# 2.16: Chemical Properties and Chemical Reactions


### Have you ever left your bicycle out in the rain?

It's not a good idea because the rain can cause the bicycle to rust. You start to get a reddish-orange build-up of a rough deposit on the metal. It may start with the chain, but can spread to other parts of the bicycle, especially if there are scratches that create a bare metal surface. The formation of rust is a chemical process that takes place when iron is exposed to water and oxygen. It is estimated that damage due to rust costs U.S. businesses, military, and government over 276 billion dollars a year—a very expensive chemical process.

## Chemical Properties

A chemical property describes the ability of a substance to undergo a specific chemical change. A chemical property of iron is that it is capable of combining with oxygen to form iron oxide, the chemical name of rust. The more general term for rusting and other similar processes is corrosion. Other terms that are commonly used to describe chemical changes are: burn, rot, explode, decompose, and ferment. Chemical properties are very useful in identifying substances. However, unlike physical properties, chemical properties can only be observed as the substance is in the process of being changed into a different substance.

## Chemical Change

A chemical change is also called a chemical reaction. A chemical reaction is a process that occurs when one or more substances are changed into one or more new substances. Zinc $$\left( \ce{Zn} \right)$$ is a silver gray element that can be ground into a powder. If zinc is mixed at room temperature with powdered sulfur $$\left( \ce{S} \right)$$, a bright yellow element, the result will simply be a mixture of zinc and sulfur. No chemical reaction occurs. However, if energy is provided to the mixture in the form of heat, the zinc will chemically react with the sulfur to form the compound zinc sulfide $$\left( \ce{ZnS} \right)$$. The figure below shows the substances involved in this reaction.

Alkaline metals are highly reactive with water. Watch the video to see what happens when different alkaline metals are exposed to water.

## Summary

• A chemical property describes the ability of a substance to undergo a specific chemical change.
• A chemical reaction is a process that occurs when one or more substances are changed into one or more new substances.

## Review

1. What is a chemical property?
2. What is a chemical reaction?
3. When can we observe a chemical property?
4. Is freezing water a chemical property?

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