6 2H2 + O2 → 2H2O Parts of a chemical reaction: ReactantsProductsYieldSignReactants – substances that are reacting; the starting substancesProducts – new substances that are made; substances formed during reaction
7 Physical states of compounds are often given in a chemical equation.
8 Conservation of Mass- During a chemical reaction, mass is not created or destroyed.– Mass is conserved!-All atoms present in the reactants must be present in the products.-Same number of each type atom on both sides of arrowreactantsproducts
9 The equation is balanced! Balancing Chemical Equations- The number of atoms of each element must be the same on both sides of the yield sign.2H2 + O2 → 2H2O4 Hydrogen2 Oxygen4 Hydrogen2 OxygenThe equation is balanced!
10 When balancing an equation, you can only change the coefficient before the compound. Never change the subscript!2Ca(NO3)2coefficientsubscript
11 Multiply the coefficient by any subscripts to determine the number of atoms of each element. 2 calcium atoms4 nitrogen atoms12 oxygen atomsFor Oxygen:For Calcium:For Nitrogen:2Ca(NO3)222x___6distribute - just like math class!coefficientsubscript2 x 1 = 22 x 2 = 42 x 6 = 12
12 Balancing equations: Al + O2 Al2O3 Step 1: Determine the formulas for reactants and productsStep 2: Write reactants on the left and products on the rightExample:Aluminum + oxygen aluminum oxideAl + O2 Al2O3
13 Step 3: Count the number of each element in the reactants and products. Al + O2 Al2O31 Al, 2 O 2 Al, 3 OStep 4: Balance the elements one at a time by using coefficients (you should not write 1s). Do not change the formulas as you balance!4Al + 3O2 2Al2O34 Al, 6 O Al, 6 O
14 Finally,Step 5: Check to make sure each atom is balanced, and make sure all the balanced coefficients are in the lowest possible ratio.
15 CH4 + 2O2 → CO2 + 2H2O Reactants 1 carbon atom 4 hydrogen atoms 2 oxygen atomsProducts1 carbon atom2 hydrogen atoms3 oxygen atoms4 hydrogen atoms4 oxygen atoms4 oxygen atomsWhat went in came out…the reaction is balanced!
16 CH4 + 2O2 → CO2 + 2H2O What went in came out… the reaction is balanced!
18 Practice 1. The reaction below shows the process of oxidizing iron Practice 1. The reaction below shows the process of oxidizing iron. Balance the equation by calculating the coefficients.2, 3, 11, 1, 14, 3, 24, 2, 2432
19 Practice 2. Which chemical equation Practice 2. Which chemical equation supports the law of conservation of mass?2H2O → H2 + O2Zn + HCl → ZnCl2 + H2Al4C3 + H2O → CH4 + Al(OH)3CH4 + 2O2 → CO2 + 2H2O
20 22Practice 3. What are the coefficients that will balance the chemical reaction above?2, 1, 13, 4, 22, 2, 14, 3, 2
21 2K + 2H2O → 2KOH + H2Practice 4. What is the coefficient for H2O when the equation above is balanced?1234
22 Ways to Classify Reactions There are 5 general types of chemical reactions:CombinationDecompositionSingle-replacementDouble replacementCombustion
23 Types of ReactionsCombination or synthesis reactions- occur when two elements combine to form a single compound as a product.X + Y XYA synthesis reaction may also involve the combination of an element plus a compound or the combination of two compounds, always forming a single compound as a product.
24 Examples:Ca + Cl2 CaCl2PCl3 + Cl2 PCl5Na2O + H2O 2NaOHRules to remember:Any metallic oxide plus water yields a metallic hydroxide, as inK2O + H2O 2KOHAny nonmetallic oxide plus water yields an acidN2O H2O 2HNO3
25 Decomposition reaction- occurs where one compound breaks down into two or more elements or compounds. Heat, electricity, or a catalyst is usually necessary.XY X + YExamples:2NaCl 2Na + Cl2H2SO3 H2O + SO2
26 Rules to remember:When heated, metal carbonates break down to yield metal oxides and carbon dioxideExample: MgCO3 MgO + CO2Hydrogen peroxide breaks down into water and oxygen gasH2O2 H2O + O2Carbonic acid decomposes into water and carbon dioxideH2CO3 H2O + CO2
27 Single replacement reaction (or single displacement)… occurs when one element displaces another element in a compound.A new element and a new compound are formed.A + BC B + AC
28 Details about single replacement reactions… Active metals displace less active metals or hydrogen from their compounds in aqueous solution. Consult an activity series of metals.A + BY AY + B
30 In general, Group I and Group II metals and aluminum are most active, transition metals are more active than hydrogen, and the jewelry metals (Cu, Ag, Au) and Hg are the least active. You do not need to memorize the activity series.Examples:Mg + NiCl2 Zn + CuSO4 2HNO Pb
31 More single replacement… Some nonmetals can also displace other nonmetals: active halogens replace less active halogens from their compounds in aqueous solution.Fluorine at the top of group 7A is the most active, with activity decreasing as you move down the group.MX + Y MY + X
32 b) Some nonmetals can also react in single replacement reactions: active halogens replace less active halogens from their compounds in aqueous solutions. Fluorine at the top of the group is the most active, with the activity decreasing as you move down the group.Examples:2NaCl + F2 NaF + Cl2Cl KI 2KCl + I2
33 Double replacement reactions Two compounds (in aqueous solution) react to form two new compounds. These are also called exchange reactions.AB + CD AD + CB
34 Double replacement reactions require one of three kinds of chemical change: Formation of a precipitate (solid)Formation of a gasFormation of water
35 Types of double replacement… Formation of a precipitate(a solid product)BaNO3(aq) + K2CrO4(aq) 2KNO3(aq) + BaCrO4(s)
36 Types of double replacement… Formation of a gasSince H2CO3 and H2SO3 are unstable, if produced in a reaction, they will decompose.H2CO3 decomposes into H2O and CO2.H2SO3 decomposes into H2O and SO2.
37 Types of double replacement… Formation of waterIncludes acid-base reactions…acid + base water and saltHCl + NaOH NaCl + H2O
38 Combustion Reactions Involve combining with oxygen These reactions produce energy so rapidly that a flame resultsCH4(g) + 2O2(g) CO2(g) + 2H2O(g)