What is the Difference Between a Chemical Change

What is the Difference Between a Chemical Change and a Physical Change?

Physical Change Physical changes occur when objects undergo a change that does not change their chemical nature. A physical change involves a change in physical properties. Physical properties can be observed without changing the type of matter. Examples of physical properties include: texture, shape, size, color, odor, volume, mass, weight, and density.

Examples of a Physical Change • Piece of paper ---- Rip It ---- Still a Piece of paper

Chemical Change Chemical changes are changes substances undergo when they become new or different substances. For example, the fireworks we see on the 4 th of July are actually metals such as magnesium and copper that change chemically as they light up the night skies with their fantastic colors. To identify a chemical change look for observable signs such as color change, bubbling and fizzing, light production, smoke, and presence of heat. Click on the candle and observe:

Examples of 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.

Examples of a Chemical Change • The explosion of fireworks is an example of chemical change

Clues that a Chemical Change Happened • 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

Clues that a Chemical Change Happened • Production of Gases 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.

Clues that a Chemical Change Happened • Production of Gases or Solids 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 Here, sodium iodide (Na. I) is added to lead(II) nitrate (Pb(NO 3)2). The result is a bright yellow precipitate

Clues that a Chemical Change Happened • 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.