Types of Reactions Involving a Chemical Change

Synthesis Reactions

• A synthesis chemical reaction is one where two or more simple elements come together to form a more complex compound. The chemical equation for this type of reaction is A + B ' AB. An example of a synthesis reaction is the combining of iron and sulfur to form iron sulfide. A synthesis reaction also occurs during the formation of potassium chloride from potassium and chlorine gas.

Decomposition Reactions

• A decomposition chemical reaction can be thought of as the inversion of synthesis. Decomposition occurs when a complex substance is broken down into its basic, more simpler parts. The chemical equation for decomposition is depicted as AB ' A + B. A great example of decomposition is when oxygen and hydrogen gas is formed during the electrolysis of water. Another example is when carbonates decompose into oxides and carbon dioxide.

Single Replacement Reactions

• During a single replacement reaction, a single, uncombined element takes the place of another element within a compound. The chemical equation is A + BC ' AC + B. A perfect example of a single displacement reaction is where magnesium hydroxide and hydrogen gas is formed whenever magnesium replaces hydrogen in water.

Double Replacement Reactions

• During a double replacement reaction, a reactive element in each of two compounds switch to form two entirely new compounds. The chemical equation would be AB + CD ' AC + BD. An example of the double replacement reaction is when silver nitrate mixes with sodium chloride to form silver chloride and sodium nitrate.

The Role Of Energy During Chemical Reactions

• No discussion regarding chemical reactions would be complete without mentioning the role of energy. Energy is neither created or destroyed. What actually happens is that energy is either absorbed or released during these chemical reactions. A reaction in which energy is absorbed is called an endothermic reaction. These types of reactions must have energy to occur. Most of the time, it is either heat energy or electrical energy that is absorbed. A reaction in which energy is released is called an exothermic reaction. These types of reactions typically release heat that was stored within the chemical bonds of the reactants.