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Chemical Equations Chemistry. Evidence of a chemical reaction: A reaction has occurred if the chemical and physical properties of the reactants and products.

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Presentation on theme: "Chemical Equations Chemistry. Evidence of a chemical reaction: A reaction has occurred if the chemical and physical properties of the reactants and products."— Presentation transcript:

1 Chemical Equations Chemistry

2 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

3 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.

4 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

5 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” also indicate that a substance is dissolved in water (usually) -- acids are aqueous solutions

6 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)

7 precipitate: a solid product that forms in an aqueous solution reaction Na 2 CO 3 + Ca(NO 3 ) 2 CaCO 3 + (aq) (aq) Na 1+ Ca 2+ CO 3 2– NO 3 1– 2 (aq) (s) Na 1+ NaNO 3 NO 3 1– 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”

8 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

9 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

10 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) ___Fe 2 (s) + ___O 3 (g)___Fe 2 O 3 (s)

11 Changing a ___________ changes the substance. To balance, modify only _____________. Right now, _______________ don’t 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

12 2 solid sodium reacts w/oxygen to form solid sodium oxide ___O 2 (g) ___Na(s) ___Na 2 O(s) + Na 1+ 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 1– _ Al 2 (SO 4 ) 3 (s) + _ CaCl 2 _ CaSO 4 _ AlCl 3 (aq)

13 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) _ 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 Furnaces burn primarily methane.

14 2 _ 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 ** _ C 5 H 12 + _ O 2 _ CO 2 + _ H 2 O ** 856 ** = complete combustion of a hydrocarbon yields CO 2 and H 2 O Write equations for the combustion of C 7 H 16 and C 8 H _ C 7 H 16 + _ O 2 _ CO 2 + _ H 2 O _ C 8 H 18 + _ O 2 _ CO 2 + _ H 2 O

15 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

16 decomposition: complex substances are broken down into simpler ones lithium chlorate lithium chloride + oxygen water hydrogen gas + oxygen gas Li 1+ ClO 3 1– Li 1+ Cl 1– _ LiClO 3 1 _ LiCl + _ O _ H 2 O 2 _ H 2 + _ O 2 21 AB A + B ABC AB + C ABC A + B + C

17 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 1+ Br 1– _ NaBr 1 _ Br 2 + Na 1+ Cl 1– _ NaCl Cu 2+ SO 4 2– _ CuSO 4 _ Al + Al 3+ SO 4 2– _ Al 2 (SO 4 ) 3 1 _ Cu copper aluminum sulfate +

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

19 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

20 (?) 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 1+ OH 1– Fe 3+ Cl 1– NO 3 1– Pb 2+ NO 3 1– K 1+ I 1– Pb 2+ NO 3 1– K 1+ I 1– Check new combinations to decide. (?) K 1+ SO 4 2– Cu 2+ H 1+ OH 1– K 1+ SO 4 2– (?) Cl 1– Cu 2+ (?) Fe 3+ NO 3 1– (?) (ppt)(aq) (water) (aq) NR _ K 2 SO 4 (aq) + _ H 2 O (l) _ PbI 2 (s) + _ KNO 3 (aq)

21 Ions in Aqueous Solution Pb(NO 3 ) 2 (s) Pb(NO 3 ) 2 (aq) Pb 2+ (aq) + 2 NO 3 1– (aq) add water dissociation: Pb 2+ NO 3 1– Pb 2+ NO 3 1– “splitting into ions” NaI(s) NaI(aq) Na 1+ (aq) + I 1– (aq) Na 1+ I 1– Na 1+ I 1– add water

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

23 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 1– (aq)Ba 2+ (aq) + 2 OH 1– (aq) Ba 2+ OH 1– Zn 2+ NO 3 1– clear Zn(NO 3 ) 2 solutionclear Ba(OH) 2 solution

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

25 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.

26 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

27 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.

28 When going from moles of one substance to moles of another, use coefficients from balanced equation. part. vol. mass MOL mass vol. part. MOL SUBSTANCE “A” SUBSTANCE “B” (known) (unknown) Use coeff. from balanced equation in crossing this bridge 4 Na(s) + 1 O 2 (g) 2 Na 2 O(s)

29 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 = 4.2 mol O mol Na = 43.6 mol Na 2 O () 2 mol Na 2 O 4 mol Na mol Na 2 O = mol Na () 2 mol Na 2 O 4 mol Na O2O2 NaNa 2 O Na

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