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Chapter 12. Stoichiometry u Greek for measuring elements u The calculations of quantities in chemical reactions based on a balanced equation. u We can.

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Presentation on theme: "Chapter 12. Stoichiometry u Greek for measuring elements u The calculations of quantities in chemical reactions based on a balanced equation. u We can."— Presentation transcript:

1 Chapter 12

2 Stoichiometry u Greek for measuring elements u The calculations of quantities in chemical reactions based on a balanced equation. u We can interpret balanced chemical equations several ways.

3 In terms of Particles u Atom - Element u Molecule Molecular compound (non- metals) or diatomic (O 2 etc.) u Formula unit Ionic Compounds (Metal and non- metal)

4 2H 2 + O 2 2H 2 O u Two molecules of hydrogen and one molecule of oxygen form two molecules of water.

5 Look at it differently 2H 2 + O 2 2H 2 O u 2 dozen molecules of hydrogen and 1 dozen molecules of oxygen form 2 dozen molecules of water.

6 Look at it differently 2H 2 + O 2 2H 2 O u 2 x (6.02 x 10 23 ) molecules of hydrogen and 1 x (6.02 x 10 23 ) molecules of oxygen form 2 x (6.02 x 10 23 ) molecules of water.

7 Look at it differently 2H 2 + O 2 2H 2 O u 2 moles of hydrogen and 1 mole of oxygen form 2 moles of water.

8 In terms of Moles 2 Al 2 O 3 Al + 3O 2 u The coefficients tell us how many moles of each kind of particle

9 In terms of mass u The law of conservation of mass applies u We can check using moles 2H 2 + O 2 2H 2 O

10 Your turn Show that the following equation follows the Law of conservation of mass: 2 Al 2 O 3 4Al + 3O 2

11 Mole to mole conversions 2 Al 2 O 3 Al + 3O 2 every time we use 2 moles of Al 2 O 3 we make 3 moles of O 2 2 moles Al 2 O 3 3 mole O 2 or 2 moles Al 2 O 3 3 mole O 2

12 Mole to Mole conversions u How many moles of O 2 are produced when 3.34 moles of Al 2 O 3 decomposes? 2 Al 2 O 3 Al + 3O 2 3.34 moles Al 2 O 3 2 moles Al 2 O 3 3 mole O 2 =5.01 moles O 2

13 Your Turn 2C 2 H 2 + 5 O 2 4CO 2 + 2 H 2 O u If 3.84 moles of C 2 H 2 are burned, how many moles of O 2 are needed? u How many moles of C 2 H 2 are needed to produce 8.95 mole of H 2 O?

14 Mass in Chemical Reactions How much do you make? How much do you need?

15 We cant measure moles!! u What can we do? convert grams to moles use moles to change chemicals quantities Balance the equation Convert the moles back to grams

16 Periodic Table Mole sA Mole sB Mass g B Periodic Table Balanced Equation Mass g A Decide where to start based on the units you are given Stop based on what unit you are asked for

17 Conversions 2C 2 H 2 + 5 O 2 4CO 2 + 2 H 2 O u How many moles of C 2 H 2 are needed to produce 8.95 g of H 2 O? u If 2.47 moles of C 2 H 2 are burned, how many g of CO 2 are formed?

18 More examples… u If 10.1 g of Fe are added to a solution of Copper (II) Sulfate, how much solid copper would form? Fe + CuSO 4 Fe 2 (SO 4 ) 3 + Cu 2Fe + 3CuSO 4 Fe 2 (SO 4 ) 3 + 3Cu 10.1 g Fe 55.85 g Fe 1 mol Fe 2 mol Fe 3 mol Cu 1 mol Cu 63.55 g Cu =17.3 g Cu

19 More Examples u Silicon for computer chips are created using this reaction: SiCl 4 + 2Mg 2MgCl 2 + Si u MgCl 2 is the byproduct of this reaction. u How many grams of MgCl 2 are produced along with 9.3 g of silicon?

20 For Example u The U. S. Space Shuttle boosters use this reaction: 3 Al(s) + 3 NH 4 ClO 4 Al 2 O 3 + AlCl 3 + 3 NO + 6H 2 O u How much Al must be used to react with 652 g of NH 4 ClO 4 ? u How much water (in grams) is produced? u How much AlCl 3 ?

21 How do you get good at this?

22 Gases and Reactions

23 We can also change u Liters of a gas to moles u At STP u 0ºC and 1 atmosphere pressure u At STP 22.4 L of a gas = 1 mole u If 6.45 moles of water are decomposed, how many liters of oxygen will be produced at STP?

24 For Example u If 6.45 grams of water are decomposed, how many liters of oxygen will be produced at STP? 2H 2 O 2H 2 + O 2 6.45 g H 2 O 18.02 g H 2 O 1 mol H 2 O 2 mol H 2 O 1 mol O 2 22.4 L O 2

25 Your Turn u How many liters of CO 2 at STP will be produced from the complete combustion of 23.2 g C 4 H 10 ? u What volume of oxygen will be required?

26 Limiting Reagent u If you are given one dozen loaves of bread, a gallon of mustard and three pieces of salami, how many salami sandwiches can you make? u The limiting reagent is the reactant you run out of first. u The excess reagent is the one you have left over. u The limiting reagent determines how much product you can make

27 How do you find out? u Do two stoichiometry problems. u The one that makes the least product is the limiting reagent. u For example u Copper reacts with sulfur to form copper ( I ) sulfide. If 10.6 g of copper reacts with 3.83 g S how much product will be formed?

28 u If 10.6 g of copper reacts with 3.83 g S. How many grams of product will be formed? 2Cu + S Cu 2 S 10.6 g Cu 63.55g Cu 1 mol Cu 2 mol Cu 1 mol Cu 2 S 1 mol Cu 2 S 159.16 g Cu 2 S = 13.3 g Cu 2 S 3.83 g S 32.06g S 1 mol S 1 S 1 Cu 2 S 1 mol Cu 2 S 159.16 g Cu 2 S = 19.0 g Cu 2 S = 13.3 g Cu 2 S


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