Balancing Chemical Equations Chapter 8 Balancing Chemical Equations

8.1 Chemical Equations Chemical equations represent, with symbols and formulas, the reactants and products in a chemical reaction. reactants  products Requirements for all chemical equations: must show all reactants and products formulas must be correct Law of Conservation of Mass must be satisfied (equation must be balanced)

Chemical Equations Balanced Equations – use coefficients H2 + Cl2  2 HCl Hydrogen reacts with chlorine to yield hydrochloric acid Symbols used in equations 2NaCl(s)  2Na(s) + Cl2(g) NaCl(aq) - solution of sodium chloride in water H2O(l) – liquid water g or ↑ = gas

Chemical Equations More symbols  = one way reactions ↔ = reversible reaction ΔH = heat cat = catalyst (a substance that speeds up a reaction without being used up in the reaction) S or ppt or ↓ = precipitate (solid - only found on products side)

Chemical Equations Significance of chemical equations H2(g) + Cl2(g)  2 HCl (g) means… Atoms: 2 atoms of hydrogen gas react with 2 atoms of chlorine gas and yields 2 atoms of hydrogen, 2 atoms of chlorine Molecules: 1 molecule of hydrogen gas reacts with 1 molecule of chlorine gas and yields 2 molecules of hydrochloric acid Molar mass: H = 2.0; Cl = 71.0; HCl = 73.0

Balancing Chemical Equations Helpful hints to balancing…. 1 atom at a time Balance atoms that appear only 1X per side first Balance polyatomic ions as whole units Balance diatomic elements last Save H + O for last

Balancing Chemical Equations Examples __H2O(l)  __ H2(g) +__O2(g) __(NH4)2CO3 (aq)+__CaCl2(s)  __CaCO3(s) +__NH4Cl(aq)

Balancing Chemical Reactions __Al(s) + __Br2(g)  __AlBr3(s) __C2H5OH(g) + __O2(g)  __CO2(g) +__H2O(l)

Balancing Chemical Reactions NOT IN PACKET!! _C3H6 + _ O2  _ CO2 + _H2O

Balancing Chemical Equations Tin (IV) oxide + Carbon  Tin + Carbon monoxide SnO2(aq) + C(s)  Sn(s) + CO(g) SnO2(aq) + 2C(s)  Sn(s) + 2CO(g)

Balancing Chemical Equations Aqueous Iron (III) Chlorate reacts with solid calcium to yield calcium chlorate and solid iron Fe(ClO3)3(aq) + Ca (s)  Ca(ClO3)2(aq) + Fe(s) 2Fe(ClO3)3(aq) + 3Ca (s)  3Ca(ClO3)2(aq) + 2Fe(s)

8.2 Types of Chemical Reactions synthesis decomposition combustion single replacement double replacement Remember: You must first find the correct products, then balance the equation!

Types of Chemical Reactions Synthesis (direct combination) - needs energy to happen (usually heat) General formula A + B ---> AB 2H2 + O2 → 2H2O

Types of Chemical Reactions Synthesis Examples Ba + S  Mg + Cl2  Al + Cl2  Na + O2  REMEMBER TO BALANCE!!!!!!!!!! BaS MgCl2 AlCl3 Na2O

Types of Chemical Reactions Decomposition (analysis) - needs energy to happen (usually heat or electricity) general formula AB ---> A + B 2H2O → 2H2 + O2

Types of Chemical Reactions Examples FeCl3  HgO  CuSO4 · 5 H2O  Fe + Cl2 Hg + O2 CuSO4(s) + H2O(g)

Types of Chemical Reactions Combustion - the reaction of hydrocarbons and oxygen General Formula CxH y + O2  CO2 + H2O

Types of Chemical Reactions CH4 + O2 → CO2 + H2O C3H8 + O2 → CO2 + H2O C4H10 + O2 → CO2 + H2O C2H5OH + O2 → CO2 + H2O

Types of Chemical Reactions Single replacement - take place in aqueous solutions - need very little energy to happen Two Types Positive Ions Switch AB + M  MB + A Negative Ions Switch MB + X  MX + B

Types of Chemical Reactions Positive Ions Switch HI(aq) + Mg(s)  AlCl3(aq) + Ca(s)  Ca(s) + HOH(l)  MgI2(aq) + I2(s) CaCl2(aq) + Al(s) Ca(OH)2(aq) + H2(g)

Types of Chemical Reactions Negative Ions Switch NaCl + F2  BaS + O2  NaF + Cl2 BaO + S

Types of Chemical Reactions Double Replacement - aqueous solution - little energy - usually forms one soluble ionic product (aka - aqueous) and either a ppt, water, or a gas that bubbles out of water General Formula (molecule + molecule) AB + CD  CB + AD AgNO3 + NaCl → AgCl + NaNO3

Types of Chemical Reactions FeCl3 + NaOH  H2SO4 + NaOH  NH4Cl + NaOH  Fe(OH)3 + NaCl HOH + Na2SO4 NH4OH + NaCl

8.3 Activity Series of the Elements Another Lie!! : ) Some reactions happen and some don’t! Assume all synthesis, decomposition, and combustions happen Not all single or double displacement occur Single Replacement Use activity series Double Replacement Use solubility table

Activity Series of the Elements Rules for the single replacement activity series: Any single element above an element in a compound will replace it. The top 5 elements react with water. Metals above H react with acids (molecules that start with H – not water). The nonmetal reactivity series is F> Cl > Br...

Activity Series of the Elements Ca + H2O → Al + H2O → Al + HI → Ca(OH)2 + H2 No Rxn AlI3 + H2

Activity Series of the Elements Cu + HI  NaCl + F2  NaF + Cl2 → No Rxn NaF + Cl2 No Rxn

Solubility Table of the Elements Rules for double replacement reactions using a solubility table: If one of the products formed is water, the reaction happens. If a gas is formed, the reaction happens. If an insoluble product forms (I or Ss), the reaction happens

Solubility Table of the Elements Na2CrO4 + KCl → FeCl3 + KOH → HCl + NaOH → No Rxn Fe(OH)3(ppt) + KCl(aq) H2O(l) + NaCl(s)

Solubility Trends Cations Anions - General trend - very soluble - Na, K, ammonium very insoluble- Ag, Pb, Hg, transitions Anions - very soluble – nitrate for monatomics- F>Cl>Br .... very insoluble - carbonate, hydroxide, phosphate, sulfate sulfides - decompose General trend - As size decreases, solubility increases OR Heavier stuff doesn’t dissolve well

Showing Energy Changes in Equations endothermic - A + B + heat  C ΔH is positive exothermic - A + B  C + heat ΔH is negative

Some helpful notes on writing phases in chemical reactions Metals are solids (except Hg, Br) SR and DR reactions, reactants that are compounds are always aqueous. SR and DR reactions, products that are compounds should have their phases identified using a solubility chart (aqueous vs. precipitate) S and D reactions, ionic compounds are solids. In C reactions, the water, CO2, and O2 are gases. The hydrocarbon is hard to tell, but is usually a liquid after C=6 or higher. Most other covalent compounds are gases. Acids (chemicals starting with hydrogen) are always aqueous