Presentation on theme: "IIIIIIIVV Unit 5 – Chemical Reactions Chapter 9. A.Signs of a Chemical Reaction Evolution of heat and light Formation of a gas Formation of a precipitate."— Presentation transcript:
IIIIIIIVV Unit 5 – Chemical Reactions Chapter 9
A.Signs of a Chemical Reaction Evolution of heat and light Formation of a gas Formation of a precipitate Color change
B.Law of Conservation of Mass mass is neither created nor destroyed in a chemical reaction 4 H 2 O 4 H 2 O 4 g32 g 36 g n total mass stays the same n atoms can only rearrange
C. Chemical Equations A+B C+D REACTANTSPRODUCTS
p. 283 C. Chemical Equations
D. Writing Equations Identify the substances involved. Use symbols to show: 2H 2 (g) + O 2 (g) 2H 2 O(g) How many? - coefficient Of what? - chemical formula In what state? - physical state n Remember the diatomic elements.
D. Writing Equations Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two units of aqueous aluminum chloride. How many? Of what? In what state? Al 2(s)(s)+ 3CuCl 2 (aq) 3 Cu(s)(s)+ 2AlCl 3 (aq)
E. Describing Equations Describing Coefficients: individual atom = “atom” covalent substance = “molecule” ionic substance = “unit” 3 molecules of carbon dioxide 2 atoms of magnesium 4 units of magnesium oxide 3CO 2 2Mg 4MgO
E. Describing Equations to produce How many? Of what? In what state? Zn(s) + 2HCl(aq) ZnCl 2 (aq) + H 2 (g) One atom of solid zinc reacts with two molecules of aqueous hydrochloric acid one unit of aqueous zinc chlorideand one molecule of hydrogen gas.
F. Chemical vs. Physical (revisited) Chemical changes – make something new Ex: sodium and chlorine react to make table salt Physical changes – just change the physical nature of the substance (the chemical formula remains the same) Ex: Ice melts into liquid water (formula remains H 2 O)
A. Balancing Steps 1.Write the unbalanced equation. 2.Count atoms on each side. 3.Add coefficients to make #s equal. Coefficient subscript = # of atoms 4.Reduce coefficients to lowest possible ratio, if necessary. 5.Double check atom balance!!!
B. Helpful Tips Balance one element at a time. Update ALL atom counts after adding a coefficient. If an element appears more than once per side, balance it last. Balance polyatomic ions as single units. “1 SO 4 ” instead of “1 S” and “4 O”
Al + CuCl 2 Cu + AlCl 3 Al Cu Cl 3 6 C. Balancing Example Aluminum and copper(II) chloride react to form copper and aluminum chloride. 2 2 6
IIIIIIIVV 9.2 – Classifying Chemical Reactions
A. Combustion the burning of any substance in O 2 to produce heat CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(g) A + O 2 B
Na(s)+ O 2 (g) C 3 H 8 (g)+ O 2 (g) A. Combustion Products: contain oxygen hydrocarbons form CO 2 + H 2 O CO 2 (g)+ H 2 O(g) Na 2 O(s) 4 2
B. Synthesis the combination of 2 or more substances to form a compound only one product A + B AB
B. Synthesis H 2 (g) + Cl 2 (g) 2 HCl(g)
Al(s)+ Cl 2 (g) AlCl 3 (s) B. Synthesis Product: ionic – cross-over charges covalent - hard to tell
C. Decomposition a compound breaks down into 2 or more simpler substances only ONE REACTANT AB A + B
C. Decomposition 2 H 2 O(l) 2 H 2 (g) + O 2 (g)
KBr(l) K(s) + Br 2 (l) 2 2 C. Decomposition Products: binary - break into elements Diatomics – N 2, O 2, F 2, Cl 2, Br 2, I 2 others - hard to tell
D. Single Replacement one element replaces another in a compound metal replaces metal (+) nonmetal replaces nonmetal (-) A + BC B + AC
D. Single Replacement Cu(s) + 2AgNO 3 (aq) Cu(NO 3 ) 2 (aq) + 2Ag(s)
Fe(s)+ CuSO 4 (aq) Cu(s)+ FeSO 4 (aq) D. Single Replacement Products: Free element kicks out nonmetal nonmetal (-) free element on reactants side must be more active (check activity series) Br 2 (l)+ NaCl(aq) N.R.
AB + CD AD + CB E. Double Replacement ions in two compounds “change partners” cation of one compound combines with anion of the other
E. Double Replacement Pb(NO 3 ) 2 (aq) + K 2 CrO 4 (aq) PbCrO 4 (s) + 2KNO 3 (aq)
Pb(NO 3 ) 2 (aq)+ KI(aq) PbI 2 (s)+ KNO 3 (aq) E. Double Replacement Products: switch negative ions one product must be insoluble (check solubility table) NaNO 3 (aq)+ KI(aq) N.R. 2 2