Chemical Reactions

Writing Formulas: Review carbon tetrafluorideCF 4 Na 3 PO 4 sodium phosphate Cu 2 SO 4 cuprous sulfate AnalysisIf “Yes” The compound is covalent: the prefixes give the subscripts. * Are there prefixes present The compound is ionic: subscripts must be determined by balancing charges prefixes  covalent  prefixes indicate subscripts metal  ionic  balance charges  3 Na 1+ needed for 1 PO 4 3- metal present  ionic  balance charges  2 Cu 1+ needed for 1 SO 4 2- Al 2 S 3 aluminum sulfide metal present  ionic  balance charges  2 Al 3+ needed for 3 S 2- N 2 O 5 dinitrogen pentoxide prefixes  covalent  prefixes indicate subscripts NH 4 NO 3 ammonium nitrate polyatomic ion present  ionic  balance charges  1 NH 4 1+ needed for 1 NO 3 1- PbO 2 plumbic oxide metal present  ionic  balance charges  1 Pb 4+ needed for 2 O 2- Fe 2 (CO 3 ) 3 ferric carbonate metal present  ionic  balance charges  2 Fe 3+ needed for 3 CO 3 2-

Indicators of a Chemical Change Precipitate Color Change Gas Given off Temperature Change Light Produced

In a chemical reaction, reactants are chemically combined In a chemical reaction, reactants are chemically combined or broken down to make (produce) products. arrow always points toward products! arrow always points toward products! CH 4(g) + 2O 2(g) CO 2(g) + 2H 2 O (l) CH 4(g) + 2O 2(g) CO 2(g) + 2H 2 O (l) reactants products Reactants vs. Products (s)solid (l)liquid (g)gas (aq) aqueous (dissolved in water) yields

- a whole number that is placed before a symbol of an element or formula of a compound in order to balance a chemical equation. A coefficient multiplies the entire formula by that whole number. - a whole number that is placed before a symbol of an element or formula of a compound in order to balance a chemical equation. A coefficient multiplies the entire formula by that whole number. Example - 2 Al + 6 HCl  2 AlCl H 2 Example - 2 Al + 6 HCl  2 AlCl H 2 2 Al  2Al 2 Al  2Al 6H  6H 6H  6H 6Cl  6Cl 6Cl  6Cl Coefficient

Diatomic Elements - there are seven elements that exist as diatomic molecules in which two atoms of the same element bond together. - there are seven elements that exist as diatomic molecules in which two atoms of the same element bond together. Br I N Cl H O F Br I N Cl H O F Whenever these elements appear as free elements (by themselves) in a chemical equation, they MUST have a subscript "2" written beside them. Whenever these elements appear as free elements (by themselves) in a chemical equation, they MUST have a subscript "2" written beside them. Example H 2 + O 2  2H 2 O Example H 2 + O 2  2H 2 O Example Na + Cl 2  2NaCl Example Na + Cl 2  2NaCl Example H 2 + N 2  2NH 3 Example H 2 + N 2  2NH 3

Writing Chemical Equations Sometimes chemical equations are written using the names of the free elements and compounds. But, usually chemical equations are written with symbols for free elements and formulas for compounds instead of names. Sometimes chemical equations are written using the names of the free elements and compounds. But, usually chemical equations are written with symbols for free elements and formulas for compounds instead of names. Examples: Examples: magnesium + hydrochloric acid  magnesium chloride + hydrogen magnesium + hydrochloric acid  magnesium chloride + hydrogen Mg + 2 HCl  MgCl 2 + H 2 Mg + 2 HCl  MgCl 2 + H 2 sodium + water  sodium hydroxide + hydrogen sodium + water  sodium hydroxide + hydrogen 2Na+ 2H 2 O  2 NaOH + H 2 2Na+ 2H 2 O  2 NaOH + H 2

There are five different types of reactions… There are five different types of reactions… 1. SYNTHESIS or COMBINATION… 1. SYNTHESIS or COMBINATION… - two or more reactants combine to produce one product. - two or more reactants combine to produce one product. Ex… Ex… Mg (s) + O 2 (g) MgO (s) Mg (s) + O 2 (g) MgO (s) CaO (s) + CO 2 (g) CaCO 3 (s) CaO (s) + CO 2 (g) CaCO 3 (s) KNO 2 (s) + O 2 (g) KNO 3 (s) KNO 2 (s) + O 2 (g) KNO 3 (s) 2 2 2:1 2 1:1 1 2: Types of Reactions

2. DECOMPOSITION… 2. DECOMPOSITION… - opposite of synthesis - opposite of synthesis - A single compound (one) reactant breaks down (decomposes) into two or more elements or new compounds (products). - A single compound (one) reactant breaks down (decomposes) into two or more elements or new compounds (products). Ex… Ex… HgO Hg + O 2 HgO Hg + O :1 HNO 3 N 2 O 5 + H 2 O HNO 3 N 2 O 5 + H 2 O 2 2 1:1 Types of Reactions

3. SINGLE DISPLACEMENT… 3. SINGLE DISPLACEMENT… - one element in a compound is displaced (kicked out) by another - one element in a compound is displaced (kicked out) by another (more reactive) element. Ex… Ex… Mg + Zn(NO 3 ) 2 Mg + Zn(NO 3 ) 2 Mg(NO 3 ) 2 + Zn 1:1 1:1 Cl 2 + KI Cl 2 + KI KCl + I :2 2:1 ** metals can only replace metals and vice versa for non-metals! ** metals can only replace metals and vice versa for non-metals! - reactants =1element &1compound …products = 1element & - reactants =1element &1compound …products = 1element & 1compound. -By definition, all single replacement reactions are redox reactions - By definition, all single replacement reactions are redox reactions Types of Reactions

4. DOUBLE DISPLACEMENT… 4. DOUBLE DISPLACEMENT… - cations of two different compounds trade places. - cations of two different compounds trade places. - reactants = 2 compounds …products = 2 different compounds - reactants = 2 compounds …products = 2 different compounds Ex… Ex… NaCl + AgNO 3 NaCl + AgNO 3 AgCl + NaNO 3 1:1 1:1 Ca(OH) 2 + H 3 PO 4 Ca(OH) 2 + H 3 PO 4 H(OH) + Ca 3 (PO 4 ) 2 H(OH) + Ca 3 (PO 4 ) 2 (H 2 O) :2 6:1 Types of Reactions

5. COMBUSTION… 5. COMBUSTION… - generally involves the burning of a hydrocarbon. - generally involves the burning of a hydrocarbon. - fires generally need oxygen to burn (reactant). - fires generally need oxygen to burn (reactant). - fires generally release water and carbon dioxide (prod). - fires generally release water and carbon dioxide (prod). - reactants = hydrocarbon and O 2 …products = H 2 O and CO 2 - reactants = hydrocarbon and O 2 …products = H 2 O and CO 2 C 3 H 8 + O 2 CO 2 + H 2 O C 3 H 8 + O 2 CO 2 + H 2 O :5 3:4 Ex… Ex… C 6 H 12 O 6 + O 2 CO 2 + H 2 O C 6 H 12 O 6 + O 2 CO 2 + H 2 O :6 6:6 - oxygen combines with a substance and releases energy in the form of heat and light. - oxygen combines with a substance and releases energy in the form of heat and light. Types of Reactions

identify the following types of rxns… identify the following types of rxns… Pb(NO 3 ) 2 + K 2 CrO 4 Pb(NO 3 ) 2 + K 2 CrO 4 PbCrO 4 + 2KNO 3 double displacement double displacement 2Al(OH) 3 2Al(OH) 3 Al 2 O 3 + 3H 2 O decomposition decomposition CH 4 + 2O 2 CH 4 + 2O 2 CO 2 + 2H 2 O combustion combustion 4Li + O 2 4Li + O 2 2Li 2 O synthesis synthesis 2Al + 3CuSO 4 2Al + 3CuSO 4 Al 2 (SO 4 ) 3 + 3Cu single displacement single displacement Types of Reactions

Balancing Chemical Equations

Balancing Equations chemical equations need to be balanced to comply w/ the chemical equations need to be balanced to comply w/ the Law of Conservation of Mass. (matter cannot be created or destroyed) # of atoms for each element must = each other on both sides of rxn. # of atoms for each element must = each other on both sides of rxn. ** use coefficients to balance. ** use coefficients to balance. - must be whole #s - must be whole #s - large # in front of compound - large # in front of compound - indicate the mole ratio each time you balance! - indicate the mole ratio each time you balance! start from far left and work your way to the right! start from far left and work your way to the right!

O 2 (g) + H 2 (g) H 2 O (l) O 2 (g) + H 2 (g) H 2 O (l) Practice… Practice… O atoms 1 O atom 4 H atoms Mole Ratio = 1:2 2 Fe (s) + O 2 (g) Fe 2 O 3 (s) Fe (s) + O 2 (g) Fe 2 O 3 (s) Mole Ratio = 4:3 2 Balancing Equations

Practice… Practice… H 2 O 2 (aq) O 2 (g) + H 2 O (l) H 2 O 2 (aq) O 2 (g) + H 2 O (l)2 2 Mole Ratio = 2 1:2 AgNO 3 + H 2 S Ag 2 S + HNO 3 AgNO 3 + H 2 S Ag 2 S + HNO Mole Ratio = 2:1 1:2 ** balance polyatomics together! MnO 2 + HCl MnCl 2 + H 2 O + Cl 2 MnO 2 + HCl MnCl 2 + H 2 O + Cl Mole Ratio = 1:4 1:2:1 Balancing Equations