There are 5 main chemical reactions known as: combination or synthesis, decomposition, single substitution, double substitution, and combustion. To recognize the type of reaction, you just have to look at the products and reactants of the chemical equation. Knowing the properties of each reaction will help you identify them.
Steps
Method 1 of 6: Identify Combination or Synthesis Reactions
Step 1. Count the number of reagents
As the name implies, a combination or synthesis reaction occurs when 2 or more products combine to form a new product. Remember that the reactants in an equation always go on the left side of the arrow.
Many reactions have only two reagents, but you can have combination reactions with more than two
Step 2. Verify that there is only one final product
As the name of the reaction implies, the reactants must combine to form a new product. All products will be on the right side of the arrow. Rarely, you will find more than one product on the right hand side. However, most equations will only have one product.
- This is an example of a reaction that results in two products: CO2 + H2O C6H12OR6 + O2
Step 3. Practice with some examples
Examples are a great way to learn to recognize specific chemical reactions. The more you review, the more likely you are to remember each type of reaction.
- Example 1: Cu + SO4 COURSE4
- Example 2: CaO + CO2 Thief3
Method 2 of 6: Identify a Decomposition Reaction
Step 1. Count the number of reagents
A decomposition reaction is one in which a reactant degrades or decomposes into its constituent parts. Energy (in the form of light, heat, or electricity) is often the catalyst for the reaction. This type of reaction generates a quantity of products greater than that of reagents. Almost all basic decomposition reactions will have a reagent.
The reagent will be on the left side of the arrow
Step 2. Verify that there are two or more end products
The reagent will decompose into various products. To recognize this type of reaction, just see if the equation looks like the general formula C A + B. Remember that the products are on the right side of the arrow.
This reaction is the opposite of the combination reaction
Step 3. Practice with some examples
It takes practice to be able to identify reactions. The more equations you review, the easier it will be to immediately identify if the reaction is a decomposition.
- Example 1: 2H2O → 2H2 + O2
- Example 2: KClO3 KCl + O2
Method 3 of 6: Identify a Simple Substitution Reaction
Step 1. Identify the general formula for simple substitution
This type of reaction occurs when one element replaces another in a compound. It usually takes the form of AX + Y YX + A or A + XY XA + Y. One reactant will always be a simple element and the other will always be a compound.
- In a simple substitution, the anion (negatively charged ion) or the cation (positively charged ion) will be replaced.
- For example: Cu + AgNO3 Ag + Cu (NO3)2. In this example, copper (Cu) replaces the silver (Ag) cation.
Step 2. Compare the reactant side and the product side
When you review the equation, you can easily determine that a simple substitution has occurred if one of the elements has changed places in the new compound. Use the general formula as a guide to identify the reaction.
- For example: ZnS + O2 ZnO + S
Step 3. Practice with some examples
It takes time and practice to quickly identify a simple substitution reaction. By reviewing various types of examples, you will improve your ability to identify this reaction without looking for information.
- Example 1: Fe + CuSO4 → FeSO4 + Cu. Iron replaces the element copper in the compound.
- Example 2: Fe + HCl FeCl3 + H2. Iron replaces hydrogen.
- Example 3: CaO + Al Al2OR3 + Ca. Aluminum replaces calcium.
Method 4 of 6: Recognize a Double Substitution Reaction
Step 1. Learn the general formula for a double substitution reaction
These reactions are similar to simple substitution, except that both compounds react and there are two substitutions. The general formula is AB + XY AY + XB. The cations and anions of both compounds will recombine to form two new compounds.
- These reactions usually occur between acids and bases, or aqueous metallic compounds.
- For example: KOH + H2SW4 K2SW4 + H2OR.
Step 2. Compare the side of the products and reactants
When you review an equation, you will be able to determine if it is a double substitution reaction because the outer elements will recombine to create a new compound, and the inner elements will recombine to create a new compound. The interior elements will change position because the cation is always written first.
- For example: FeS + HCl FeCl2 + H2S.
- The outer elements, Fe and Cl, will combine to form FeCl2.
- The interior elements, S and H, change position and combine to form H2S.
Step 3. Practice with some examples
Reviewing several examples of double substitution will help you recognize these reactions when you see them on a test. The more examples you review, the more effectively you will identify them.
- Example 1: NaCl + AgNO3 → NaNO3 + AgCl
- Example 2: H2SW4 + 2NaOH → Na2SW4 + 2H2OR
Method 5 of 6: Identify a Combustion Reaction
Step 1. Learn about the components of a combustion reaction
At the most basic level, a combustion reaction is one in which oxygen gas (O2) reacts with something to form carbon dioxide and water. In general, oxygen gas reacts with a compound of carbon and hydrogen. Combustion products are always CO2 and H2OR.
- The generic equation for a combustion reaction is: CxHand + O2 CO2 + H2OR.
Step 2. Verify that the O2 be one of the reactants.
The first step in identifying a combustion is to make sure that gaseous oxygen is one of the reactants. If there is no O2, the reaction will not be a combustion.
- For example: C2H5SH + O2 CO2 + H2O + SO2.
- The O2 It will react with a compound of carbon and hydrogen, so this reaction is probably combustion.
Step 3. Verify that the products generate CO2 and H2OR.
In a combustion reaction, the products almost always contain CO2 and H2O. If the reaction does not produce carbon dioxide and water, it is not combustion.
- For example: C2H5SH + O2 CO2 + H2O + SO2.
- Since CO2 and the H2Or are the products, this reaction is an example of combustion.
Step 4. Practice with some examples
The more problems you solve, the easier it is to identify combustion reactions. With a little practice, you will be able to identify them immediately when you see them.
- Example 1: CH4 + 2O2 CO2 + 2H2OR
- Example 2: C2H5OH + 3O2 2CO2 + 3H2OR
Method 6 of 6: Identify a Reaction by Observation
Step 1. Identify the heat in exothermic reactions
Many synthesis and substitution reactions (single and double) are exothermic, which means they will release heat. Reactions that release a lot of heat (such as termite) can be explosive.
- Take proper safety precautions when working in heat, such as wearing gloves and eye protection.
- The thermite reaction is a simple substitution reaction between iron (III) oxide and aluminum: 3Fe302 + 4Al → 2Al203 + 6Fe
Step 2. See if a precipitation forms
Again, in many synthesis and substitution reactions (single and double), precipitation will form at the bottom of the tube. This consists of any solid material that is not insoluble in water.
Sodium chloride is the white powder that forms when molten sodium burns to form chlorine gas
Step 3. Add heat for endothermic reactions
Most decomposition reactions are endothermic, which means that you have to add heat for them to occur. If heat has to be added, it could be a decomposition reaction.
An example of a decomposition reaction is when mercury (II) oxide decomposes into mercury metal and oxygen gas in the presence of heat: 2 HgO (s) + heat → 2 Hg (l) + O2 (g)
Step 4. Observe if there is light and heat in the combustion reactions
Combustion reactions often explode, forming a large amount of light and heat energy. Often this energy is released as fire. Combustion reactions are always exothermic, which means they release heat.