Science Experiments | Chemical Properties - Introduction

Introduction

How many ways can you describe a substance? Two common ways are by listing its physical properties and its chemical properties. A physical propertyA characteristic that you can detect with your senses, such as color and shape. is a characteristic of a substance that you can detect with your senses, such as its color, shape, size, smell, taste, texture, temperature, density, or volume. For example, a lemon is yellow, oval-shaped, and smaller than a grapefruit. It has a sharp smell and a rough texture.

A physical changeA change in which the substance keeps its molecular identity, such as a piece of chalk that has been ground up. changes a physical property but does not change the identity or molecular makeup of the substance. One example of a physical change is salt crystals dissolving in water, which changes their shape. When the water evaporates, you can see the salt crystals again, unchanged by being dissolved in the water. Tearing paper into small pieces is also a physical change. The bits of paper look different, but they are still composed of the same molecules as when they were joined together.

A chemical propertyA characteristic of a substance that allows it to undergo a chemical change. Chemical properties include flammability and sensitivity to light. is the ability of a substance to react with other substances or to decomposeTo break down into two or more simpler substances.. For example, a chemical property of iron is that it reacts with oxygen and rusts. A chemical property of a substance allows it to undergo a chemical changeThe change of one or more substances into other substances.. A chemical change is the change of one or more substances into another substance. A chemical change is also called a chemical reactionAny chemical change in which at least one new substance is formed..

During some chemical reactions, two or more substances are combined to form one new substance. An example is oxygen combining with iron to form rust. This is called a synthesis reactionA chemical reaction in which two or more substances combine to form a new substance.. During other chemical reactions, one substance is broken down into two or more new substances. An example of this is hydrogen peroxide, which is used to treat small cuts. It breaks down into oxygen and water in the presence of light, which is why hydrogen peroxide is stored in dark bottles. This is called a decomposition reactionA chemical reaction in which one substance is broken down into two or more substances.. A chemical reaction can be very quick, such as paper burning, or very slow, such as food digesting in your stomach.