StoichiometryChapter 11

STOICHIOMETRY1. The quantitative relationship between

reactants and products in a chemical reaction.

2. Calculation of the quantities of reactants and products in a chemical reaction.

Predicting Product Amounts

Suppose we are going to react copper with silver nitrate to produce silver. The reaction is:

Cu(s) + AgNO3 (aq) Cu(NO3)2 (aq) + Ag (s)

First you must balance the reaction.

Predicting Product Amounts

Cu(s) + 2 AgNO3 (aq) Cu(NO3)2 (aq) + 2 Ag (s)

If you had 1.00 moles of Cu, how many moles of Ag would you produce? 2 moles Ag

If you had 1.00 moles of Cu, how many grams of Ag would you produce? 2mol x (107.870 g/mol)= 215.74 g

Predicting Product Amounts

If you reacted 127 grams of copper in a solution of silver nitrate, how many grams of silver would you produce?127g ÷ 63.54 g/mol = 1.99 moles Cu1.99 moles Cu x 2 moles Ag = 3.99 moles Ag

1 mole Cu3.99 moles Ag x 107.87 g/mol = 431.21 g Ag

STOICHIOMETRYProcess

1. Read the problem. 2. Identify the known and unknown.3. Write the chemical equation.4. Balance the chemical equation.5. Do the math.

STOICHIOMETRY Flow Chart

Given Moles of Given Moles of Unknown Desired Unit.

Problems1. What mass of water is created when 100.0

grams of methane gas is burned in air?CH4 + 2 O2 CO2 + 2 H2O

100 g ÷ 16.04 g/mol = 1,604.3 mol CH4

1,604.3 mol CH4 x 2 mol H2O = 3,208.6 mol H2O 1 mol CH4

2. What mass of carbon dioxide is formed?1,204.3 mol CH4 x 1 mol CO2 = 1,204.3 mol CO2

1 mol CH41,204.3 mol CO2 x 44.01 g/mol = 5.3 x 104 g CO2

3. What mass of oxygen gas was consumed?1,204.3 mol CH4 x 1 mol O2 = 1,204.3 mol O2

1 mol CH41,204.3 mol O2 x 32.0 g/mol = 3.85 x 104 g O2

4)What mass of bromine, Br2(l), reacts with water giving 13.0 g of hypobromous acid, HOBr(aq) and hydrobromic acid, HBr(aq)?

5) Find the mass of potassium carbonate, K2CO3 ,that

reacts with 65.3 g Aluminum Chloride, AlCl3. The reaction occurs in water solution.

Find the mass of the precipitate.

Write the ionic and net ionic reaction.

6)What mass of nitrogen, N2(g), reacts with 5.60 g of hydrogen, H2(g), giving ammonia, NH3?

N2 + 3 H22 NH3

5.60 g H2 x 1 mol H2 x 1 mol N2 x 28.02 g N2 = 25.9 g 2.016 g 3 mol H2 1 mol N2

What mass of ammonia forms?31.53 g NH3

Dealing with VolumesBecause volumes are easier to measure than mass when

dealing with gases, the last problem could have been:

At STP, what volume of nitrogen, N2(g), reacts with 62.1 L of hydrogen, H2(g), giving ammonia, NH3? N2 + 3 H22 NH362.1 L H2 x 2 vol NH3=

3 vol H2What volume of ammonia forms?

41.4 L NH3

7)What mass of sodium, Na, reacts in water to produce 8.13 liters of H2 at STP. The other product is sodium hydroxide, NaOH.2 Na +2 H2O 2 NaOH + H2

8.13 L H2 x 2 vol Na x 1mol x 22.991 g = 16.7 g 1 mol H2 22.4 L 1 mol Na

8)1.93x1025 molecules of NH3(g) burns in air to produce nitrogen dioxide gas and water vapor. What volume of nitrogen dioxide forms at STP?

4 NH3 + 7 O2 4 NO2 + 6 H2O1.93x1025 molecules NH3 x 1 mol = 32.06

6.02 x 1023 molecules

32.6 mol NH3 x 22.4 L x 4 vol NO2 =730 L NO2

1 mol 4 vol NH3

9) 3.16 liters of C3H8(g) reacts in air to form carbon dioxide and water. C3H8 + 5 O2 3 CO2 + 4 H2O

a. What volume of oxygen is reacting at STP? 3.16 L x 5 vol O2 = 15.8 L 1 vol C3H8

b. What mass of water forms?3.16 L x 4 vol H2O x 1 mol x 18.02 g = 227 g

1 vol C3H8 22.4 L 1 mol

10. Calcium reacts in water to form calcium hydroxide, Ca(OH)2, and hydrogen, H2. What volume of hydrogen forms at STP if 8.02 g of Ca react in excess water?

11. Hydrogen, H2, reacts with sulfur, S8, to form hydrogen sulfide, H2S. How many molecules of S8 reacts with 10.4 liters of H2?

12. What mass of BaCl2 reacts with 54.5 g of K3PO4?

The reaction is:

BaCl2(aq) + K3PO4(aq) Ba3(PO4)2(s) + KCl(aq)

13. What mass of potassium chlorate, KClO3, decomposes into potassium chloride, KCl, and 13.6 liters of oxygen, O2?

14. How many molecules of C4H10 react with 42.0 g of oxygen, O2? What volume of carbon dioxide forms?

15. How many moles of sulfur dioxide, SO2, form when 3.0 moles of S8 reacts with ozone, O3?

16. What mass of phosphoric acid, H3PO4, reacts with 460.0 g of KOH? The products are potassium phosphate, K3PO4, and water.

How Do Hot Fudge Sundaes and Limiting Reactants Relate?

How Many Sundaes Can You Make?

Two!

The chocolate syrup limits the recipe!

• Which reactant remains when 6.70 mole H2 reacts with 3.20 moles of N2

• 3 H2 + N22 NH3

Which reactant is the limiting reactant?

Step 1

Moles of reactant

Moles of product

Moles of H2 Mole Ratio Moles of NaCl6.70 moles of H2 2 mol NH3 = 4.47 mol NH3

3 mol H2

3 H2 + N22 NH3

Moles of N2 Mole Ratio Moles of Product3.20 moles of N2 2 mol NH3 = 6.40 mol NH3

1 mol N2

Step 1

Step 1

H2 is the Limiting Reactant!

LIMITING REACTANTIf 5.0 moles of hydrogen (H2) and 5.0 moles of

oxygen (O2) are mixed and allowed to react to form water, how many moles of water could be formed?

2 H2 + O2 2 H2O

5.0 mol H2 x 2 mol H2O = 5.0 mol H2O 2 mol H2

5.0 mol O2 x 2 mol H2O = 10.0 mol H2O 1 mol O2

LIMITING REACTANTIf 10.0 grams of hydrogen (H2) and 160.0 grams

of oxygen (O2) are mixed and allowed to react to form water, what mass of water could be formed?

This is a limiting reactant problem.10.0 g H2 x 2 mol H2O x 18.02 g = 89.7 g H2O 2.02 g/mol 2 mol H2 1 mol H2O160.0 g O2 x 2 mol H2O x 18.02 g = 180.2 g H2O 32.0 g/mol 1 mol O2 1 mol H2O

LIMITING REACTANT1. Determine the mass of one reactant needed to

completely react with the other reactant. Use stoichiometry to solve.

2. Compare the mass of the ‘other’ reactant to what is actually provided and determine the limiting reactant.

3. Determine the maximum yield of the product. Use stoichiometry to solve.

PERCENT YIELD% YIELD = ACTUAL YIELD . 100%

MAXIMUM YIELD

2H2(g) + O2(g) 2H2O(l)

5.0 g of H2 and 42 g O2 are placed in a sealed box and reacted.

A. Find the limiting reactant. B. Determine the maximum yield of

H2O.

C. If 38.6 g of water form, what is the percent yield?

EXAMPLE20.0 g of Ca are placed with 20.0 g of water.

What is the limiting reactant and the maximum yield of Ca(OH)2 that forms in grams? Ca(s) + 2H2O(l) Ca(OH)2(s) + H2(g)

What if 32.0 grams of Ca(OH)2 form, what is the percent yield?

EXAMPLE10.0 g of CH4 are placed with 20.0 g of oxygen.

What is the limiting reactant and maximum yield of water in grams? CH4(g) + 2O2(g) CO2(g) + 2H2O(l)

If 10.9 grams of water form, what is the percent yield?

2. 17.38 g of manganese dioxide, MnO2, reacts in excess hydrochloric acid, HCl. The reaction is:

4HCl(aq)+MnO2(s)MnCl2(s)+2H2O(l)+Cl2(g)

a. What is the maximum yield of Cl2 in liters at STP?

b. If the actual yield of Cl2 is 4.00 liters at STP, what is the % yield?

1. 24.8 g of Calcium carbonate is decomposed as shown in the equation:

CaCO3(s) CaO(s) + CO2(g)a. What is the maximum yield of CaO that can

be produced?b. If the actual yield is 13.1 grams of CaO, what

is the percent yield?

Problems1) What volume of CO2(g) at STP is produced if 1

gallon of gasoline, C8H18, burns in air? (1.00 gallon is 3.79 liters). The density of gasoline is .7025g/ml.

2) What mass of water forms?