Chemical Quantities: Stoichiometry. UNIT 4: Ch. 12 Ms. Kiely, Coral Gables Senior High

Transcription

1 Chemical Quantities: Stoichiometry UNIT 4: Ch. 12 Ms. Kiely, Coral Gables Senior High 1

2 BELL RINGER How many moles are in 62.0g of hydrogen gas?

3 ANSWER How many moles are in 62.0g of hydrogen gas? 30.7 mol

4 The term stoichiometry describes the relationships between reactants and products during chemical reactions. For instance, understanding how much of a reactant is needed to make a particular amount of something, or figuring out how much of your product(s) will be formed based on the amount of reactant(s) that you have. It is just like figuring out the perfect recipe! Except instead of this being a recipe for food it is a recipe for a chemical reaction.

5 PRACTICE How much water is yielded when 62.0g of hydrogen reacts with an excess of oxygen gas? 2H₂(g) + O₂(g) 2H₂O(g)

6 ANSWER How much water is yielded when 62.0g of hydrogen reacts with an excess of oxygen gas? 2H₂(g) + O₂(g) 2H₂O(g) 553 grams

7 LIMITING & EXCESS REACTANTS Imagine that you are following a recipe to make 12 cookies. It calls for you to mix 2 eggs with 4 cups of flour. You notice that you only have 1 egg, and realize that this means you will only end up using 2 out of the 4 cups of flour, and will end up producing 6 cookies. The number of eggs limited the amount of cookies produced.

8 We can refer to the egg in our situation as the Limiting Reactant and the flour as the Excess Reactant. The cookies would, of course, be the product. -Limiting reactant: the reactant in a chemical reaction that will determine how much of the product(s) will yield, i.e. the two eggs -Excess reactant: the reactant that will not be fully used since there is a limiting reactant, meaning there will be an excess of this reactant remaining, i.e. the flour

9 PRACTICE How much water is yielded when 62.0 g of hydrogen reacts with 32.1 g of oxygen? 2H₂(g) + O₂(g) 2H₂O(g)

10 ANSWER How much water is yielded when 62.0 g of hydrogen reacts with 32.1 g of oxygen? 2H₂(g) + O₂(g) 2H₂O(g) The limiting reactant is oxygen grams of water are yielded when all of the oxygen gas (the limiting reactant) reacts with the hydrogen gas (the excess reactant).

11 PRACTICE Lithium hydroxide reacts with carbon dioxide as follows. 2LiOH + CO₂ Li₂CO₃ + H₂O What mass of lithium hydroxide is needed to react with 11g of carbon dioxide? A. 6 B. 12 C. 24 D. 48

12 ANSWER Lithium hydroxide reacts with carbon dioxide as follows. 2LiOH + CO₂ Li₂CO₃ + H₂O What mass of lithium hydroxide is needed to react with 11g of carbon dioxide? A. 6 B. 12 C. 24 D. 48

13 PRACTICE How much ammonia (NH3) is yielded when g of nitrogen react with 32.1 g of hydrogen?

14 ANSWER How much ammonia (NH3) is yielded when g of nitrogen react with 32.1 g of hydrogen? The balanced equation is: N2 + 3H2 2NH3 Hydrogen is the limiting reactant. 181 grams of ammonia

15 PRACTICE Consider the following reaction. N₂(g) + 3H₂(g) 2NH₃(g) If the reaction is made to go to completion, what volume of ammonia, NH₃, (in dm³) can be prepared from 25 dm³ of nitrogen and 60 dm³ of hydrogen? All volumes are measured at the same temperature and pressure. A. 40 B. 50 C. 85 D. 120

16 ANSWER Consider the following reaction. N₂(g) + 3H₂(g) 2NH₃(g) If the reaction is made to go to completion, what volume of ammonia, NH₃, (in dm³) can be prepared from 25 dm³ of nitrogen and 60 dm³ of hydrogen? All volumes are measured at the same temperature and pressure. A. 40 B. 50 C. 85 D. 120

17 Bell-Ringer Phosphorus(V) oxide, P₄O₁₀ (Mr = g/mol), reacts vigorously with water (Mr = g/mol), according to the equation below. P₄O₁₀ + 6H₂O 4H₃PO₄ A student added 5.00 g of P₄O₁₀ to 1.50 g of water. Determine the limiting reactant, showing your working. QUIZ IS ON MONDAY (EVEN) & TUESDAY (ODD)

18 ANSWER Phosphorus(V) oxide, P₄O₁₀ (Mr = g/mol), reacts vigorously with water (Mr = g/mol), according to the equation below. P₄O₁₀ + 6H₂O 4H₃PO₄ A student added 5.00 g of P₄O₁₀ to 1.50 g of water. Determine the limiting reactant, showing your working. Water is the limiting reactant

19 PRACTICE Phosphorus(V) oxide, P₄O₁₀ (Mr = g/mol), reacts vigorously with water (Mr = g/mol), according to the equation below. P₄O₁₀ + 6H₂O 4H₃PO₄ A student added 5.00 g of P₄O₁₀ to 1.50 g of water. Determine the limiting reactant, showing your working. Calculate the mass of phosphoric(v) acid, H₃PO₄, formed in the reaction.

20 ANSWER Phosphorus(V) oxide, P₄O₁₀ (Mr = g/mol), reacts vigorously with water (Mr = g/mol), according to the equation below. P₄O₁₀ + 6H₂O 4H₃PO₄ A student added 5.00 g of P₄O₁₀ to 1.50 g of water. Determine the limiting reactant, showing your working. Calculate the mass of phosphoric(v) acid, H₃PO₄, formed in the reaction grams

21 PRACTICE The equation for the complete combustion of butane is 2C₄H₁₀ + 13O₂ 8CO₂ + 10H₂O What is the amount (in mol) of carbon dioxide formed by the complete combustion of three moles of butane? A. 4 B. 8 C. 12 D. 24

22 ANSWER The equation for the complete combustion of butane is 2C₄H₁₀ + 13O₂ 8CO₂ + 10H₂O What is the amount (in mol) of carbon dioxide formed by the complete combustion of three moles of butane? A. 4 B. 8 C. 12 D. 24

23 PRACTICE The equation for a reaction occurring in the synthesis of methanol is CO₂ + 3H₂ CH₃OH + H₂O What is the maximum amount of methanol that can be formed from 2 mol of carbon dioxide and 3 mol of hydrogen? A. 1 mol B. 2 mol C. 3 mol D. 5 mol

24 ANSWER The equation for a reaction occurring in the synthesis of methanol is CO₂ + 3H₂ CH₃OH + H₂O What is the maximum amount of methanol that can be formed from 2 mol of carbon dioxide and 3 mol of hydrogen? A. 1 mol B. 2 mol C. 3 mol D. 5 mol

25 PRACTICE A 500g sample of Al₂(SO₄)₃ is reacted with 450g sample of Ca(OH)₂. A total of 596g of CaSO₄ is produced. What is the limiting reagent in this reaction, and how many moles of excess reagent are unreacted? Al₂(SO₄)₃(aq) + 3Ca(OH)₂(aq) 2Al(OH)₃(s) + 3CaSO₄(s)

26 ANSWER A 500g sample of Al₂(SO₄)₃ is reacted with 450g sample of Ca(OH)₂. A total of 596g of CaSO₄ is produced. What is the limiting reagent in this reaction, and how many moles of excess reagent are unreacted? Al₂(SO₄)₃(aq) + 3Ca(OH)₂(aq) 2Al(OH)₃(s) + 3CaSO₄(s) The limiting reagent is Al₂(SO₄)₃ There are 1.69 mol of Ca(OH)₂ left unreacted.

27 PERCENT YIELD In all of these experiments, we have been calculating what should theoretically be produced (yielded) in a chemical reaction based on how much of the reactants we have. We refer to this as a theoretical yield. If we were to actually perform the experiment and measure how much of the product we experimentally yielded (experimental yield), then we could calculate the percent yield. The percent yield gives us an idea of how close we got to what we theoretically should have been able to produce. Random errors and inaccuracies may occur that lead us to not produce the maximum amount of product that we want. For instance, if you do not use up ALL of the limiting reactant in actuality, then you will not produce the theoretical yield. Percent yield = Experimental yield x 100% Theoretical yield

28 PRACTICE Calcium carbonate decomposes on heating as shown below. CaCO₃ CaO + CO₂ When 50 g of calcium carbonate are decomposed, 7 g of calcium oxide are formed. What is the percentage yield of calcium oxide? A. 7% B. 25% C. 50% D. 75%

29 ANSWER Calcium carbonate decomposes on heating as shown below. CaCO₃ CaO + CO₂ When 50 g of calcium carbonate are decomposed, 7 g of calcium oxide are formed. What is the percentage yield of calcium oxide? A. 7% B. 25% C. 50% D. 75%

30 QUIZ 1. SIT ONLY WHERE YOU SEE A PERIODIC TABLE 2. Take out a sheet of paper, a pen/pencil, and a calculator. 3. THERE IS ONE BATHROOM PASS. DO NOT EXIT THE ROOM WITHOUT THAT PASS. 4. No bathroom/exiting room until quiz is complete. No phones until all quizzes are complete.

31 TODAY 1. Bio Camp is taking place in my room. HOWEVER, there are still QUIZ MAKEUPs 2. All others: AP Studying