 Welcome to the video, Common Types of Oxidation Reduction Reactions. There are four common types of oxidation reduction reactions, combination, decomposition, displacement, and combustion. Combination reactions. Combination reactions occur when two reactants combine to form one product. A good example is the reaction of magnesium with air. Two combination reactions actually occurred when the magnesium was ignited in air. Magnesium reacted with both the oxygen and nitrogen gases. These are the two reactions. Which reactant in reaction one is oxidized? Magnesium is oxidized. Its oxidation number changed from zero to plus two. For the reaction with oxygen, the oxidation step is seen below. And this is the reduction step. To balance the equation, the oxidation half reaction is multiplied by two. So that four negative electrons are produced to equal the four negative electrons used in the reduction half reaction. This equation is seen below. And this is the reduction step. Canceling the electrons gives the balanced equation. For the reaction with nitrogen, the oxidation step is the same. And this is the reduction step. To balance the equation, the oxidation half reaction is multiplied by three. So that six negative electrons are produced to equal the six negative electrons used in the reduction half reaction. This equation can be seen below. And this is the reduction step. Then, we combine the ions and cancel the electrons, which gives the balanced equation seen below. Decomposition reactions. Decomposition reactions occur when one reactant decomposes to form two products. A good example is the reaction of mercury-2 oxide to give elemental mercury and oxygen. This reaction can be seen below. Which ion is reduced in this reaction? Mercury-2 plus is reduced. Its oxidation number changed from plus two to zero. This is the reduction half reaction. This is the oxidation half reaction. We multiply the reduction step by two and add the half reactions and cancel the electrons. Displacement reactions. Displacement reactions occur when one element displaces another element from a compound during a chemical reaction. A good example is the reaction of sodium with water. This is the chemical equation for this reaction. Which reactant is oxidized in this reaction? Sodium is oxidized. Its oxidation number changed from zero to plus one. This is the oxidation half reaction. This is the reduction half reaction. We multiply the oxidation step by two and add the balanced half reactions and cancel the electrons. If a larger piece of sodium is added to water, the heat generated from the displacement reaction causes a second reaction to occur. Hydrogen combines with oxygen to form water. The displacement reaction has the same equation as before. This is seen below. This is the combination reaction. This latter reaction occurs in the gas phase and the energy released during the reaction takes the form of heat and light. It produces a flame. Combustion reactions. Combustion reactions occur when a substance reacts with oxygen, usually with the rapid generation of heat to produce a flame. A good example is the reaction of hydrogen with oxygen seen below. Which molecule is reduced in this reaction? Oxygen is reduced. The oxidation number of oxygen changed from zero to minus two. Now, you will have an opportunity to test your knowledge by classifying the following reactions. For each one, determine if it is a combination, decomposition, displacement, or combustion reaction. Feel free to pause the video at any point if you need more time. How would you classify this reaction? This is a combination reaction because there are two reactants combining to form one product. How would you classify this reaction? This is a decomposition reaction. Displacement reactions happen when one element displaces another element from a compound during a chemical reaction. Congratulations! You have completed this video. Common types of oxidation reduction reactions.