4 Fe + 3 O 2 2 Fe 2 O 3

Transcription

1 UNIT 7: STOICHIOMETRY NOTES (chapter 9) INTRO TO STOICHIOMETRY Reactin Stichimetry: Stichimetry is simply a way t shw f smething this is. Relatinship between a given and an unknwn: GIVEN UNKNOWN Type 1 Type 2 Type 3 Type 4 Mle Rati: (REVIEW) DEPENDS ON A BALNCED EQUATION (HINT: YOU WILL NEED TO BE ABLE TO WRITE BALANCED EQNS) Ratis between Fe and O 2: 4 Fe + 3 O 2 2 Fe 2 O 3 OR Ratis between Fe and Fe 2O 3 OR Ratis between O 2 and Fe 2O 3 OR Mlar Mass: (frm the Peridic Table) Example: Carbn = (1 ml C = ) What is the mlar mass f Al 2O 3? Al: = O: = Ttal Mlar Mass f Al 2O 3 = OR 1 mle Al 2O 3 =

2 IDEAL STOICHIOMETRY CALCULATIONS REVIEW: MOLE MOLE EXAMPLE: 4 Fe + 3 O 2 2 Fe 2O 3 Hw many mles f Fe are needed t react with 12.0 ml f O 2? PRACTICE 1: KCl + Br 2 KBr + Cl 2 Hw many mles f chlrine are prduced frm 0.37 mles f ptassium chlride? PRACTICE 2: C 3H 8 + O 2 CO 2 + H 2O Hw many mles f xygen are needed t prduce 2.04 mles f carbn dixide? MASS MASS STOICHIOMETRY CALCULATIONS PROBLEM SET-UP: MOLAR MASS (Given) MOLE RATIO MOLAR MASS (Unknwn) g GIVEN = TYPE : MASS MASS EXAMPLE PROBLEM: The reactin between hydrgen and xygen prduce 13.1 g f water. Hw many grams f xygen reacted? STEPS 1 & 2: Write and balance the equatin. STEP 3: Organize data: Determine mlar masses f given/unknwn: STEP 4: Plan Set Up & Slve: =

3 PRACTICE PROBLEMS: 1. 2 KCl + Br 2 2 KBr + Cl 2 Hw many grams f ptassium chlride are needed t prduce g f chlrine? 2. C 3H O 2 3 CO H 2O Hw many grams f xygen are needed t prduce g f carbn dixide? 3. Acetylene gas (C 2H 2) burns in the xyacetylene trch fr welding. Hw many grams f C 2H 2 are burned in xygen if the reactin prduces 75.0 g f carbn dixide? Dn t frget t balance the equatin first! C 2H 2 + O 2 CO 2 + H 2O 4. Oxygen was discvered by Jseph Priestly in 1774 when he heated mercury (II) xide t decmpse it t its cnstituent elements. Hw many grams f mercury (II) xide are needed t prduce 125 g f xygen gas? 5. Ammnium nitrate decmpses int water and laughing gas (nitrus xide N 2O), which is smetimes used as an aesthetic in dentistry. Hw many grams f ammnium nitrate are required t prduce 33.0 grams f N 2O? 6. Cnsider the reactin when cpper (II) metal is added t silver nitrate in slutin. What mass f silver is prduced frm g f cpper?

4 LIMITING REACTANTS Limiting Reactant: Excess Reactant: The amunt f the prduct is determined by S Hw d we figure ut the limiting reactant? Example: Hw many grams f aluminum sulfide can frm frm the reactin f 9.00 g f aluminum and 8.00 g f sulfur? 1. Balanced Equatin: 2. Cmplete TWO mass-mass calculatins, ne fr each reactant given: 3. The reactant that prduces the amunt f PRODUCT is the. Sulfur prduced g Al2S3; Aluminum prduced g Al2S3 Thus making the limiting reactant AND therefre, g f Al2S3 are prduced (amunt f prduct prduced is!!!) is therefre the excess reactant (ALWAYS the ther reactant). ****When yu d limiting reactant prblems, yu must slve bth mass-mass calculatins and circle nly ONE f the answers the mass that is prduced frm the limiting reactant/the ne that is the SMALLER mass. Nt circling an answer at all OR circling bth answers will result in the prblem being cunted wrng!!!

5 Practice Prblem # 1: Carbn mnxide (CO) can be cmbined with hydrgen t prduce methanl, CH 3OH. If yu had g CO and g H 2, what mass f CH 3OH culd be prduced? What is the limiting reactant? Shw all wrk! Practice Prblem #2: Ammnia, NH 3, is used thrughut the wrld as a fertilizer. T manufacture ammnia, nitrgen (N 2) is cmbined with hydrgen (H 2) in a synthesis reactin. If 92.7 g N 2 and g H 2 are used, which is the limiting reactant? What mass f ammnia is prduced? All wrk must be shwn t demnstrate hw yu came up with the answer.

6 PERCENT YIELD Terms t Knw: 1. Theretical Yield: 2. Actual Yield: Percentage Yield = X 100 In reality, actual yields are ften than theretical yields S hw d we determine percentage yield? 1. Start with a balanced chemical equatin. 2. Determine the --this will be the mass in the questin that ges with the 3. Determine the --this will be the mass in the questin that ges with the 4. Slve a, using yur given f the reactant and slving fr the 5. The answer t yur mass-mass prblem is the 6. Slve fr Example: Calcium carbnate decmpses. What is the percent yield if 60.0 grams f calcium carbnate is heated t frm 15.0 grams f calcium xide? 1. Write a balanced equatin: 2. Determine/Find the Actual Yield: : This is the actual yield because it has t be 3. Find the given fr the mass-mass calculatin t determine the theretical yield: : This is the given because it must be an

7 4. Set up a mass-mass calculatin: 5. Slve fr percent yield using frmula: Percent Yield = x 100 = Final Answer: Practice Prblem #1: What is the percentage yield in the fllwing reactin? 5.50 g f hydrgen gas reacts with nitrgen gas t frm g f ammnia (NH 3). Practice Prblem #2: In the reactin f sdium hydrxide and carbn dixide prducing sdium carbnate and water, 0.40 g f sdium hydrxide prduces 0.51 g f sdium carbnate. What is the percent yield f the reactin?