Unit 7: Chemical Equations Chemistry. In a reaction: atoms are rearranged AND mass energy charge are conserved Balancing Chemical Equations = law of conservation

Unit 7: Chemical Equations Chemistry

In a reaction: atoms are rearranged AND mass energy charge are conserved Balancing Chemical Equations = law of conservation of mass same # of atoms of each type on each side of equation

CH 4 + 2 O 2 CO 2 + 2 H 2 O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

EX. solid iron reacts with oxygen gas to yield solid iron (III) oxide If all coefficients are 1 If we change subscripts Fe 3+ O 2 ___Fe(s) + ___O 2 (g) ___Fe 2 O 3 (s) + ___Fe(s) + ___O 2 (g)___Fe 2 O 3 (s) 1 1 1 ___Fe 2 (s) + ___O 3 (g)___Fe 2 O 3 (s) 1 1 1 + But we cant!!!

Changing a ___________ changes the substance. To balance, modify only _____________. Right now, _______________ dont enter into our balancing picture. subscript coefficients superscripts ___Fe(s) + ___O 2 (g)___Fe 2 O 3 (s) + 23 Hint: Start with most complicated substances first and leave simplest substances for last. 4

2 solid sodium reacts w/oxygen to form solid sodium oxide ___O 2 (g) ___Na(s) ___Na 2 O(s) + Na + O 2 + 14 Aqueous aluminum sulfate reacts w/aqueous calcium chloride to form a white precipitate of calcium sulfate. The other compound remains in solution. Al 3+ SO 4 2 Ca 2+ Cl _ Al 2 (SO 4 ) 3 (s) + _ CaCl 2 _ CaSO 4 _ AlCl 3 (aq) + 1332

1 1 Methane gas (CH 4 ) reacts with oxygen to form carbon dioxide gas and water vapor. _ CH 4 (g) + _ O 2 (g) _ CO 2 (g) _ H 2 O(g) + 212 _ CaC 2 (s) + _ H 2 O(l) _ C 2 H 2 (g) + _ CaO(s) _ CaSi 2 + _ SbI 3 _ Si + _ Sb + _ CaI 2 _ Al + _ CH 3 OH _ Al(CH 3 O) 3 + _ H 2 111 32263 3 26 2 13 Furnaces burn primarily methane.

2 _ C 2 H 2 (g) + _ O 2 (g) _ CO 2 (g) + _ H 2 O(l) ** 5 42 121 1 _ C 3 H 8 + _ O 2 _ CO 2 + _ H 2 O ** 534 1 _ C 5 H 12 + _ O 2 _ CO 2 + _ H 2 O ** 856 ** = complete combustion (+ O 2 ) of a hydrocarbon (C x H y ) yields CO 2 and H 2 O Write equations for the combustion of C 7 H 16 and C 8 H 18 1 _ C 7 H 16 + _ O 2 _ CO 2 + _ H 2 O 1178 1 _ C 8 H 18 + _ O 2 _ CO 2 + _ H 2 O 2589 21618 Odd # Oxy

Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: change in colorchange in odorproduction of new gases or vapor input or release of energy difficult to reverse release input

Evidence of a chemical reaction: A reaction has occurred if the chemical and physical properties of the reactants and products differ. heat light sound gas emitted color change odor For a reaction to occur, particles of reactants must collide, and with sufficient energy collision theory

activation energy: Chemical reactions release or absorb energy. energy needed to start a reaction exothermic reactions endothermic reactions The reaction in an oxy- acetylene torch is exothermic. Photosynthesis is an endothermic reaction.

Endothermic Reaction Energy + Reactants Products Reaction progress Energy Reactants Products Activation Energy

Exothermic Reaction Reactants Products + Energy 10 energy = 8 energy + 2 energy Reactants Products Energy Energy of reactants Energy of products Reaction Progress

Decomposition of Nitrogen Triiodide 2 NI 3 (s) N 2 (g) + 3 I 2 (g) NI 3 I2I2 N2N2

catalyst: speeds up reaction w/o being consumed it lowers the activation energy (E a ) AE timetime without catalystwith catalyst Examples: enzymes catalyze biochemical reactions catalytic converters convert CO into CO 2 Energy

Reaction Conditions and Terminology Certain symbols give more info about a reaction (s) = solid (l) = liquid (g) = gas (aq) = aqueous (dissolved in H 2 O) NaCl(s) NaCl(aq) More on aqueous soluble or in solution indicates that a substance is dissolved in water (usually) all acids are aqueous solutions

Other symbols means... Temp. at which we perform rxn. might be given. The catalyst used might be given. means ______ is added to the reaction MgCO 3 (s) MgO(s) + CO 2 (g) C 2 H 4 (g) + H 2 (g)C 2 H 6 (g) Pt C 6 H 5 Cl + NaOHC 6 H 5 OH + NaCl 400 o C yields or produces heat (i.e., clues about the reaction)

Factors that influence the rate of a reaction To make reaction rate increase concentration of reactants particle size temperature mechanical mixing pressure catalystuse one nature of reactantsN/A

Types of Chemical Reactions Synthesis (combination) reaction Decomposition reaction A Single-replacement reaction B Double-replacement reaction Combustion reaction (of a hydrocarbon) A + B AB AB A + B A + BC AC + B AB + CD AD + CB C x H y + O 2 CO 2 + H 2 O A use activity series to predict products/reactivity B use solubility chart to predict products/reactivity elementcompoundelementcompound All compounds

Classifying Reactions four types synthesis: simpler substances combine to form more complex substances oxygen + rhombic sulfur sulfur dioxide sodium + chlorine gas sodium chloride A + B AB AB + C ABC A + B + C ABC __ O 2 __ S 8 + __ SO 2 __ Na __ Cl 2 + __ NaCl 818 212

decomposition: complex substances are broken down into simpler ones lithium chlorate lithium chloride + oxygen water hydrogen gas + oxygen gas Li + ClO 3 Li + Cl _ LiClO 3 _ LiCl + _ O 2 2 2 3 _ H 2 O 2 _ H 2 + _ O 2 21 AB A + B ABC AB + C ABC A + B + C

single-replacement: one element replaces another AB + C A + CBAB + C B + AC chlorine sodium bromide sodium chloride bromine ++ ? aluminum copper (II) sulfate + _ Cl 2 Na + Br _ NaBr 1 _ Br 2 + Na + Cl _ NaCl + 221 Cu 2+ SO 4 2 _ CuSO 4 _ Al + Al 3+ SO 4 2 _ Al 2 (SO 4 ) 3 1 _ Cu + 323 copper aluminum sulfate +

double-replacement: AD + CB AB + CD iron (III) chloride + potassium hydroxide ? Fe 3+ Cl _ FeCl 3 + 1 K+K+ OH _ KOH Fe 3+ OH K + Cl _ KCl_ Fe(OH) 3 + 313 iron (III) hydroxide + potassium chloride lead (IV) nitrate + calcium oxide ? Pb 4+ O 2 _ Pb(NO 3 ) 4 + 1 Ca 2+ NO 3 _ CaO_ Ca(NO 3 ) 2 _ PbO 2 + 212 Pb 4+ O 2 Ca 2+ NO 3 lead (IV) oxide + calcium nitrate

Balance and classify the following reactions: _ F 2 _ MgI 2 1 _ I 2 + _ MgF 2 + 111 Single replacement _ C 3 H 5 N 3 O 9 4 _ N 2 + _ CO 2 6 12 + _ H 2 O 10 + _ O 2 1 Decomposition 1 _ C 5 H 12 + _ O 2 _ CO 2 + _ H 2 O 856 Double Replacement? Combustion

Word Equations Solid iron reacts with oxygen gas to yield solid iron(III) oxide. word equation: balanced equation: iron Fe +oxygen iron(III) oxide O 2 + Fe 3+ O 2 Fe 2 O 3 243

2 Solid sodium reacts w /oxygen to form solid sodium oxide. O 2 (g) Na(s) Na 2 O(s) + Na + O 2 + 4 Aqueous aluminum sulfate reacts w /aqueous calcium chloride to form a white precipitate of calcium sulfate. The other compound remains in solution. Al 3+ SO 4 2 Ca 2+ Cl Al 2 (SO 4 ) 3 (s) + CaCl 2 CaSO 4 AlCl 3 (aq) + 332 Write a balanced equation ( w /rxn conditions) from the following word equations.

Single and Double Replacement Reactions Double-replacement reaction CaCO 3 + 2 HCl CaCl 2 + H 2 CO 3 General form: AB + CD AD + CB Single-replacement reaction Mg + CuSO 4 MgSO 4 + Cu General form: A + BC AC + B

single-replacement: one element replaces another AB + C A + CBAB + C B + AC chlorine sodium bromide sodium chloride bromine ++ ? aluminum copper (II) sulfate + _ Cl 2 Na + Br _ NaBr 1 _ Br 2 + Na + Cl _ NaCl + 221 Cu 2+ SO 4 2 _ CuSO 4 _ Al + Al 3+ SO 4 2 _ Al 2 (SO 4 ) 3 1 _ Cu + 323 copper aluminum sulfate +

Ca Activity Series Foiled again: Aluminum is knocked out by Calcium Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H 2 Cu Hg Ag Pt Au Halogen Reactivity F 2 Cl 2 Br 2 I 2 Printable Version of Activity Series Printable Version of Activity Series

Mg + AlCl 3 Al + MgCl 2 Predict if these reactions will occur Al + MgCl 2 Can magnesium replace aluminum? Activity Series YES, magnesium is more reactive than aluminum. 2233 Can aluminum replace magnesium? NO, magnesium is less reactive than aluminum. Therefore, no reaction will occur. NR (No Reaction) MgCl 2 + Al No reaction We must determine if the lone element is more reactive than the bonded one metals replace metals or non-metals replace nonmetals Order of reactants DOES NOT determine how they react.

1 How do we know if a reaction will occur? For single-replacement reactions, use Activity Series. In general, elements above replace elements below. _ Ba + _ FeSO 4 _ Mg + _ Cr(ClO 3 ) 3 _ Pb + _ Al 2 O 3 _ NaBr + _ Cl 2 _ FeCl 3 + _ I 2 _ CoBr 2 + _ F 2 _ Fe + _ BaSO 4 _ Cr + _ Mg(ClO 3 ) 2 NR _ NaCl + _ Br 2 NR _ CoF 2 + _ Br 2 111 3223 21 11 21 11

double-replacement: AD + CB AB + CD iron (III) chloride + potassium hydroxide ? Fe 3+ Cl _ FeCl 3 + 1 K+K+ OH _ KOH Fe 3+ OH K + Cl _ KCl_ Fe(OH) 3 + 313 iron (III) hydroxide + potassium chloride lead (IV) nitrate + calcium oxide ? Pb 4+ O 2 _ Pb(NO 3 ) 4 + 1 Ca 2+ NO 3 _ CaO_ Ca(NO 3 ) 2 _ PbO 2 + 212 Pb 4+ O 2 Ca 2+ NO 3 lead (IV) oxide + calcium nitrate

Formation of a solid: AgCl AgNO 3 (aq) + KCl(aq) KNO 3 (aq) + AgCl(s) Double Replacement Reactions

precipitate: a solid product that forms in an aqueous solution reaction When ionic substances have (aq) written after them, the individual ions have dissociated from the ionic crystal and are floating around separately. Na 3 PO 4 (aq) means3 Na + (aq) + PO 4 3 (aq) Sodium phosphate, Na 3 PO 4, (sometimes called sodium phosphate, tribasic) is a cleaning agent and food preservative.

precipitate: a solid product that forms in an aqueous solution reaction Na 2 CO 3 + Ca(NO 3 ) 2 CaCO 3 + (aq) (aq) Na + Ca 2+ CO 3 2 NO 3 2 (aq) (s) Na + NaNO 3 NO 3 ppt clear Na 2 CO 3 solution clear Ca(NO 3 ) 2 solution cloudy solution containing CaCO 3 (s) and NaNO 3 (aq) chunks sinkies floaties

FeCO 3 Na + Fe 2+ iron (II) chloride + sodium carbonate Cl 2 Using the SOLUBILITY TABLE: sodium chloride is soluble iron (II) carbonate is insoluble CO 3 Fe 2+ Fe Na + Na 2 Cl - CO 3 2- Cl- CO 3 2- NaCl sodium chloride iron (II) carbonate + (aq) (s) 2 FeCl 2 Na 2 CO 3 NaCl FeCO 3 (aq) (s) ++ Predict if a reaction will occur when you combine aqueous solutions of iron (II) chloride and sodium carbonate If the reaction does occur, write a balanced chemical equation showing it (be sure to include phase notation). (aq) Balanced chemical equation

(?) For double-replacement reactions, reaction will occur if any product is: water a gas a precipitate driving forces _ Pb(NO 3 ) 2 (aq) + _ KI (aq) _ KOH (aq) + _ H 2 SO 4 (aq) _ FeCl 3 (aq) + _ Cu(NO 3 ) 2 (aq) H+H+ OH Fe 3+ Cl NO 3 Pb 2+ NO 3 K+K+ II Pb 2+ NO 3 K+K+ II Check new combinations to decide. (?) K+K+ SO 4 2 Cu 2+ H+H+ OH K+K+ SO 4 2 (?) Cl Cu 2+ (?) Fe 3+ NO 3 (?) (ppt)(aq) (water) (aq) NR _ K 2 SO 4 (aq) + _ H 2 O (l) _ PbI 2 (s) + _ KNO 3 (aq) 1212 2112

Ions in Aqueous Solution Pb(NO 3 ) 2 (s) Pb(NO 3 ) 2 (aq) Pb 2+ (aq) + 2 NO 3 (aq) add water dissociation: Pb 2+ NO 3 Pb 2+ NO 3 splitting into ions NaI(s) NaI(aq) Na + (aq) + I (aq) Na + II II add water ChemThink

Mix them and get the overall ionic equation __Pb 2+ (aq) + __NO 3 (aq) + __Na + (aq) + __I (aq) __PbI 2 (s) + __NO 3 (aq) + __Na + (aq) yields reactants products Cancel spectator ions to get net ionic equation __PbI 2 (s) 1 1222 221 Pb 2+ NO 3 Na + II NO 3 Na + II __Pb 2+ (aq) + __I (aq) 12 Pb 2+ II II II II II II

Mix together Zn(NO 3 ) 2 (aq) and Ba(OH) 2 (aq): Zn(NO 3 ) 2 (aq) Ba(OH) 2 (aq) Zn 2+ (aq) + 2 NO 3 (aq)Ba 2+ (aq) + 2 OH (aq) Ba 2+ OH Zn 2+ NO 3 clear Zn(NO 3 ) 2 solutionclear Ba(OH) 2 solution

Mix them and get the overall ionic equation __Zn 2+ (aq) + __NO 3 (aq) + __Ba 2+ (aq) + __OH (aq) __Zn(OH) 2 (s) + __NO 3 (aq) + __Ba 2+ (aq) yields reactants products Cancel spectator ions to get net ionic equation __Zn(OH) 2 (s) 1 1212 121 Zn 2+ NO 3 OH NO 3 __Zn 2+ (aq) + __OH (aq) 12 Zn 2+ OH Ba 2+ Zn 2+ OH Zn 2+ OH

Polymers and Monomers polymer: a large molecule (often a chain) made of many smaller molecules called monomers Polymers can be made more rigid if the chains are linked together by way of a cross-linking agent.

MonomerPolymer amino acids nucleotides ( w /N- bases A,G,C,T/U).. styrene PVA. proteins nucleic acids polystyrene slime polyvinyl alcohol HNCCOH H H O R

Quantitative Relationships in Chemical Equations 4 Na(s) + O 2 (g) 2 Na 2 O(s) Particles4 atoms1 mcule2 mcules Moles4 mol1 mol2 mol Grams4 g1 g2 g ** Coefficients of a balanced equation represent # of particles OR # of moles, but NOT # of grams.

Part. Vol. Mass MOL Mass Vol. Part. MOL SUBSTANCE A SUBSTANCE B (known) (unknown) Use coeff. from bal. eq. to go from moles of A to moles of B

Na 2 O 4 Na(s) + O 2 (g) 2 Na 2 O(s) How many moles oxygen will react with 16.8 moles sodium? How many moles sodium oxide are produced from 87.2 moles sodium? How many moles sodium are required to produce 0.736 moles sodium oxide? () 4 mol Na 1 mol O 2 16.8 mol Na = 4.20 mol O 2 87.2 mol Na = 43.6 mol Na 2 O () 2 mol Na 2 O 4 mol Na 0.736 mol Na 2 O = 1.47 mol Na () 2 mol Na 2 O 4 mol Na O2O2 NaNa 2 ONa

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Unit 7: Chemical Equations Chemistry. In a reaction: atoms are rearranged AND mass energy charge are conserved Balancing Chemical Equations = law of conservation