Stoichiometry The study of the relative quantities ... · Chap 4 notes.notebook NEW.notebook 1...
Transcript of Stoichiometry The study of the relative quantities ... · Chap 4 notes.notebook NEW.notebook 1...
Chap 4 notes.notebook NEW.notebook
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April 27, 2015
Nov 128:40 AM
Chapter 4: Quantities in Chemical Reactions
4.1 Introducing Stoichiometry
4.2 The Limiting Reactant
4.3 Percentage Yield
Nov 128:41 AM
Stoichiometry
The study of the relative quantities of reactants and products in a chemical reaction.
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April 27, 2015
Nov 128:44 AM
4.1 Introducing Stoichiometry
* How many sandwiches can you make if you have nine slices of bread, six slices of turkey, and twelve strips of bacon?
LAW OF CONSERVATION OF MASS = in any chemical reactions the mass of the reactants is equal to the mass of the products
***We can interpret a chemical equation 4 ways: particles, moles, mass, and volume (if gases).
Apr 209:54 AM
We can interpret a chemical equation 4 ways: particles, mass, moles, and volume (if gases).
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April 27, 2015
Nov 121:20 PM
N2(g) + 3H2(g) 2NH3(g)
Sum it up...
Particles: 1mcul N2 + 3mcul H2 > 2 mcul NH3
Moles: 1mol N2 + 3mol H2 > 2 mol NH3
Mass: 28.0g N2 + 6.1g H2 > 34.1g NH3
34.1 g reactants > 34.1g products
Nov 128:47 AM
Particle Relationships in Balanced Chemical Equations
Ammonia:
This equation tells you that one molecule of nitrogen gas reacts with three molecules of hydrogen gas to form two molecules of ammonia gas.
N2(g) + 3H2(g) 2NH3(g)
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April 27, 2015
Apr 209:55 AM
Mass:
The total mass of elements on the left hand side must equal the total mass of elements on the right hand side.
1C3H8 + 5O2 > 3CO2 + 4H2O
g
Apr 209:59 AM
Mole:
The ratio of the coefficients determines the number of moles.
1C3H8 + 5O2 > 3CO2 + 4H2O
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April 27, 2015
Apr 2010:00 AM
Volume:
Multiply the coefficient by 22.4L
1C3H8 + 5O2 > 3CO2 + 4H2O
Apr 2010:01 AM
MoleMole Calculations:
1. Put a question mark over the one you are trying to find.
2. Put the number of moles over the compound given.
3. Multiply the number given by the coefficient of what you are looking for over the coefficient of what you have.
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April 27, 2015
Nov 121:16 PM
Example 1:
Al(s) + Br2(l) AlBr3(s)
How many moles of Br2 are needed to produce 5 mol of AlBr3 if sufficient Al is present?
*Practice page 115 #5,6
Apr 2010:04 AM
Example 2:
If 3.14 moles of NH3 react with sufficient oxygen, how many moles of H2O are formed?
4NH3 + 5O2 > 4NO + 6H2O
Example 3:
If 0.89 moles of O2 react with sufficient ammonia, how many moles of NO are formed?
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April 27, 2015
Nov 122:46 PM
Mass Relationships in Balanced Chemical Reactions
Equation:
What if we have 10g of N2? How many grams of NH3 would be produced?
• Would it be 20g of NH3 according to the ratio?
• NOOOOOOOOOO!!!
• The equation gives only a MOLE ratio.
N2(g) + 3H2(g) 2NH3(g)
Nov 122:52 PM
Stoichiometric Calculations
• A balanced chemical equation tells you number of moles of reactants and products.
• From moles what can you find? (Hint: think about the mole map)
moles to particles, how?
moles to grams, how?
moles to litres, how?
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April 27, 2015
Nov 132:13 PM
Process for Solving Stoichiometric Calculations
Step 1: Write a balanced chemical equation.
Step 2: If you are given mass, volume, or number of particles of a substance, convert to moles.
Step 3: Use the mole ratio to find number of moles of required (needed) substance based on the moles of given substance.
Step 4: Convert moles of required substance to mass, volume, or number of particles.
Nov 132:20 PM
Mole Bridge
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April 27, 2015
Nov 132:23 PM
Example 1:
Fe(s) + 2HCl(aq) FeCl2(aq) + H2(g)
1. What volume of H2 will be produced if 5.33g of Fe is reacted?
2. How many molecules of FeCl2 will be produced if 13.5L of H2 is made?
3. How many atoms of H are produced from 5.0g of Fe?
Nov 132:28 PM
Example 2:
N2(g) + 3H2(g) 2NH3(g)
1. How many moles of hydrogen gas are required to produce 31.0L of ammonia gas?
2. What mass of nitrogen is required to react with 1.44L of hydrogen?
3. What mass of hydrogen will react with 10.78g of nitrogen gas?
Practice page 121 #11,12,13
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April 27, 2015
Nov 132:48 PM
Review It
C4H10(g) + O2(g) CO2(g) + H2O(l)
1. After balancing the equation above, calculate the volume of carbon dioxide that could be produced if 58.6g of oxygen gas reacted with sufficient butane, C4H10.
2. Calculate the number of water molecules that could be produced if 4.8mols of butane reacted with sufficient oxygen.
Nov 1911:03 AM
3 slices of bread + 4 pieces of turkey + 6 pieces of bacon = one sandwich
Which ingredient limits how many sandwiches you can make?
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April 27, 2015
Nov 1911:07 AM
4.2 The Limiting Reactant
2A + B A2B
Limiting reactant:Excess reactant:
Reactants are said to be in STOICHIOMETRIC AMOUNTS when they are present in the exact amounts predicted by the chemical equation. This means when the reaction goes to completion there are no reactants left.
In real life, there are often reactants left. The reactant that there is too much of is called the EXCESS REAGENT. The reactant that runs out (or is used up) is called the LIMITING REAGENT and it will determine how much product is made.
Nov 1911:09 AM
Thought Lab page 129
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April 27, 2015
Nov 1911:11 AM
Limiting Reactants
Example 1:Li3N(s) + 3H2O(l) NH3(g) + 3LiOH(aq)
If 4.87g of lithium nitride reacts with 5.80g of water, determine the limiting reactant.
Nov 1911:14 AM
Example 2:CH4 + 2O2 CO2 + 2H2O
Determine the limiting reactant if 30.0g of methane (CH4) reacts with 40.0L of oxygen gas.
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April 27, 2015
Nov 1911:17 AM
Example 3:2N2 + O2 2N2O
What volume of N2O should be formed when 30.0g of N2 reacts with 34.5g of O2?
Nov 1911:20 AM
Example 4:Determine the mass of calcium oxide that could be formed with the following:
2Ca + O2 2CaO6.90x1023 27.5Lmolecules
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April 27, 2015
Nov 1911:23 AM
Practice Problems
page 131, 134 #2327
Apr 152:22 PM
Correctpage 134 # 27
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April 27, 2015
Nov 201:47 PM
Review
2Ca + O2 2CaO
a) Determine the limiting reactant if 30.0L of O2 reacts with 122g of Ca.
b) How much of the excess reactant would be left over?
Apr 279:59 AM
Review on MassMass
2N2 + O2 > 2N2O
If you have 64.0g of N2 how many grams of N2O are produced?
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April 27, 2015
Apr 2710:01 AM
Review on Limiting Reagent
Ca(OH)2 + 2HCl > CaCl2 + 2H2O
If you have spilled 6.3 mol of 2HCl and put 2.8 mol of Ca(OH)2 on it:
A. What is the LR?
B. What is the ER?
C. How much excess is left over?
D. How much product is made?
Apr 2710:04 AM
C3H8 + 5O2 > 3CO2 + 4H2O (double trick)
If 2.89 grams of propane reacts with 5.41 grams of oxygen:
A. What is the LR?
B. What is the ER?
C. How much excess is left over?
D. How much product is made?
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April 27, 2015
Nov 279:55 AM
If you have 3+ Reactants
3Na + P + 2O2 Na3PO4
Determine the limiting reactant if 30.5g of sodium reacts with 14.9g of phosphorous and 10.0L of oxygen.
Nov 252:15 PM
THEORETICAL YIELD ‐ the amount of product predicted from a reaction (calculated).
ACTUAL YIELD ‐ the amount of product obtained in an experiment. (in the lab and measured)
Actual yield is usually less than the theoretical because:1. imperfect collection and measuring techniques2. competing side reactions3. impure reactants4. incomplete reactions
PERCENTAGE YIELD ‐ predicts the success of a reaction by comparing the actual yield with the theoretical yield.
Percent Yield = actual x 100% theoretical
4.3 Percent Yield
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April 27, 2015
Apr 2710:07 AM
Hint: Percent yields are just like doing a massmass followed by using the percent yield formula.
Nov 252:22 PM
Calculating Percent Yield
Percentage yield = actual yield x 100theoretical yield
Example: Ammonia can be prepared by reacting nitrogen gas with hydrogen gas.
N2(g) + 3H2(g) 2NH3(g)
If 7.5g of nitrogen gas reacts with sufficient hydrogen gas and the actual yield of ammonia is 1.72g obtained by experiment:
a) What is the theoretical yield of ammonia?
b) What is the percentage yield of the reaction?
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April 27, 2015
Apr 2710:07 AM
Trick used by teachers:
Sometimes teachers combine a limiting reagent and a percent yield. To do this you must use the one you run out of to determine the mass of the product for the theoretical yield!
Nov 38:31 PM
Note: Due to the law of conservation of mass your percent yield should never be higher than 100% (so it is always the smaller yield over the larger yield times 100).