Types of Chemical Reactions Chemical Reactions A chemical

Types of Chemical Reactions

Chemical Reactions �A chemical reaction has occurred when the starting substances (reactants) recombine to form ending substances (products). �The reactants will, most often, have different chemical and physical properties than the products. �Evidence of a chemical reaction can include (but is not limited to): bubbles, flames, change of color, change of state, precipitate.

Basic Types of Chemical Reactions �Synthesis (or combination) �Decomposition �Single Replacement �Double Replacement �Combustion

Synthesis (Combination) �Just like the name implies, a new substance is formed from two or more reactants. �The typical chemical equation will appear in the form of A + B → AB �A and B can be single elements or molecules. �Example: 2 H 2 + O 2 → 2 H 2 O

Decomposition �Again, as the name implies, this type of reaction involves breaking reactants down into simpler substances. �In many ways, it is the opposite of a synthesis reaction. �The typical chemical equation will appear in the form of AB → A + B �Example: 2 KCl. O 3 → 2 KCl + 3 O 2

Single Replacement �In this type of reaction a single, reactive metal will replace a less reactive metal already bonded in an ionic compound. �The typical chemical will appear as A + BC → B + AC �Example: Cu + 2 Ag. NO 3 → 2 Ag + Cu(NO 3)2 �You will need to use the activity series to determine whether this type of reaction will take place.

Activity Series �The only time a single replacement will take place is when the free metal is more reactive than the metal cation bonded in the ionic compound. �This reactivity is based on ionization energy. A metal with a lower ionization energy is more reactive than one with a higher ionization energy. �You will need to use the activity series to determine which metals are more reactive than others.

Decreasing reactivity Activity Series Name Symbol Lithium Li Potassium K Calcium Ca Sodium Na Magnesium Mg Aluminum Al Zinc Zn Iron Fe Lead Pb (Hydrogen) H Copper Cu Mercury Hg Silver Ag A metal high on the table is more reactive and can replace a metal lower on the table. A metal lower on the table CANNOT replace a metal higher on the table.

Double Replacement Reactions �In this type of reaction, already bonded metal cations basically switch places with one another and bond with the already bonded nonmetal anions. �These reactions usually take place in aqueous solution. �The typical chemical equation will appear as AB + CD → AD + CB �Example: Ca. F 2 + 2 Na. NO 3 → Ca(NO 3)2 + 2 Na. F

Double Replacement Reactions �Usually produce bubbles, a precipitate, or a molecular compound such as water. �In order to occur, one of the following is usually true. ◦ One of the products is only slightly soluble and precipitates. ◦ One of the products is a gas. ◦ One product is a molecular compound such as water.

Predicting Precipitates �When a precipitate is formed, the precipitate can be predicted by using rules of solubility or a solubility table. �Remember, an insoluble substance will not dissolve in water and will therefore precipitate. �In a chemical reaction, a down arrow (↓) is usually written after the formula for the precipitate in order to indicate the precipitate.

Solubility Rules

Acid – Base Double Replacement �An acid, for now, is defined as a substance that produces a hydrogen ion in solution. We will recognize an acid as an ionic compound that starts with H. �Example: HCl, H 2 SO 4 �A base, for now, is defined as a substance that produces a hydroxide ion in solution. We will recognize a base as an ionic compound that ends with – OH. �Example: Na. OH, Ca(OH)2

Acid – Base D. R. Reaction water Ionic salt acid and a base react, in a double replacement reaction, the products formed will be an ionic compound (salt) and water. �Example: 2 Na. OH + H 2 SO 4 → Na 2 SO 4 + 2 H 2 O base �When

Combustion Reaction �In a combustion reaction, a hydrocarbon burns in oxygen. The products formed are always carbon dioxide and water. �The typical format for this reaction is Cx. Hy + O 2 → CO 2 + H 2 O �Example: CH 4 + 2 O 2 → CO 2 + 2 H 2 O

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