Types of Chemical Reactions 5 Main Categories + Acid/Base Reactions

Chemical Reactions In a chemical reaction, bonds between compounds are broken and new compounds are formed. In a chemical reaction, elements can also react to form new compounds. Reactants form products

There are 5 main categories of reactions. They all have different characteristics or KEY POINTS to help you recognize them. In addition we will look at acid/base reactions which can also be characterized as double replacement reactions.

Combination Reactions Reactants are forming one product The product is always a SINGLE compound.

Products of Combination Rxns When a metal and a nonmetal react, the product is an ionic compound. EXAMPLE 2K + Cl KCl NOTE: A single compound is the product

Combination Cont. When 2 nonmetals react, more than one combination of product is possible EXAMPLE S (s) + O 2 (g) SO 2 (g) 2S (s) + 3O 2 (g) SO 3 (g) NOTE: A single product is the result of each reaction

Combination Cont. When a transition metal reacts, more than one possible product may result. EXAMPLE Fe (s) + S (s) FeS (s) Iron (II) Sulfide 2Fe (s) + 3S (s) Fe 2 S 3 (s) Iron (III) Sulfide NOTE: Still a single product for each reaction results.

How do you know then? If you are asked to write the products of any reaction where there may be more than one possible product, the name of the product will be given to you. Remember to include Roman Numerals for these transitions metals, (Roman numerals give the charge of the metal)

Decomposition Reactions In decomposition reactions, a single reactant is present. The single reactant breaks down to form other compounds or elements. In effect, it decomposes. A SINGLE REACTANT is present.

Decomposition Reactions A single compound reactant is broken down into two or more products When a single binary compound breaks down, its product will be the constituent elements. EXAMPLE HI H 2 + I 2

Decomposition Cont. If the compound is not binary, the names of the products will be given to you EXAMPLE –CaCO Calcium oxide + carbon dioxide –CaCO CaO + CO 2

Single Replacement Reactions In a single replacement reaction, a single element will replace a similar element in a compound. Na + ZnO Na 2 O + Zn (Na takes the place of Zn) F + NaBr NaF + Br 2 (In this case, the non-metal (F) replaces the non-metal Br- they are similar to each other). A single element is one of the reactants.

Single Replacement Reactions One element replaces another element in the reaction Usually a metal replaces another metal, but single non-metals will replace non- metals in compounds. Not all metals will replace all other metals Whether they will or not is determined by how active they are. –We know for ex. That lithium is a very re-active metal. It will replace any other metal it encounters.

Single Replacement Cont. Whether metals will replace each other and allow the reaction to occur is determined by a chart called the Activity Series of Metals There is one listed.

lithium potassium strontium calcium sodium magnesium aluminum zinc chromium iron cadmium cobalt nickel tin lead HYDROGEN antimony arsenic bismuth copper mercury silver paladium platinum gold Metal Reactivity Chart They are in order of most reactive (lithium) to least reactive (gold)

S-R CONT. The way to use this series is If the single metal reactant is higher on the list than the metal it is replacing in the compound, the reaction will occur. EXAMPLE Mg + Zn(NO 3 ) 2 -- Mg(NO 3 ) 2 + Zn Look at the series and note that Mg is higher on the series than Zn, so the rxn proceeds.

S-R CONT. Look at the next example and predict whether you think the reaction will occur Mg + LiNO HINT- Check the series. Is Mg higher on the list than Li?

S-R CONT The answer is no. Mg is not higher than Li on the list, so the reaction below is a no-go! Mg + LiNO no reaction

S-R CONT. One small rule to keep in mind on the activity series –Metals from Li to Na will replace H from acids and water –Metals from Mg to Pb will replace H from acids only.

Examples with Hydrogen Li + HOH LiOH + H 2 Ca + HNO Ca(NO 3 ) 2 + H 2 Zn + HOH no reaction (Zn wont replace H in water- Zn is below sodium) Zn + HNO Zn(NO 3 ) 2 + H 2 (In this case, Zn will replace H from the acid)

Double Replacement Reactions In these reactions, the positive ions in two ionic compounds, exchange places 2 ionic compounds are the reactants. EXAMPLE –Na 2 S + Cd(NO 3 ) 2 - CdS + 2NaNO 3 Note that Na took the place of Cd and vice versa –Ca(OH) 2 + 2HCl - CaCl 2 + 2H 2 O

Combustion Reactions In these reactions, an element or compound reacts with O 2 (oxygen) often producing energy as heat and light. O 2 is one of the reactants. EXAMPLE 2Mg + O MgO S + O SO 2

Combustion Cont. Many combustion reactions involve a hydrocarbon, a compound made of hydrogen and carbon. Hydrocarbons and O 2 will ALWAYS produce H 2 O and CO 2. If this is the case, the products will always be CO 2 and H 2 O, carbon dioxide and water. EXAMPLE: –2C 6 H O CO 2 + 6H 2 O

Your TURN IDENTIFY THE TYPE OF REACTION BELOW C 6 H 12 O 6 + O CO 2 + 6H 2 O KOH + H 3 PO 4 - K 3 PO 4 + 3H 2 O Mg(ClO 3 ) MgCl 2 + 3O 2 Fe + Pb(NO 3 ) 2 - Fe(NO 3 ) 2 + Pb

IDENTIFY Cl 2 + NaI -- 2NaCl + I 2 H 2 O -- H 2 + O 2 Be + O BeO

FINAL NOTES (for 2day) Remember that there are 7 diatomic molecules –Diatomic molecules are reactive elements that rarely exist alone. So, they form a molecule with themselves H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 This is useful when writing reactions correctly.

EXAMPLE Write the equation: –Potassium reacts with oxygen to produce potassium oxide. –K + O K 2 O People would be tempted to write K + O-- K 2 O and that would be wrong