Chemical Reactions Ch. 11 Chemical Reactions when a substance changes identity Reactants - original Products - resulting law of conservation of mass total mass of reactants = total mass of products In other words, the number and type of atoms in a reaction don t t change, just how they are bonded. Chemical Reactions Chemical Reactions chemical equation - represents identities and relative amounts of reactants and products in the chemical reaction CH 4 + 2 O 2 CO 2 + 2 H 2 O That equation means 1 methane (CH 4 ) molecule reacts with 2 oxygen molecules and produces 1 carbon dioxide molecule and 2 water molecules. The + sign just divides each reactant and products. The separates the before (reactants) from the after (products) Notice the 2 (its called a coefficient) in front of O 2 and H 2 O this is needed to maintain the Law of Conservation of Mass. Its called Balancing the Equation
Writing Chemical Equations most pure elements are written as their elemental symbol (C, Zn, Mg, Cu, etc.) diatomic molecules H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2 When written as a pure substance these 7 elements are always written this way. C + O 2 CO 2 Word Equations A description just describes what is physically happening A word equation simplifies the description, but uses names instead of chemical formulas (helps you to write formula equation) Example Symbols Used in Equations Description: Solid sodium oxide is added to water at room temperature and forms sodium hydroxide. Word Equation: sodium oxide + water sodium hydroxide Formula Equation: Na 2 O + H 2 O NaOH Before its balanced its called the skeleton equation above arrow: or heat MnO 2 or Pt 25 C requirement yields reversible heated catalyst 25 C specific Temperature 2 atm specific Pressure requirement after a formula: Phase/state of the chemical (s) (l) (aq) (g) solid liquid aqueous: dissolved in water gas
Equations cannot tell us: if the reaction will actually occur depends on many factors affecting energy the speed of the reaction depends on chemical kinetics can be very slow, almost unnoticeably how the bonding actually changes formula may not clearly show bonding Types of Chemical Reactions Hints of Chemical Rxn heat or light can also happen with physical changes gas bubbles means a gas is being created as product precipitate solid is being created color change Types of Chemical Reactions 5 basic types discussed here not all reactions fall in these categories you should be able to: categorize a reaction by its reactant(s) predict the product(s)
1. Synthesis / Combination also called composition reaction reactants: more than one can be elements or compounds products: only one compound A + X AX 1. Synthesis / Combination Rubidium and sulfur Rb(s) + S 8 (s) Rb 2 S(s) Magnesium and oxygen Mg(s) + O 2 (g) MgO(s) Sodium and chlorine Na(s) + Cl 2 (g) NaCl(s) Magnesium and fluorine Mg(s) + F 2 (g) MgF 2 (s) 1. Synthesis / Combination calcium oxide and water CaO(s) + H 2 O(l) Ca(OH) 2 (aq) sulfur dioxide and water SO 2 (g) + H 2 O(l) H 2 SO 3 (aq) calcium oxide and sulfur dioxide CaO(s) + SO 2 (g) CaSO 3 (s) 2. Decomposition opposite of synthesis usually require energy reactants: only one compound products: two or more Can either be elements or compounds AX A + X
2. Decomposition water H 2 O(l) H 2 (g) + O 2 (g) calcium carbonate CaCO 3 (s) CaO(s) + CO 2 (g) calcium hydroxide Ca(OH) 2 (s) CaO(s) + H 2 O(l) carbonic acid H 2 CO 3 (aq) CO 2 (g) + H 2 O(l) 3. Single Replacement an element replaces a similar element in a compound reactants: 1 element & 1 compound products: 1 element & 1 compound A + BX B + AX Y + AX X + AY 3. Single Replacement zinc and hydrochloric acid Zn(s) + HCl(aq) ZnCl 2 (aq) + H 2 (g) iron and water Fe(s) + H 2 O(l) FeO(aq) + H 2 (g) magnesium and lead (II) nitrate Mg(s) + Pb(NO 3 ) 2 (aq) Mg(NO 3 ) 2 (aq) + Pb(s) chlorine and potassium bromide Cl 2 (g) + KBr(s) KCl(s) + Br 2 (g) 4. Double Replacement two similar elements switch places reactants: 2 compounds products: 2 compounds AX + BY BX + AY
4. Double Replacement barium chloride and sodium sulfate BaCl 2 (aq) + Na 2 SO 4 (aq) NaCl(aq) + BaSO 4 (s) iron sulfide and hydrochloric acid FeS(aq) + HCl(aq) FeCl 2 (aq) + H 2 S(g) hydrochloric acid and sodium hydroxide HCl(aq) + NaOH NaCl(aq) + H 2 O(l) potassium iodide and lead (II) nitrate KI(aq) + Pb(NO 3 ) 2 KNO 3 (aq) + PbI 2 (s) 5. Combustion A hydrocarbon combines with oxygen A hydrocarbon is a compound made of C and H (and possibly O) Heat and light are released in the reaction Products are CO 2 and H 2 O Ex: CH 4 + O 2 CO 2 + H 2 O Combustion Octane and oxygen C 8 H 18 (g) + O 2 (g) CO 2 (g) + H 2 O(g) propane and oxygen C 3 H 8 (g) + O 2 (g) CO 2 (g) + H 2 O(g) Practice Classify each of the following reactions one of the five basic types: Na 2 O + H 2 O NaOH synthesis Zn (s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) Ca(s) + 2H 2 O(l) Ca(OH) 2 (aq) + H 2 (g)
Practice 2H 2 O 2 (aq) O 2 (g) + 2H 2 O(l) decomposition Cu(s) + 2AgNO 3 (aq) 2Ag(s) +Cu(NO 3 ) 2 (aq) C 2 H 4 (g) + O 2 (g) CO 2 (g) + H 2 O(g) combustion ZnO(s) + C(s) 2Zn(s) + CO 2 (g) Practice Na 2 O(s) + 2CO 2 (g) + H 2 O(l) NaHCO 3 (s) synthesis Ca(s) + H 2 O(l) Ca(OH) 2 (aq) + H 2 (g) KClO 3 (s) KCl(s) + O 2 (g) decomposition H 2 SO 4 (aq) + BaCl 2 (aq) HCl(aq) + BaSO 4 (s) double replacement Activity Series Ch. 11 Chemical Equations and Reactions Activity Series Activity ability of an element to react easier it reacts, higher the activity activity series list of elements organized according to activities from highest to lowest
Activity Series metals greater activity, easier to lose electrons easier to become a cation nonmetals greater activity, easier to gain electrons easier to become an anion Activity Series used to predict whether single replacement reactions will occur most active is on top an element can replace anything below it but not any above it Activity Series Practice calcium and lead (II) nitrate Ca + Pb(NO 3 ) 2 Ca + Pb(NO 3 ) 2 Ca(NO 3 ) 2 + Pb copper and lithium sulfate Cu + Li 2 SO 4 no reaction bromine and iron (II) chloride Br 2 + FeCl 2 no reaction zinc and hydrochloric acid Zn + HCl ZnCl 2 + H 2