Types of Reactions

5 Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B Combustion reaction (of a hydrocarbon) CxHy + O2  CO2 + H2O + energy ASingle-replacement reaction A + BC  AC + B Objective: To classify a chemical reaction as one of the following types: combination (synthesis), decomposition, single replacement, double replacement, or neutralization. BDouble-replacement reaction AB + CD  AD + CB Ause activity series to predict B use solubility chart to predict

Synthesis Reactions General Formula: A + B  AB A is an element (identifying characteristic: only ONE product!) A is an element B is an element AB is a compound Hints!! Don’t forget the formulas for diatomic elements, aka the “7-ups” Always write the correct formula for the compound based on the charges of the ions BEFORE balancing!

Synthesis Reaction Na(s) + Cl2(g)  NaCl Na(s) + Cl2(g)  NaCl (s) Example: Sodium + chlorine 1. Write the formulas for the reactant elements, including states of matter 2. Write the correct formula for the product compound based on the charge of the ions (remember that ionic compounds are solid at room temperature unless they are dissolved in water). Na1+ Cl1- 3. Balance the equation Na(s) + Cl2(g)  NaCl 2 Na(s) + Cl2(g)  NaCl (s) 2

Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2  2 NaCl Na Cl Na+ Cl - Cl Cl - Na+ Na General form: A + B  AB element element compound

Try this one! Potassium + oxygen

The answer is….. 4 K(s) + O2 (g) 2 K2O (s) Write the ions K1+ O2- K O CrissCross the charges K2O Reduce if needed, ignore “1”

Decomposition Reactions General formula: AB  A + B Identifying characteristic: only ONE reactant! AB is a compound A is an element B is an element

Decomposition Reaction Ex: decomposition of water Write the formula of the reactant compound 2. Write the formulas of the element products 3. Balance the equation 2 H2O(l) 2 H2(g) + O2(g)

Decomposition Reaction 2 H2O(l) 2 H2 (g) + O2 (g) H O H H O H + O H O H H H General form: AB A + B compound two or more elements or compounds

Try this one! The decomposition of iron(III) oxide (HINT: the roman numeral tells you the charge of the iron!) 2 Fe2O3(s) 4 Fe(s) + 3 O2(g)

Combustion Reactions CxHy + O2  CO2 + H2O + energy A hydrocarbon* Identifying characteristic: hydrocarbon and oxygen A hydrocarbon is a molecule that consists of carbon and hydrogen

Tips on Balancing Combustion Reactions Do an Atom Inventory 1st, balance the carbons 2nd, balance the hydrogens 3rd, balance the oxygens If the oxygens don’t balance with a whole number, balance with a ½ number, THEN multiply all coefficients by 2.

Combustion of a Hydrocarbon Many homes get heat from propane (C3H8) heaters. Write a balanced chemical equation for the complete combustion of propane gas.

C3H8(g) + O2(g)  CO2(g) + H2O(g) + energy 5 3 4 1 / 3 / 8 H 2 8 10 2 / O / 10 / 3 7 Do an Atom Inventory 1st Balance Carbons 2nd Balance hydrogens 3rd Balance oxygens

Combustion of Methane Gas + One methane molecule Two oxygen molecules One carbon dioxide molecule Two water molecules Heat and flame CH4 + 2 O2 CO2 + 2H2O + energy 1 carbon + 4 hydrogen 1 carbon + 2 oxygen 2 oxygen + 4 hydrogen 4 oxygen Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 245

Try this one! Write the complete combustion equation for butane gas (formula for butane is C4H10). Butane is the gas found in lighters.

The answer is……. 2 C4H10 + 13 O2 8 CO2 + 10 H2O + energy 4 5 6.5 2 13 1. Balance C: C4H10 + O2 CO2 + H2O + energy 2. Balance H: C4H10 + O2 4 CO2 + H2O + energy 5 3. Balance O: C4H10 + O2 4 CO2 + 5 H2O + energy 6.5 (hint: need to use a ½) 4. Double all coefficients: 2 13 C4H10 + O2 CO2 + H2O + energy 8 10

Single Replacement Reactions General Formula: A + BC  B + AC Identifying characteristic: reactants are an ELEMENT and a COMPOUND A is an element BC is a compound A and B switch places to form: B (an element) and AC (a compound) Need to use an Activity Series to determine if a reaction will occur

Single Replacement Reactions Mg + CuSO4  MgSO4 + Cu General form: A + BC  AC + B How do you know if Mg switches places with the Cu or the SO4? If the element A forms a cation, it replaces the cation in the compound BC If the element A forms an anion, it replaces the anion in the compound BC

Help, I need a review!! Ionic Compounds are ALWAYS What is a cation and an anion? An anion is a “-” charged ion A cation is a “+” charged ion Ionic Compounds are ALWAYS written cation then anion!! Ex: MgCl2 Mg2+ Cl1-

Activity Series: Will a reaction occur ? The cation list Al(s) + CuSO4 (aq) Element Reactivity The anion list Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Al (the element) is higher on the chart than Cu (in the compound) Halogen Reactivity F2 Cl2 Br2 I2 Al Al is STRONGER so overtakes/ replaces Cu in the compound and Kicks Cu out by itself! Al Foiled again! Aluminum beats Copper! Cu Cu

Aluminum vs copper II sulfate 2 Al (s) + CuSO4 (aq) 3 Cu 3 + Al2(SO4)3(aq) (s) Al is higher on the chart than Cu, so it kicks Cu out of the compound. Al then makes a compound with SO4 Al3+ SO42- 3 2 Al (SO4) Now, balance the equation.

Your turn! Will a reaction occur? Yes or No Element Reactivity Will a reaction occur? Yes or No If “Yes”, write a complete balanced equation Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Halogens F2 Cl2 Br2 I2 NaNO3(aq) + Ag(s) ?? F2(g) + NaI(aq) ??

The Answers… NaNO3(aq) + Ag(s) NR (abbrev for no reaction) Why? Because Ag (the element) is NOT higher on the chart than Na F2(g) + 2 NaI(aq) 2 NaF(aq) + I2(g) Why? Because F2 IS higher on the chart than I2 Since F2 becomes the F- anion, it replaces the anion in NaI

Potassium reacts with Water P O W ! * 2 HOH * Often times it helps to think of water as HOH

Double Replacement Reactions AB + CD  CB + AD Identifying characteristic: Both reactants are ionic compounds Watch how the cations switch places! A reaction ONLY occurs if at least ONE of the products is a solid (or H2O). A solubility chart is needed to determine if the products are solids or remain dissolved (aqueous).

Will Al(NO3)3 dissolve in water Will barium phosphate dissolve in water? Will PbI2 dissolve in water? Yes No

Double Replacement Reactions Will a reaction occur? K2CO3(aq) + BaCl2(aq) BaCO3 + KCl 2 (s) (aq) 1. Determine the two products based on the charge of the ions Using the solubility chart, determine if each product is a. Aqueous (which means it is soluble in water) b. Solid (which means it is insoluble in water) If one of the products is a solid, the reaction occurs, so BALANCE it If BOTH products are aqueous, then NO REACTION occurs. Cross out products and write “NR”

Double Replacement Reaction

Double Replacement Practice NR NaCl (aq) + KNO 3(aq) NaNO3(aq) + KCl (aq) (NH4)2CO3(aq) + 2 HOH(l) H2CO3(aq) + NH4(OH)(aq) AgNO3(aq) + KCl(aq)

Formation of a solid AgCl AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s)