What is a Chemical Change?

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A substance is considered to go through a chemical change when the molecular structure is modified or changed. It can be changed by mixing two or more substances together, or when energy is added into a particular substance. Either way, the chemical bonds that make up that substance are broken down and regrouped to form a new structure. The new substance that resulted from this process also has new sets of chemical and physical properties compared to the original one.

In simpler terms, a chemical change occurs when a substance is altered at the atomic level to form a new substance. The main difference between a physical change and a chemical change is that the latter is irreversible. For instance, when you crumpled a paper (physical change), you can still straighten it out again and the composition didn’t change. However, when you burned the paper (chemical change), it is not possible to undo the process.

There are four classifications of chemical reactions, namely, the synthesis reaction which happens when at least two simple substances react together and combine to create a third substance that is more complicated; the decomposition reaction, which is the opposite and refers to the breaking down of a complex substance into simpler components; the single-replacement reaction,which refers to the replacement of one element with another one in a complex substance, in order to create a new one; and the double-replacement, which refers to a reaction that involves the exchange of elements between two compounds in order to form new materials.

There are various ways by which one can tell if a chemical change has occurred. Some of the most common ones include observing changes in color and odor. For instance, the changing of the color of the leaves as seasons change signify that a chemical change has occurred. Other examples include the turning of metals into reddish brown as rust forms and the transformation of the flesh of an apple into brown. Changes in odor such as in spoiled milk and rotten eggs are also signs that chemical change has taken place.

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