1. Chemical Quantities: Stoichiometry

2. Mole Ratios

3. Intro Analogy Let’s make some sandwiches. 2 pieces bread + 3 slices meat + 1 slice cheese  1 sandwich What if we want to make 50 sandwiches? How many ingredients would we need? 50 x entire equation 100 pieces bread + 150 slices meat + 50 slices cheese  50 sandwiches

4. Application Chemical equations are like recipes for reactions. Coefficients in a chemical equation indicate the relative number of particles of each substance taking part in a reaction.

5. Application CO(g) + 2H 2 (g)  CH 3 OH(l) If we multiplied the equation by 12 it would still be balanced. 12CO(g) + 24H 2 (g)  12CH 3 OH(l) Because 12 = 1 dozen we can now read the coefficients as dozens. 1 dozen CO(g) + 2 dozen H 2 (g)  1 dozen CH 3 OH(l)

6. Application We could also multiply the original balanced equation by 6.02 x 10 23. (6.02 x 10 23 )CO(g) + (1.204 x 10 24 )H 2 (g)  (6.02 x 10 23 ) CH 3 OH(l) Because 6.02 x 10 23 = 1 mole, we can now read the coefficients as moles. 1 mol CO(g) + 2 mol H 2 (g)  1 mol CH 3 OH(l)

7. Application Coefficients in a balanced chemical equation give a ratio of the # of molecules, the # of moles, or even the # of dozens present in the reaction. We will focus on the mole relationships that balanced chemical equations provide.

8. Stoichiometry The study of the quantitative, or measurable, relationships that exist in chemical formulas and chemical reactions. In order to successfully complete stoichiometry problems you must understand mole relationships.

9. Stoichiometry: Relating Moles to Molecules Propane (C 3 H 8 ) is a fuel commonly used for cooking on gas grills and for heating in rural areas where natural gas is unavailable. Propane reacts with oxygen gas to produce heat and the products carbon dioxide and water. Give the balanced equation for this reaction and state the meaning of the equation in terms of numbers of molecules and moles of molecules.

10. Stoichiometry: Relating Moles to Molecules C 3 H 8 + 5O 2  3CO 2 + 4H 2 O Molecules: 1 molecule C 3 H 8 + 5 molecules O 2  3 molecules CO 2 + 4 molecule H 2 O Moles: 1 mole C 3 H 8 + 5 moles O 2  3 moles CO 2 + 4 moles H 2 O

11. Stoichiometry: Using Mole Relationships A mole ratio is the ratio of moles of one substance to moles of another substance in a balanced chemical equation. Mole ratios can be used to convert the number of moles of one substance in a reaction to the number of moles of another substance.

12. Mole Analogy For every 3 school buses that arrive at school, 2 will transport marching band members and 1 will transport choir members. 3 buses  2 marching band + 1 choir If 12 buses show up to school, how many will transport choir members?

13. Mole Analogy 3 buses  2 marching band + 1 choir 12 buses x 4 of the 12 buses will carry choir members The ratio becomes your conversion factor. 3 buses 1 choir = 4 choir

14. Mole Ratios What is the mole ratio of water to oxygen when water decomposes? What is the mole ratio of water to hydrogen in the reaction? 2H 2 O(l)  2H 2 (g) + O 2 (g) 2 mol H 2 O : 1 mol O 2 2 mol H 2 O : 2 mol H 2 = 1:1

15. Stoichiometry: Using Mole Ratios What number of moles of O 2 will be produced by the decomposition of 5.8 moles of water? Given: 5.8 mol H 2 O Unknown: moles of O 2 5.8 mol H 2 O  ? moles of O 2

16. Stoichiometry: Using Mole Ratios 2H 2 O(l)  2H 2 (g) + O 2 (g) 5.8 mol H 2 O x If 5.8 mol of water decompose, 2.9 mol of oxygen gas will be produced. 2 mol H 2 O 1 mol O 2 = 2.9 mol O 2

17. Mole-Mole Practice Problem 1 Methane (CH 4 ) burns in oxygen to form carbon dioxide and water. (a) How many moles of oxygen gas are required to react with 7.4 moles of methane? (b) How many moles of carbon dioxide gas will be produced by reacting 2.6 moles of oxygen with excess methane?

18. CH 4 (g) + 2O 2  CO 2 (g) + 2H 2 O(g) (a) How many moles of oxygen gas are required to react with 7.4 moles of methane? 7.4 mol CH 4  ? mol O 2 7.4 mol CH 4 x = 14.8 mol O 2 1 mol CH 4 2 mol O 2

19. CH 4 (g) + 2O 2  CO 2 (g) + 2H 2 O(g) (b) How many moles of carbon dioxide gas will be produced by reacting 2.6 moles of oxygen with excess methane? 2.6 mol O 2  ? mol CO 2 2.6 mol O 2 x = 1.3 mol CO 2 1 mol CO 2 2 mol O 2

20. Stoichiometry Problems

21. Mole ratios (from the coefficients in a balanced chemical equation) allow us to convert moles of one substance in a chemical reaction to moles of another substance in the reaction. We learned last semester that we can convert the mass of a substance to moles of that substance. By combining the two processes, we can convert quantities of one substance to quantities of another.

22. Mass-Mass Problems Mass of one substance is given and you are asked to find the mass of another substance. 1. Convert mass of given to moles of given (using molar mass). 2. Convert moles of given to moles of unknown (using the mole ratio). 3. Convert moles of unknown to mass of unknown (using molar mass).

23. Mass-Mass Practice Solid lithium hydroxide has been used in space vehicles to remove exhaled carbon dioxide from the living environment. This produces solid lithium carbonate and liquid water. What mass of carbon dioxide can 1.00 x 10 3 g of lithium hydroxide absorb?

24. Mass-Mass Practice Hydrofluoric acid, an aqueous solution containing dissolved hydrogen fluoride, is used to etch glass by reacting with the silica, SiO 2, in the glass to produce gaseous silicon tetrafluoride and liquid water. (a) Calculate the mass of hydrogen fluoride needed to react with 5.68 g of silica. (b) Calculate the mass of water produced by the reaction in part a.

25. Further Applications How would you convert a given number of particles of a substance to the mass of another substance? How would you convert the moles of a given substance to the mass of another substance?

26. Summary Mass of Given Moles of Given Moles of Unknown Mass of Unknown use molar mass use mole ratio use molar mass