles of gas that you observed form when an antacid is dropped into water is an example of change. Another clue that a chemical change has occurred is the formation of a solid. A solid that separates out of solution during a chemical change is called a precipitate.

As wood burns, it turns into a pile of ashes and gases that rise into air. After the wood is burned, it cannot be restored to its original form as a log. Not easily reversed How do physical and chemical changes differ from each other? Think about ice for a moment. After ice melts into liquid water, you can refreeze it into solid ice if the temperature drops. Freezing and melting are physical changes. The substances produced during chemical changes however cannot easily change back into the original substances.

Chemical vs Physical Change The most important thing for your to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change.

Chemical Reactions Chemical Changes are also called Chemical Reactions. Chemical reactions involve combining different substances. The chemical reaction produces a new substance with new and different physical and chemical properties. Matter is never destroyed or created in chemical reactions. The particles of one substance are rearranged to form a new substance. The same number of particles that exist before the reaction exist after the reaction.