Mathematics of Chemical Equations

1. Mathematics of Chemical Equations

2. Methanol is starting material for some jet fuels.

3. early chemists did not care much about measurements, they cared more about observations and the things that they could get from a chemical reaction 1. Who was one of the first scientists to actually measure the reactants and the products? • Lavoisier

4. calculations made from these measurements help us to see relationships in chem rxns and to truly understand chem changes • it helps us control chem rxns in industries • it helps us to calculate the exact quantities of the substances in the rxn and predict the amnt of each product--this is imminently practical

5. 2. Why is this so practical, especially when we mention the word "Money"? • Industries seek to make a maximum amount of product while using a minimum amount of reactants

6. coefficients found in chemical rxns can tell us three things • 3. What are these three things? 1. Mole Ratio 2. Molecule Ratio 3. Liter Ratio

7. Objective 1 • If given the mole amount of one of the reactants or products, be able to determine the mole amounts of all other products and reactants

8. now that we know this and we can still do some stoichiometry lets have some fun Ex. 1 What number of moles of O2 will be produced by the decomposition of 5.98 mol of water? Ex. 2 Calculate the number of moles of oxygen gas required to react exactly with the combustion of 4.30 mol of propane, C3H8

9. Propane is often used as a fuel for outdoor grills.

10. Objective 2 • If given the mass amount of one of the reactants or products, be able to determine the mass amounts of all other products and reactants

11. coefficients can help you calculate the masses of the reactants and products • Remember: coefficients do not tell you the relative masses; BUT, they can tell you the relative moles, and where there is a mole they is a way!

12. Let us the learn the THINK EQUAS THINK use equation to convert moles of given to moles of needed Convert moles of needed to units of needed Convert given to moles

13. Ex. 3 Propane, C3H8, when used as a fuel, combusts with oxygen gas. What mass of oxygen gas will be required to react exactly with 96.1 g of propane? Calculate the mass of water formed?

14. Ex. 4 Baking Soda, NaHCO3, is often used as an antacid. It neutralizes excess hydrochloric acid secreted by the stomach. Milk of magnesia, which is an aqueous suspension of magnesium hydroxide, is also used as an antacid. Which antacid can consume the most stomach acid. 1.00 g of NaHCO3 or 1.00 g of Mg(OH)2?

15. ` Ex. 5 Silver nitrate solution reacts with Sodium chloride solution. How much solid will be formed if you have 25.0 g of Silver nitrate in the solution?

16. Read Chemistry in Focus on Page 257 for qiuz tomorrow.

17. Objective 3 • If given the amounts of the reactants used, be able to determine the maximum amounts of products that will be produced along with which reactant is the limiting reactant.

18. chemical engineers are extremely concerned with producing the greatest amnt of product for the least amnt of money • 4. What does this mean to them? • Less waste means more money saved!!

19. the less expensive reactant is usually added in large amnts • the reactant that is all used up is called the limiting reactant. • 5. Why called "limiting"?

20. http://www.youtube.com/watch?v=qJ-qMbhtLHk&feature=related

21. 6. Write a good analogy of this principle?

22. Steps to Success 1. Convert the amount of 1st reactant to g(of solids or liquids) or L(of gases) of one of the products using Think Equas Think 2. Repeat for the second reactant-convert to the same product 3. Compare-the one that gives you the most product-that REACTANT is in INXS-do not use it! The one that gives you the least product is your LR.

23. 4. Use the LR to find the second product using T-E-T 5. Divide the amnt of product formed by the LR by the amount formed by the INXS-to get the % efficiency 6. Subtract % efficiency from 100 to get % wasted 7. Multiply the decimal version of the % wasted into the original amnt of INXS to get the INXS wasted

24. Ex. 6 Suppose 25.0 kg of nitrogen gas and 5.00 kg of hydrogen gas are mixed and reacted to form ammonia. Calculate the mass of ammonia produced when this reaction is run to completion

25. Farmer Rodney Donala looks out over his corn fields in front of his 30,000-gallon tank (at right) of anhydrous ammonia, a liquid fertilizer.

26. Ex. 7 Nitrogen gas can be prepared by passing gaseous ammonia over solid cupric oxide at high temperatures. The other products of the reaction are solid copper and water vapor. How many grams of N2 are formed when 18.1 g of NH3 are reacted with 90.4 of CuO?

27. Copper (II) oxide reacting with ammonia in a heated tube.

28. Objective 4 • If actual amount of product is given, be able to determine the theoretical yield and its percent yield

29. 7. We just figured how to determine, theoretically(“on paper”) how much product should be formed, will that exact amount be produced in real life? 8. Why not?

30. 9. What is percent yield? • Comparison between what should have been produced and what was produced • (Actual/ Theoretical) x 100 = percent yield

31. Ex. 8 Methanol can be produced by the reaction between carbon monoxide and hydrogen. Suppose 69.5 kg of CO(g) is reacted with 8.60 kg of H2. • Calculate the theoretical yield • If 35,700 g of CH3OH is actually produced, what is the percent yield of methanol?