Chapter 8 Chemical Equations

Parts of a Chemical Equation O2(g) + Fe(s)  Fe2O3(s) Products – chemicals produced in a chemical reaction. (products) Reactants – chemicals reacted together in a chemical reaction. Products = Fe2O3 Reactants = O2 and Fe  - yields or produces

Parts of a Chemical Equation O2(g) + Fe(s)  Fe2O3(s) (g) = gas (s) = solid (l) = liquid examples: water, Hg, Br2, organics (aq) = aqueous A homogeneous solution. Most of what we use in class

Parts of a Chemical Equation O2(g) + Fe(s)  Fe2O3(s) Why O2 not O and why Fe not Fe2? Oxygen is diatomic. Meaning that in order to be at its lowest energy, oxygen will bond with other oxygen. Diatomic Elements – H, N, O, F, Cl, Br, I and probably (At) Trivial others: S8 and P4

Let’s Sing There are seven Diatomic Elements That you must know. (repeat) Fluorine, Chlorine Bromine, Iodine Nitrogen, Oxygen Hydrogen

Other Symbols Things on the reaction arrow Catalyst – speeds up a reaction. Inhibitor – slows down a reaction Neither are parts of the products or reactants. Energy – in the form of heat, light or electricity. Probably heat! NH4Cl Δ

Example 1 When solid mercury (II) sulfide is heated with oxygen, liquid mercury metal and gaseous sulfur dioxide are produced.

Example 2 Oxygen gas can be made by heating potassium chlorate in the presence of the catalyst manganese dioxide. Potassium chloride is left as a solid residue.

Balancing Equations Balanced Equation – an equation that has the same number and type of atoms on the product and reactant sides. We balance equations by putting in coefficients. A coefficient is a multiplier. You MAY NOT change subscripts, unless they are yours and you made a mistake initially when you wrote the equation.

Why do we balance equations? Law of conservation of matter – matter is neither created nor destroyed.

Example 3   Δ KClO3  O2 + KCl K Cl O

Example 4 Al + O2  Al2O3 Al O

Example 5 AgNO3 + Cu  Cu(NO3)2 + Ag Ag N O Cu

Example 5 (again) AgNO3 + Cu  Cu(NO3)2 + Ag Ag NO3 Cu

General Hints In general you will want of get rid of odd numbers. Also, work with combined elements before working on lone elements.

Types of Reactions Chapter 8

Five Common Types of Reactions Synthesis (Direct combination or combination) Decomposition Single Replacement (Single Displacement) Double Replacement (Double Displacement) Combustion

Synthesis Two or more elements or compounds combine to form a new compound. General Form: A + B  AB

Specific Examples Cl2 + Al 

Specific Examples Sr + N2 

Decomposition A compound breaks down into two or more elements and/or compounds. General Form: AB  A + B

Specific Examples MgO 

Specific Examples CoBr3 

Specific Examples Carbonates break down into their metal oxide and carbon dioxide. Na2CO3 

Specific Examples Hydroxides break down into their metal oxide and water. NaOH 

Single Replacement An element replaces another element inside a compound. General Form: A + BC  B + AC or A + BC  C + BA

Activity Series of Metals An activity series of metals needs to be consulted to determine if a reaction will take place or not. A more reactive metal will replace a less reactive metal in a compound. Less commonly, there is also an activity series of non-metals as well.

Activity Series of Metals Lithium Most Reactive Potassium Barium Calcium Sodium Magnesium Aluminum Zinc Iron Nickel Tin Lead Hydrogen Copper Mercury Silver Gold Least Reactive

Activity Series of Halogens Fluorine Most Reactive Chlorine Bromine Iodine Least Reactive

Specific Examples Au + NaCl 

Specific Examples Cu + AgNO3 

Specific Examples Li + H2O 

Specific Examples Al + Mg(NO3)2 

Double Replacement One element out of a compound replaces another element out of a compound. General Form AB + CD  AD + CB

How do I know a reaction will occur? That is a topic for our next section, for this chapter we will assume they all work. Live the LIE!

Evidence of a Double Replacement Reaction A precipitate forms. Insoluble solid A gas is produced. Water is produced.

Specific Examples KCl + AgNO3 

Specific Examples HCl + NaOH 

Specific Examples Na2CO3 + Cd(NO3)2 

Specific Examples AlPO4 + Zn(ClO2)2 

Specific Examples HBr + K2CO3

“Tooth Fairies” NH4OH = NH3 + H2O H2CO3 = H2O + CO2

Combustion A hydrocarbon reacts with oxygen to produce carbon dioxide and water. Heat and light are also produced. General Form: CxHyOz + O2  CO2 + H2O

Specific Examples Combusting propane (C5H12) C5H12 + O2  CO2 + H2O

Specific Examples Combusting sugar (C12H22O11) C12H22O11 + O2  CO2 + H2O

Specific Examples Tricky Balancing CH5 + 