Chemical reactions take place when one set of chemical substances transforms into new ones with different chemical identities. You might observe physical effects, such as light or heat, which might indicate a chemical reaction is occurring. Chemical reactions follow a specific formula, so you can label each reaction as one of six types -- synthesis, combustion, decomposition, single replacement, double displacement or acid-base.
Define each type of chemical reaction. In a synthesis reaction, two or more chemical substances combine to form a new compound, so the formula looks like A + B = AB. Decomposition is like the opposite of synthesis -- a compound breaks down into two or more components. Combustion reactions are rapid oxidation reactions that produce heat and light; they typically occur when a substance reacts with oxygen to form an oxide, but can occur with other oxidants. Single-replacement reactions, also called substitution, occur when one element trades places with another in a compound. Similarly, double-displacement reactions transpire when the anions and cations of two molecules switch places and form two new compounds. Acid-base reactions, also called neutralization, are specific double-displacement reactions in which an acid reacts with a base.
Make a list of any “giveaways” that a particular type of reaction occurs. For example, if you see oxygen is a reactant along with a hydrocarbon, and water and carbon dioxide are two products of a reaction, then it is probably a combustion reaction. Double-displacement reactions tend to involve ionic solutions that produce ionic compounds, one of which forms a precipitate; if you notice a precipitate in your reaction, you know it can likely be a double displacement reaction.
Look at the formula for a chemical reaction and ask yourself a series of questions. Do you see any of the “giveaways” you listed? Does the reaction involve two or more chemicals to make one compound? If so, then it’s a synthesis reaction. Does your reaction follow the formula AB + CD react to form AD + CB? If so, it’s a double-displacement reaction.
- Make a chart with the name of each reaction followed by the formula of reactants and products. Consider adding examples or notes about the reactants or products. If you have difficulty identifying the reaction, refer to your chart to determine which pattern the reaction follows.
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