Proportional Relationships

Transcription

1 Stoichiometry Video

2 Proportional Relationships 2 1/4 c. flour 1 tsp. baking soda 1 tsp. salt 1 c. butter 3/4 c. sugar 3/4 c. brown sugar 1 tsp vanilla extract 2 eggs 2 c. chocolate chips Makes 5 dozen cookies. I have 5 eggs. How many cookies can I make? 5 eggs 5 doz. 2 eggs Ratio of eggs to cookies = 12.5 dozen cookies

3 STOICHIOMETRY The proportional relationship between two or more substances (reactants & products) during a chemical reaction Allows you to convert from one unit to another for different chemicals in a reaction Mole Ratio: The coefficients in a balanced chemical reaction show the # of moles of each substance Used to convert from moles of one substance to moles of another

4 STEPS TO DO STOICHIOMETRY PROBLEMS 1. Write the chemical reaction 2. Balance the chemical reaction (using coefficients) 3. Assume the coefficient stands for the # of moles of each substance 4. Write out mole-mole ratio in equation

5 Mole Mole Problem How many moles of KClO 3 must decompose in order to produce 9 moles of oxygen gas? 2KClO 3 2KCl + 3O 2? mol 9 mol 9 mol O 2 2 mol KClO 3 3 mol O 2 = 6 mol KClO 3

6 Another example 2KClO 3 2KCl + 3O 2 How many moles of KCl will be produced if you have 3.1 moles of O 2

7 MOLE MASS PROBLEMS How many grams of water can be formed from 2.5 moles of ethyne gas (C 2 H 2 ) reacting with excess oxygen gas? C 2 H 2 + O 2 H 2 O + CO 2

8 MASS MOLE PROBLEM 2 C 2 H O 2 2 H 2 O + 4 CO 2 How many moles of O 2 must react to produce 12.7g of CO 2?

9 MASS MASS PROBLEM If 20.0g of magnesium react with excess hydrochloric acid, how many grams of magnesium chloride are produced? Mg + HCl MgCl 2 + H 2

10 MASS PARTICLES PROBLEM 3.47 x formula units of potassium sulfate will make how many grams of mercury (II) sulfate? K 2 SO 4 + Hg(NO 3 ) 2 KNO 3 + HgSO 4

11 MASS-VOLUME PROBLEM How many liters of oxygen gas, at STP can be collected from the complete decomposition of 50.0 g of potassium chlorate 1. Write a balanced equation g? Liters at STP g/mole 22.4 L/mole Write down 1 the mole given any KClOinformation from the 3 3 mole O necessary to L O 2 change problem Xthe under given measurements the X corresponding X = to moles. (i.e. 1 molar chemical mass compound or g KClO molar 3 2 mole KClO volume at 3 STP.) 1 mole O g KClO 3 2 KClO 3(s) 2 KCl (s) + 3 O 2(g) 6. Stoichiometry Step. This step allows you to L go O 2 from gas Start Using the problem information with under your your given given over and one. one compound to another legally. Only use the 7. convert coefficients Convert grams moles to in front to moles. of the the appropriate compounds involved unit using in the gathered information, Calculate answer. problem

12 MASS TO VOLUME PROBLEM 456L of oxygen gas will react to produce what mass of water? C 6 H 14 + O 2 CO 2 + H 2 O

13 VOLUME VOLUME PROBLEM If you have L of hydrogen gas, how many liters of nitrogen gas do you need to produce ammonia? N 2 + H 2 NH 3

14 PARTICLE PARTICLE PROBLEM Just like volume volume can be made a one step problem, so can a particle particle problem. Mass Mass is still a 3-step problem, because the molar mass of each chemical is always different!!!

15 PARTICLE MOLE PROBLEM If 4.78 x molecules of carbon dioxide is produced, how many moles of C 5 H 12 must react? C 5 H 12 + O 2 CO 2 + H 2 O

16 VOLUME MOLE PROBLEM What volume of H 2 O is produced, if you have 4.2 moles of O 2? C 5 H 12 + O 2 CO 2 + H 2 O

17 Limiting Reactants The reactant that limits the amount of products formed in a chemical reaction Also called the limitor It will be completely used up in the reaction Other reactant(s) will have some amount unchanged or left over - said to be in excess reactant

18 The quantities of the products formed in a reaction are always determined by the quantity of the limiting reactant To determine the limiting reactant: 1. Write balanced chemical reaction 2. Calculate the mass of products formed by each amount of reactant (do 2 mass ---> mass conversion problems) 3. The limiting reactant = the reactant that produces the least amount of product

19 Ex. Identify the limiting reactant when 1.7g of sodium reacts with 2.6L of chlorine gas at STP to produce sodium chloride Na + Cl 2 NaCl

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22 Ex. When 9.00 g of aluminum reacts with excess of phosphoric acid, 30.0 g of aluminum phosphate is produced. What is the % yield of this reaction? 2 H 3 PO Al 2 AlPO H 2

23 A reaction is expected to produce 2.6 L of oxygen gas. In reality, the reaction only produces 0.9 L of oxygen gas. The percent yield of the reaction is