Chemical vs. Physical Change

Instructor: Danielle Reid

Danielle has taught middle school science and has a doctorate degree in Environmental Health

From watching ice melt into water to observing a plant change its colors, changes in matter are important to science and nature. Learn about physical and chemical changes and why they are uniquely different from each other.

Why Change Matters

You may have seen a magician change a white scarf into a white bunny using just a hat. Did you know this 'trick' can also be viewed in the science laboratory or even in nature? Poof! Just like that we can easily change a material from one form to another. Well, its not as easy as poof, but a similar, seemingly magical process is certainly possible.

Now you may be asking why is change even important in science and nature? Great question! Let's take our eyes away from the computer screen for a minute and look around. What do you see? Maybe you see the table you are working on or the chair you are sitting in. Everything around you, both indoors and outdoors, can be referred to as matter.

Whatever the source of the change, whether nature or a scientist conducting an experiment, changes to matter are always occurring. These changes greatly influence the many experiences we stumble upon in life.

What is a Chemical Change?

When a new chemical substance or material is formed it's called a chemical change. For a chemical change to occur the substance must change on a molecular level. This usually means chemical bonds between molecules in a substance are either broken or formed during a chemical change.

Note that chemical changes are irreversible. Once you commit to a chemical change you cannot go back and reverse these changes. Now you may be wondering what causes a chemical change? A chemical change is often generated from a chemical reaction or process. When identifying chemical changes there are a few key hints to remember.

  • Chemical changes produce one or multiple new substances from a chemical reaction
  • Characteristics such as smell, light, gas, heat, or color can indicate a chemical change
  • Chemical changes can form solid substances called precipitates.

Would you believe that, on average, we witness daily chemical changes without realizing it? This is certainly true! For example, take a nice cozy fireplace. As the wood crackles and burns it eventually turns to ashes. Burning wood in the presence of oxygen, drives a chemical reaction that produces heat, smoke, and ashes.

Example of a Chemical Change

By classifying ashes as a type of matter created, we can confidently suggest a chemical change took place during the fire. Would you suppose this process is reversible? Not at all! There is absolutely no way we can convert those ashes back into our original piece of wood.

What is a Physical Change?

Contrarily, changing a substance without altering its internal makeup is a physical change. A very simple way to remember a physical change is to see if the form has changed in the substance or material. In other words, if we look on a molecular level, there will not be any bonds broken or formed. Instead, this substance or material will simply change on the outside into something else. Listed below are a few hints to consider when identifying physical changes.

  • Changes to the molecular identity of a substance do not occur
  • A phase change in matter (like going from a liquid to a solid) occurs

Physical changes can be reversible in some cases. One example is making ice cubes. If you freeze liquid water to ice, it can melt back into a liquid again (assuming you allowed the temperature to change, say by taking them out of the freezer!). The molecular structure remains the same, only the form has changed.

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