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STOICHIOMETRY

STOICHIOMETRY. Chemistry I – Chapter 12. (1-2-3) General Approach For Problem Solving:. 1. Clearly identify the Goal or Goals and the UNITS involved. (What are you trying to do?). 2. Determine what is given and the UNITS.

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STOICHIOMETRY

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  1. STOICHIOMETRY Chemistry I – Chapter 12

  2. (1-2-3) General Approach For Problem Solving: 1. Clearly identify the Goal or Goals and the UNITS involved. (What are you trying to do?) 2. Determine what is given and the UNITS. 3. Use conversion factors (which are really ratios) and their UNITS to CONVERT what is given into what is desired.

  3. Sample problem for general problem solving. Sam has entered into a 10 mile marathon. Use ALL of the following conversions (ratios) to determine how many inches there are in the race. 5280 ft = 1 mile; 12 inches = 1 ft 1. What is the goal and what units are needed? Goal = ______ inches 2. What is given and its units? 10 miles Units match 3. Convert using factors (ratios). 10 miles = inches 633600 Goal Given Convert Menu

  4. Converting grams to moles. Determine how many moles there are in 5.17 grams of Fe(C5H5)2. Given Goal units match 5.17 g Fe(C5H5)2 = moles Fe(C5H5)2 0.0278 Use the molar mass to convert grams to moles. Fe(C5H5)2 2 x 5 x 1.001 = 10.01 2 x 5 x 12.011 = 120.11 1 x 55.85 = 55.85

  5. Stoichiometry (more working with ratios) Ratios are found within a chemical equation. 2HCl + Ba(OH)2 2H2O + BaCl2 1 1 coefficients give MOLAR RATIOS 2 moles of HCl react with 1 mole of Ba(OH)2 to form 2 moles of H2O and 1 mole of BaCl2

  6. Mole – Mole Conversions When N2O5 is heated, it decomposes: 2N2O5(g) 4NO2(g) + O2(g) a. How many moles of NO2 can be produced from 4.3 moles of N2O5? 2N2O5(g) 4NO2(g) + O2(g) 4.3 mol ? mol Units match 4.3 mol N2O5 = moles NO2 8.6 b. How many moles of O2 can be produced from 4.3 moles of N2O5? 2N2O5(g) 4NO2(g) + O2(g) 4.3 mol ? mol 4.3 mol N2O5 = mole O2 2.2

  7. gram ↔ mole and gram ↔ gram conversions When N2O5 is heated, it decomposes: 2N2O5(g) 4NO2(g) + O2(g) a. How many moles of N2O5 were used if 210g of NO2 were produced? 2N2O5(g) 4NO2(g) + O2(g) ? moles 210g Units match 210 g NO2 = moles N2O5 2.28 b. How many grams of N2O5 are needed to produce 75.0 grams of O2? 2N2O5(g) 4NO2(g) + O2(g) 75.0 g ? grams 75.0 g O2 = grams N2O5 506

  8. Gram to Gram Conversions Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq)  AlCl3(aq) + H2(g) 2 6 2 3 First write a balanced equation.

  9. Gram to Gram Conversions Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq)  AlCl3(aq) + H2(g) 2 6 2 3 ? grams 3.45 g Now let’s get organized. Write the information below the substances.

  10. gram to gram conversions Aluminum is an active metal that when placed in hydrochloric acid produces hydrogen gas and aluminum chloride. How many grams of aluminum chloride can be produced when 3.45 grams of aluminum are reacted with an excess of hydrochloric acid? Al(s) + HCl(aq)  AlCl3(aq) + H2(g) 2 6 2 3 ? grams 3.45 g Units match 3.45 g Al = g AlCl3 17.0 Let’s work the problem. We must always convert to moles. Now use the molar ratio. Now use the molar mass to convert to grams.

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