Summary of the Main Reaction Types

In combination reactions, the reactants combine to form a single product. Because a combination of an element and a compound or two compounds would be difficult to classify as a combination reaction, the reactions on the AP test that are combination reactions tend to use two elements. So, if you encounter two elements on the test, they will undergo a combination reaction. 

Sample Magnesium metal is heated strongly in the presence of nitrogen gas. 

Answer When you read this, you have to know that nitrogen gas is a diatomic element. You also have to assume that strong heat means the reactants probably wouldn t react otherwise. When you write the reactants and products, you do not need to write the states of conditions of the reaction  

The formula Mg3N2 was obtained by using the crisscross method. You can use the periodic table on this part of the test, so you should really make an effort to memorize the common charges of ions, or oxidation states, by an elements position on the chart. 

These are probably the easiest to detect, even if they aren t the easiest to determine the products for. The reason they are easiest to detect is there will only be a single reactant. You will usually be told something is being done to it, like heating, but no other reactant is mentioned. There may be a catalyst mentioned, but it will be labeled as a catalyst. 

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