Stoichiometry. Goal. Calculate quantities of reactants and products needed in chemical rxns using balanced chemical equations.

Transcription

1 Chapter 12

2 Stoichiometry Goal Calculate quantities of reactants and products needed in chemical rxns using balanced chemical equations.

3 Using an Equation as a Recipe Ingredients: Frame, Seat, Wheels, Handlebar, Pedals Balanced equation: 1F + 1S + 2W + 1H + 2P 1 FSW 2 HP 2

4 How many pedals are needed to make 128 bicycles? 128 FSW 2 HP 2 2P 1 FSW2HP2 = 256 pedals 1F + 1S + 2W + 1H + 2P 1 FSW 2 HP 2

5 Examining a Balanced Chemical Equation 2H 2 S(g) + 3O 2 (g) 2SO 2 (g) + 2H 2 O(g) 2 moles of H 2 S reacts with 3 moles of O 2 to produce 2 moles of SO 2 and 2 moles of H 2 O. 4 moles of H 2 S reacts with moles 6 of O moles of O 2 are needed to produce 7 moles of H 2 O How to solve these is on the next slide.

6 Mole-Mole Ratio Problems 4 mol H 2 S 3 mole O 2 2 mol H 2 S = 6 mol O 2 7mol H 2 O 3 mole O 2 2 mol H 2 O = 10.5 mol O 2 The mol-mol ratio comes from the coefficients in the balanced equation. In the balance equation, O 2 has a coefficient of 3, H 2 O has a coefficient of 2, and H 2 S has a coefficient of 2.

7 Mass-Mass Calculation Write the balanced chemical equation Label above the equation what you are given and what you are trying to find. Convert grams of your given to moles using molar mass Multiply by the mole-mole ratio from the balanced chemical equation Convert moles of unknown to grams

8 Bringing It All Together How many grams of ammonia ( NH 3 ) should be produced when 6.00g nitrogen react with excess hydrogen? Solve: Write the balanced equation with the information labeled above it g excess? g N 2 + 3H 2 2 NH 3

9 Bringing It All Together Convert given to moles: 6.00g N 2 1 mole N 2 28 g N 2 = mol N 2 Multiply by the mole ratio: mol N 2 1 mol N2 2 mol NH 3 = mol NH 3

10 Wrapping It Up Convert moles of unknown to grams: mol NH 3 17g NH 3 1 mol NH 3 = 7.28g NH 3 Summary: When 6.00g of nitrogen(n 2 ) reacts with an excess of Hydrogen (H 2 ), 7.28g of ammonia (NH 3 ) should be produced.

11 Now You Try! What mass of aluminum is required to completely react with 7.80g oxygen in a synthesis reaction?

12 Write the balanced equation 4Al + 3O 2 2Al 2 O 3

13 Label your given and unknown information 7.80 g Since you were not given info about this compound, don t worry about it and don t use it. 4Al + 3O 2 2Al 2 O 3

14 NEXT?... Convert given to moles: 7.80g O 2 1 mol O 2 = 0.244mol O2 32g O 2 Multiply by the mole ratio: 0.244mol O 2 4 mol Al 3 mol O 2 = mol Al

15 AND FINALLY!! Convert moles of unknown to grams: mol Al 27g Al 1 mol Al = 8.78g Al 8.78g of aluminum (Al) should be required to react completely with7.80g of oxygen (O 2 ) in the synthesis of aluminum oxide (Al 2 O 3 ).

16 Mass-Volume Calculation Write the balanced chemical equation Label above the equation what you are given and what you are trying to find. Convert grams of your given to moles using molar mass Multiply by the mole-mole ratio from the balanced chemical equation Convert moles of unknown to liters (a.k.a dm 3 ) using molar volume (22.4L/ 1mol)

17 Bringing It All Together How many liters of oxygen are necessary for the combustion of 134g of magnesium, assuming the reactions occurs at STP? Solve: Write the balanced equation with the information labeled above it. 134 g? L 2Mg + O 2 2 MgO

18 Bringing It All Together Convert given to moles: 134g Mg 1 mole Mg 24.3 g Mg Multiply by the mole ratio: = mol Mg mol Mg 1 mol O 2 2 mol Mg = mol O 2

19 Wrapping It Up Convert moles of unknown to liters: molo LO 2 1 mol O 2 = 61.8 L O L of O 2 are required to completely combust 134g Mg in the synthesis of MgO.

20 Volume-Mass Calculation Write the balanced chemical equation Label above the equation what you are given and what you are trying to find. Convert liters of your given to moles using molar volume Multiply by the mole-mole ratio from the balanced chemical equation Convert moles of unknown to grams using molar mass

21 Bringing It All Together Find the mass of sulfur (S 8 ) required to react with oxygen to produce 2.47L of sulfur dioxide gas at STP. Solve: Write the balanced equation with the information labeled above it.? g 2.47L S O 2 8 SO 2

22 Bringing It All Together Convert given to moles: 2.47L SO 2 1 mole SO L SO 2 = mol SO 2 Multiply by the mole ratio: mol SO 2 1 mol S 8 8 mol SO2 = mol S 8

23 Wrapping It Up Convert moles of unknown to grams: mol S 8 256g S 8 1 mol S 8 = 3.53 g S g of sulfur (S 8 ) are required to produce 2.47 L of sulfur dioxide (SO 2 ).

24 Volume-Volume Calculations Write the balanced chemical equation Label above the equation what you are given and what you are trying to find. Convert liters of your given to moles using molar volume (22.4L/1mol) Multiply by the mole-mole ratio from the balanced chemical equation Convert moles of unknown to liters using molar volume (22.4L/1 mol)

25 Bringing It All Together What volume of H 2 S gas is needed to produce 14.2 L of water at STP? Solve: Write the balanced equation with the information labeled above it.?l 14.2L 2H 2 S + 3O 2 2 SO H 2 O

26 Bringing It All Together Convert given to moles: 14.2 L H 2 O 1 mole H 2 O 22.4 L H 2 O Multiply by the mole ratio: = mol H 2 O mol H 2 O 2 mol H 2 S 2mol H 2 O = mol H 2 S

27 Wrapping It Up Convert moles of unknown to liters: mol H 2 S 22.4 LH 2 S 1 mol H 2 S = 14.2 L H 2 S 14.2 L of H 2 S are required to produce 14.2 L H 2 O.