Chapter 9 Chemical Reactins NOTES Chemical Reactins Chemical reactin: Chemical change 4 Indicatrs f Chemical Change: (1) (2) (3) (4) Cnsist f reactants (starting materials) and prducts (substances frmed) Represented by a chemical equatin Uses symbls and frmulas t shw the identities and relative amunts f the reactants and prducts Symbl Symbls: Purpse + Separates tw r mre reactants r prducts Separates reactants frm prducts (s) (l) (g) (aq) Separates reactants frm prducts and indicates a reversible reactin Identifies a slid state Identifies a liquid state Identifies a gaseus state Identifies a water (aqueus) slutin Shws heat added H2SO4 Shws a catalyst added (Catalyst - smething that speeds up a chemical reactin, but is nt used up in the reactin)
Example f a Chemical Equatin Cmbustin Reactin: CH 4(g) + 2O 2(g) CO 2(g) + 2H 2O(l) Needs t be balanced (balance using cefficients 1:2:1:2): Reactants: 1 C; 4 H; 4 O Prducts: 1 C; 4 H; 4 O Wrd equatin: methane(g) + xygen(g) carbn dixide(g) + water(l) Balancing Chemical Equatins IMPORTANT: When hydrgen, nitrgen, xygen, flurine, chlrine, brmine, and idine are nt bnded t anything else in a chemical reactin they need t be written as diatmics (tw atms)! Diatmics: H 2, N 2, O 2, F 2, Cl 2, Br 2, and I 2. Balancing chemical equatins shws that has been beyed (mass f reactants = mass f prducts) Steps t balance a chemical equatin: (1) Write the skeletn equatin fr the reactin Ex) H 2(g) + Cl 2(g) HCl(g) (2) Cunt the atms f the elements in the reactants Ex) H 2 +Cl 2 2 atms H, 2 atms Cl (3) Cunt the atms f the elements in the prducts Ex) HCl 1 atm H, 1 atm Cl (4) Change the cefficients t make the number f atms f each element equal n bth sides f the equatin (trial and errr) Ex) H 2 + Cl 2 2HCl 2 atms H + 2 atms Cl 2 atms H, 2 atms Cl (5) Write the cefficients in their lwest pssible rati (reduce cefficients t the smallest whle numbers pssible) Ex) H 2(g) + Cl 2(g) 2HCl(g) Rati: 1:1:2 (1 H 2 t 1 Cl 2 t 2 HCl) (6) Check yur wrk Ex) H 2(g) + Cl 2(g) 2HCl(g) 2 atms H + 2 atms Cl 2 atms H, 2 Cl atms Law f cnservatin f mass is beyed!
Balancing Chemical Equatins Practice Prblem #1 Write and balance the reactin between slid calcium and slid sulfur t prduce slid calcium sulfide. Balancing Chemical Equatins Practice Prblem #2 Write and balance the reactin between methane and xygen t yield carbn dixide and water. Balancing Chemical Equatins Practice Prblem #3 Types f Chemical Reactins 5 Types f Chemical Reactins (1) Synthesis (2) Cmbustin (3) Decmpsitin (4) Single Replacement/Displacement (SR) (5) Duble Replacement/Displacement (DR)
TYPES OF CHEMICAL REACTIONS INFORMATION SCAVENGER HUNT Walk arund the classrm and lab area t find the missing infrmatin needed t fill in the table belw. Type f Chemical Reactin Descriptin Generic Equatin Example #1 Example #2 SYNTHESIS COMBUSTION DECOMPOSITION SINGLE REPLACEMENT (SR) DOUBLE REPLACEMENT (DR)
Synthesis Synthesis Reactin Practice Cmbustin Cmbustin Reactin Practice Decmpsitin Decmpsitin Reactin Practice
Single-replacement (SR) Accrding t the activity series, which helps t determine whether r nt a reactin will ccur, sme reactins might nt happen Ex) Ag(s) + Cu(NO 3) 2(aq) NR (NR = n reactin) Since Cpper (Cu) is mre reactive than Silver (Ag) the Cpper will stay reacted with nitrate (NO 3- ) the mre reactive element will end as a cmpund Single-replacement (SR) Reactin Practice
Duble-replacement (DR) All duble-replacement reactins will prduce either water, a precipitate (a slid), r a gas YOU MUST KNOW YOUR POLYATOMIC IONS! Generic Equatin: AX + BY AY + BX Steps fr Writing Duble-Replacement Reactins: (1) Write the cmpnents f the reactants in a skeletn equatin. Ex) Al(NO 3) 3 + H 2SO 4 (2) Identify the catins and anins in each cmpund. Ex) Al 3+ and NO 3- ; H + 2- and SO 4 (3) Pair up each catin with the anin frm the ther cmpund. Ex) Al 3+ 2- pairs with SO 4 ; H + - pairs with NO 3 (4) Write the frmulas fr the prducts using the pairs frm Step 3. Ex) Al 2(SO 4) 3 and HNO 3 (5) Write the cmplete equatin fr the duble-replacement reactin. Ex) Al(NO 3) 3 + H 2SO 4 Al 2(SO 4) 3 + HNO 3 (6) Balance the equatin. Ex) 2Al(NO 3) 3 + 3H 2SO 4 Al 2(SO 4) 3 + 6HNO 3 Duble-replacement (DR) Reactin Practice
Predicting Reactin Types Flw Chart 1) Is there a single reactant? YES Decmpsitin Reactin NO 2) Are the reactants O 2 and a hydrcarbn? YES NO Cmbustin Reactin 3) Are the reactants tw inic cmpunds? YES NO Duble Replacement Reactin 4) Are the reactants an element and cmpund? YES NO Single Replacement Reactin Synthesis Reactin
Net Inic Equatins Definitins: Net inic equatin chemical equatin which includes nly thse cmpunds left after the spectatr ins are eliminated Spectatr ins ins that shw up n bth sides f the reactin Aqueus slutin slutin which cntains ne r mre substances disslved in water Slute what is disslved Slvent what des the disslving (ften water) Steps t Writing Net Inic Equatins: (1) Make sure everything that is aqueus (aq) is written as its ins Table R-8 Slubility Guidelines n page 974 in textbk will help yu determine if smething is sluble (aq) r insluble (s) Ex) 2NaOH(aq) + CuCl 2(aq) 2NaCl(aq) + Cu(OH) 2(s) 2Na + (aq) + 2OH - (aq) + Cu 2+ (aq) + 2Cl - (aq) 2Na + (aq) + 2Cl - (aq) + Cu(OH) 2(s) This is the cmplete inic equatin (2) Cancel spectatr ins (spectatr ins dn t participate in the reactin and appear n bth sides f the equatin) Ex) 2Na + (aq) + 2OH - (aq) + Cu 2+ (aq) + 2Cl - (aq) 2Na + (aq) + 2Cl - (aq) + Cu(OH) 2(s) (3) Write net inic equatin Ex) 2OH - (aq) + Cu 2+ (aq) Cu(OH) 2(s) Ex #1: Water is frmed) HBr(aq) + NaOH(aq) H 2O(l) + NaBr(aq) Net inic equatin: H + (aq) + OH - (aq) H 2O(l) Ex #2: Gas is frmed) 2HI(aq) + Li 2S(aq) H 2S(g) + 2LiI(aq) Net inic equatin: 2H + (aq) + S 2- (aq) H 2S(g) Net Inic Equatin Practice