Unit 7: Chemical Equations Honors Chemistry

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.

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

Factors that influence the rate of a reaction To make reaction rate increase… concentration of reactants particle size temperature mechanical mixing catalyst nature of reactants use one N/A

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

Changing a ________ changes the substance. To balance, modify only __________. Right now, ___________ don’t enter into our “balancing” picture. subscript coefficients superscripts The thermite reaction (2 Al + Fe 2 O 3  2 Fe + Al 2 O 3 ) releases enough heat that it is used for underwater welding.

SiCl 4 + H 2 O  SiO 2 + HCl SiClClClClHHOSiOOHCl HHO HCl 2 4 Rule of Thumb A: Save the simplest substances for last (i.e., choose a complex substance on each side first). Au 2 S 3 + H 2  Au + H 2 S AuAuSSSHHAuHHS HH HHS HH Au 332

V 2 O 5 + HCl  VOCl 3 + H 2 O VVOOOOOHClVOClClClHHO HCl HHO HCl VOClClCl 36 HCl 2

Hg(OH) 2 + H 3 PO 4  Hg 3 (PO 4 ) 2 + H 2 O HgOHOHHHH#HgHgHg##HHO Rule of Thumb B: If polyatomic ions are the same on both sides of the equation, balance them first. 362 HHH# HgOHOH HHO

CaC 2 (s) + H 2 O(l) C 2 H 2 (g) + CaO(s) CaSi 2 + Sb I 3 Si + Sb + Ca I 2 Al + CH 3 OH Al(CH 3 O) 3 + H C 2 H 2 (g) + O 2 (g) CO 2 (g) + H 2 O(l) ** C 3 H 8 + O 2 CO 2 + H 2 O ** 534 C 5 H 12 + O 2 CO 2 + H 2 O ** 856 ** = complete combustion of a hydrocarbon yields CO 2 and H 2 O

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… -- synonyms: “soluble” or “in solution” -- acids and bases 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)

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) means…3 Na + (aq) + PO 4 3– (aq) Sodium phosphate, Na 3 PO 4, (sometimes called “sodium phosphate, tribasic”) is a cleaning agent and food preservative.

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”

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) Write a balanced equation ( w /rxn conditions) from the following word equations.

Methane gas (CH 4 ) burns in oxygen. CH 4 (g) + O 2 (g) CO 2 (g) H 2 O(g) + 22 Much of the methane that is liberated during the extraction of petroleum is simply burned because the cost of transporting it is too high. Write an equation for the combustion of C 8 H 18. C 8 H 18 + O 2 CO 2 + H 2 O

Classifying Reactions four types synthesis: simpler substances combine to form more complex substances sodium + chlorine gas sodium chloride A + B AB AB + C ABC A + B + C ABC Na Cl 2 + NaCl 22

22 decomposition: complex substances are broken down into simpler ones lithium chlorate lithium chloride + oxygen Li + ClO 3 – Li + Cl – LiClO 3 LiCl + O 2 3 AB A + B ABC AB + C ABC A + B + C

single-replacement: one element replaces another AB + C A + CBAB + C B + AC ? aluminum copper(II) sulfate + Cu 2+ SO 4 2– CuSO 4 Al + Al 3+ SO 4 2– Al 2 (SO 4 ) 3 Cu copper aluminum sulfate +

double-replacement: AD + CB AB + CD lead(IV) nitrate + calcium oxide ? Pb 4+ O 2– Pb(NO 3 ) 4 + Ca 2+ NO 3 – CaO Ca(NO 3 ) 2 PbO lead(IV) oxide + calcium nitrate

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

(?) For double-replacement reactions, reaction will occur if any product is: water a gas a precipitate driving forces Pb(NO 3 ) 2 (aq) + K I (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+ I–I– Pb 2+ NO 3 – K+K+ I–I– 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) Pb I 2 (s) + KNO 3 (aq) 22 22

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 H–N–C–C–O–H H H O R

Quantitative Relationships in Chemical Equations 4 Na(s) + O 2 (g) 2 Na 2 O(s) Particles4 atoms1 m’cule2 m’cules 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 moles sodium oxide? () 4 mol Na 1 mol O mol Na = 4.20 mol O mol Na = 43.6 mol Na 2 O () 2 mol Na 2 O 4 mol Na mol Na 2 O = 1.47 mol Na () 2 mol Na 2 O 4 mol Na O2O2 NaNa 2 ONa

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