Chemical changes are fundamental changes that produce new combinations of matter. A distinction is made between chemical and physical changes. The signs of chemical changes are discussed, and several types of chemical changes are explored in this lesson.
Definition of Chemical Change
Think of what cookies look like before baking and after baking. The raw cookie dough looks and tastes very different when compared to the finished cookie. Is this an example of a physical change or a chemical change? The answer is a chemical change, but how do you know?
Before a discussion of chemical changes can occur, a distinction needs to be made regarding physical changes. Physical changes result from a changing in the physical state of a substance. The physical change can be melting, evaporation, or boiling. For instance, ice melts into liquid water, and the liquid water can be turned into steam through boiling. The arrangement of the molecules making up the ice and water change into different states, but the molecules still remain water molecules during each change.
A chemical change occurs as the result of a chemical reaction. During a chemical reaction, the atoms within a substance are rearranged into different combinations. For example, sugar undergoes a chemical change when it is cooked to make caramel. The heat from the cooking converts sugar molecules into different molecules that give caramel its color and flavor.
Types of Chemical Changes
Although many thousands of different chemical reactions exist, many of them have similar characteristics. These similarities allow us to begin classifying the different chemical changes into broad types.
Combination happens when two or more substances combine together in a chemical reaction to form one or more different substances. Combination reactions can result in the corrosion of metals, like iron with oxygen from the air. Combustion reactions, such as a burning candle, are also examples of the chemical change through the combination of wax and oxygen in a reaction that produces heat, light, and carbon dioxide.
Decomposition, the opposite of combination, occurs when a single substance breaks down into two or more different substances. This type of chemical change is evident when fruit decomposes over time. Decomposition can also occur when substances absorb energy, such as the decomposition of water into hydrogen and oxygen with electricity.