Chemical Reactions

Quick Review massvolume Matter is the “stuff” that makes up the universe. All matter has ______ and ________. All matter is composed of basic building blocks known as _______. atoms

Quick Review We know that matter can undergo changes both _________ and __________. physical chemical

Quick Review When matter undergoes a chemical change or reaction the composition of the substance is changed and chemical bonds are formed. When matter undergoes a physical change the composition of the substance is unchanged.

What happens during a chemical reaction? Atoms in the reactants are rearranged to form one or more different substances (products). Atoms in the reactants are rearranged to form one or more different substances (products). Old bonds are broken; new bonds form. Old bonds are broken; new bonds form. Reactants Products Reactants Products MgO + C CO + Mg MgO + C CO + Mg

How do you know a chemical reaction has occurred? Evolution of heat and light Evolution of heat and light Formation of a gas Formation of a gas Formation of a precipitate (formation of a solid in a solution) Formation of a precipitate (formation of a solid in a solution) Color change Color change Temperature changes (endothermic/exothermic) Temperature changes (endothermic/exothermic) A new odor is produced A new odor is produced

Learning Check 1 Classify each of the following as a Classify each of the following as a 1) physical change or 2) chemical change 1) physical change or 2) chemical change A. ____ a burning candle B. ____ melting ice C. ____ toasting a marshmallow C. ____ toasting a marshmallow D. ____ cutting a pizza D. ____ cutting a pizza E. ____ polishing silver E. ____ polishing silver

Solution 1 Classify each of the following as a Classify each of the following as a 1) physical change or 2) chemical change 1) physical change or 2) chemical change A. __2__ a burning candle B. __1_ melting ice C. __2__ toasting a marshmallow C. __2__ toasting a marshmallow D. __1__ cutting a pizza D. __1__ cutting a pizza E. __2__ polishing silver E. __2__ polishing silver

A Chemical Reaction Reactants Products Reactants Products

Learning Check 2 A. How does an equation indicate a change in the identity of the reacting substances? the identity of the reacting substances? B. How did the black and white reactants combine? combine? C. Did all the reactants form product? Why or why not? why not?

Solution 2 A. How does an equation indicate a change in the identity of the reacting substances? the reacting substances? The formulas of the reactants are different than the formulas of the products. B. How did the black and white reactants combine? 1 black combined with 1 white. 1 black combined with 1 white. C. Did all the reactants form product? Why or why not? No. There were more black reactants than white. No. There were more black reactants than white.

How do we represent these chemical reactions? Chemists use statements called equations. Chemists use statements called equations. Chemical equations do not express numerical equalities as in math. Chemical equations do not express numerical equalities as in math. Chemical equations show the direction in which the reaction progresses. Instead of an equal sign (=), an arrow is used Chemical equations show the direction in which the reaction progresses. Instead of an equal sign (=), an arrow is used (means yield) (means yield)

Word Equations A statement using words to describe a chemical reaction. A statement using words to describe a chemical reaction. Sodium (s) + Chlorine (g) Sodium Chloride (s) The statement reads sodium and chlorine react to produce or yield sodium chloride. Useful but lacks important information Useful but lacks important information

Chemical Symbols Chemical Symbols

Skeletal Equation Uses chemical formulas instead of words to identify reactants and products. Uses chemical formulas instead of words to identify reactants and products. Important step in writing a complete equation Important step in writing a complete equation Na (s) + Cl 2 (g) NaCl (s) Na (s) + Cl 2 (g) NaCl (s)

Learning Check 4 Write skeleton equations for the following word equations. Write skeleton equations for the following word equations. hydrogen(g) + bromine(g) hydrogen bromide(g) carbon(s) + sulfur(s) carbon disulfide(s)

Solution 4 Write skeleton equations for the following word equations. Write skeleton equations for the following word equations. hydrogen(g) + bromine(g) hydrogen bromide(g) H 2 (g) + Br 2 (g)HBr(g) carbon(s) + sulfur(s) carbon disulfide(s) C(s) + S(s) CS 2 (s)

Writing a Chemical Equation Chemical symbols give a “before-and- after” picture of a chemical reaction Chemical symbols give a “before-and- after” picture of a chemical reaction ReactantsProducts ReactantsProducts MgO + CCO + Mg MgO + CCO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium

Types of Reactions There are six types of chemical reactions we will talk about: Synthesis reactions Decomposition reactions Single displacement reactions Double displacement reactions Combustion reactions You need to be able to identify the type of reaction

1. Synthesis reactions Synthesis reactions occur when two substances (generally elements) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant  1 product Basically: A + B  AB Example: 2H 2 + O 2  2H 2 O Example: C + O 2  CO 2

Synthesis Reactions Here is another example of a synthesis reaction

2. Decomposition Reactions Decomposition reactions occur when a compound breaks up into the elements or in a few to simpler compounds 1 Reactant  Product + Product In general: AB  A + B Example: 2 H 2 O  2H 2 + O 2 Example: 2 HgO  2Hg + O 2

Decomposition Reactions Another view of a decomposition reaction:

3. Single Replacement Reactions Single Replacement Reactions occur when one element replaces another in a compound. A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). element + compound  product + product A + BC  AC + B (if A is a metal) OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!)

Single Replacement Reactions Another view:

Single Replacement Reactions Sodium chloride solid reacts with fluorine gas NaCl (s) + F 2(g)  NaF (s) + Cl 2(g) Note that fluorine replaces chlorine in the compound Aluminum metal reacts with aqueous copper (II) nitrate Al (s) + Cu(NO 3 ) 2(aq)  Cu (s) + Al(NO 3 ) 3(aq)

4. Double Replacement Reactions Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound Compound + compound  product + product AB + CD  AD + CB

Double Replacement Reactions Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together Example: AgNO 3(aq) + NaCl (s)  AgCl (s) + NaNO 3(aq) Another example: K 2 SO 4(aq) + Ba(NO 3 ) 2(aq)  KNO 3(aq) + BaSO 4(s) 2

5. Combustion Reactions Combustion reactions occur when a hydrocarbon reacts with oxygen gas. This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”: 1) A Fuel (hydrocarbon) 2) Oxygen to burn it with 3) Something to ignite the reaction (spark)

Combustion Reactions In general: C x H y + O 2  CO 2 + H 2 O Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by- products like carbon monoxide) Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C 8 H 18 )

Combustion Example C 5 H 12 + O 2  CO 2 + H 2 O Write the products and balance the following combustion reaction: C 10 H 22 + O 2  CO 2 + H 2 O

6. Acid-base This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water: This is a special kind of double displacement reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water: HA + BOH ---> H2O + BA HA + BOH ---> H2O + BA One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide: One example of an acid-base reaction is the reaction of hydrobromic acid (HBr) with sodium hydroxide: HBr + NaOH ---> NaBr + H2O HBr + NaOH ---> NaBr + H2O

Mixed Practice State the type and balance the following reactions: BaCl 2 + H 2 SO 4  C 6 H 12 + O 2  Zn + CuSO 4  Cs + Br 2  FeCO 3  BaSO 4 + HCl2 CO 2 + H 2 O 66 9 ZnSO 4 + Cu CsBr22 FeO + CO 2