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CC0. Rusty Truck. Rust is a chemical reaction that changes useful objects into things that can no longer be used. Courtesy of Needpix

As you learned in the previous activity, matter may change its physical state but it does not change the way it is made up of particular molecules. The movement of the molecules may be faster or slower depending on the physical state the matter is in, but it is still the same substance. In this activity, you will learn about chemical change.

Chemical change means that there is a change to the actual chemical structure of the substance. A new substance is produced. As with physical change, the substance may look different. However, unlike a physical change, a new arrangement or combination of the atoms that make up the substance occurs so that the substance is something different than it was before the chemical reaction.

Sugar is white and tastes sweet (taste is a chemical property). When sugar burns it undergoes change. It is black and no longer has the same flavour. Energy is released as it burns.

CC0. Sugar burning. Courtesy of Needpix

When a physical change takes place, the substance remains the same but the state it is in has changed (e.g., water turns to ice). When a chemical change occurs, a reaction happens between two or more elements or substances. After the reaction, the result is two or more products that are different than those you began with.

A substance that undergoes a chemical change will have different physical properties as well as different chemical properties after the change. This means that it is no longer the same substance it used to be!

You know that a physical change in matter means that it changes its state (gas, liquid, or solid) but not its composition (what it is made of). A chemical change, as you just learned, means that a substance becomes something else. It not only changes its physical state, but its composition; its molecules are rearranged.

For a chemical change to take place, two or more materials react with each other and end up creating something new or different. We can look for several things to help us know if a chemical change has taken place.

Change in colour: You may have discovered that bleach reacted with the dye in your red Calgary Flames jersey and turned it pale pink!
Change in smell: You probably have struck a match before. The substances in it reacted, and you smelled sulfur.
Change in heat: In a chemical reaction, heat is either given off (released) or taken in (absorbed). A car's engine burns fuel, and after the motor has been running, you can feel the heat on the hood of the car.
Sound: Sometimes a chemical change may be indicated by sound, such as when you hear the explosions as fireworks go off.
Light: A burning candle produces light as part of the chemical reaction.
Formation of a gas or solid: When vinegar (a liquid) and baking soda (a solid) are mixed together, the chemical reaction produces carbon dioxide (a gas).

Sometimes, to tell whether a change in state of matter is physical or chemical just by looking for these clues is difficult. Some materials may need to be analyzed in a lab to determine the kind of change that took place.

A general rule to help us to remember the difference between a physical change and a chemical change is that physical changes are easy to reverse. For example, you can melt an ice cube and freeze the water again. A chemical change results in new products, so the change cannot easily be reversed.

Click on the Play button below to watch a video that shows some amazing chemical reactions!

You know that matter can be identified by its physical properties. In addition, matter can also be identified by its chemical properties.

Physical properties are those we can determine by using our senses: what the substance looks, smells, feels, or tastes like. Chemical properties are the features of a substance that allow it to react with certain substances or prevent it from reacting with certain substances.

The last activity reviewed a list of physical properties matter might have. The chemical properties of matter cannot be so easily listed because the chemical properties of chemical reactions vary depending on the substances involved. However, some chemical reactions are more common, and knowing them can help you see and identify their chemical properties.