stoichiometry 2nd tri 0910

Shhhh…Shhhh…Don’t say the “S” word!Don’t say the “S” word!

(But what is the “S” word in Chemistry?)

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StoichiometryStoichiometry!!Stoichi-what??!!Stoichi-what??!!

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StoichiometryStoichiometry!!

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To Review...To Review...

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• Method:

• Practice:

Find the mass on the PT for each element, multiply by subscripts; add them together.

What is the molar mass of Ba(C2H3O2)2?

255.3 g/mol

•Calculating Molar Mass (section title)

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[What is the molar mass of [What is the molar mass of Ca(OH)Ca(OH)22?]?]

A. [57.1 g/mol]

B. [74.1 g/mol]

C. [114.2 g/mol]

D. [none of these]

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Changing Grams to MolesChanging Grams to Moles

• Method:

• Practice:

1) Use molar mass and dimensional analysis to convert

How many moles are contained in 23.995 g of barium acetate? (see notes above)

0.09399 mol

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In order to change grams to moles, In order to change grams to moles, you must divide the molar mass by you must divide the molar mass by the mass. the mass. A. True

B. False

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[Convert 15.0 g of CO[Convert 15.0 g of CO22 to moles. ] to moles. ]

A. 0.341 mol

B. 59 mol

C. 660. mol

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Changing moles to gramsChanging moles to grams

• Method:

• Practice:

1. Use molar mass and dimensional analysis to convert

How many grams are in .000115 moles of barium acetate?

0.0294 g

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You convert moles to grams by You convert moles to grams by multiplying moles by molar mass.multiplying moles by molar mass.A. True

B. False

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What is the mass of 3.4 moles of What is the mass of 3.4 moles of aluminum hydroxide, Al(OH)aluminum hydroxide, Al(OH)33? ?

A. 156.4 g

B. 207.4 g

C. 265.2 g

D. 294.1 g

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Balancing equationsBalancing equations

• Method:

• Practice:

1. Count atoms of each element on each side of the equation.

2. Add coefficients (big numbers in front) to make each kind of atom the same on both sides.

C5H12 + O2 --> CO2 + H2O

C5H12 + 8O2 --> 5CO2 + 6H2O

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more balancing practice...more balancing practice...

• PbO2 PbO + O2

• AlCl3 + Na2CO3 NaCl + Al2(CO3)3

•2PbO2 2PbO + O2

• 2AlCl3 + 3Na2CO3 6NaCl + Al2(CO3)3

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A. 1

B. 2

C. 3

D. 4

Given the unbalanced equation:

Mg(ClO3)2 → MgCl2 + O2 What is the coefficient of O2 when the equation is balanced correctly using the smallest whole number coefficients?

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Stoichiometry is...Stoichiometry is...

• the calculation of quantities in chemical equations

•important because it allows chemists to determine how much of a reactant is needed or how much product can be made

•based on balanced chemical equations

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General Steps General Steps (section title)(section title)

1. Convert given amount to moles.

2. Put calculated moles over 'X' and set it equal to the ratio.

3. Set up a ratio of the coefficients of the given over the unknown.

4. Solve for 'X' (cross-multiply & divide)

5. Convert moles to the unit requested.

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Mole RatiosMole Ratios

• Used to determine the proportions that chemicals react with each other

• Determined by looking at the coefficients in the balanced equation

• Ex. 2H2 + O2 2H2O

– Ratio of H2 to O2 is 2:1

– Ratio of H2O to H2 is 2:2

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A. 1:1

B. 1:2

C. 3:1

D. 3:2

In the reaction, N2 + 3 H2 --> 2 NH3, what is the mole ratio of hydrogen to nitrogen?

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Mole-Mole problems Mole-Mole problems (section title)(section title)

• Recognizing: Given is in moles; unknown is in moles

• Practice: C3H8 + O2 CO2 + H2O How many moles of CO2 can be produced by .675 moles of C3H8?

2.03 mol CO2

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Given the reaction CHGiven the reaction CH44 + 20 + 2022 --> C0 --> C022 + +

2H2H220, What amount of oxygen is needed 0, What amount of oxygen is needed

to completely react with 1 mole of CHto completely react with 1 mole of CH44??

A. 2 moles

B. 2 atoms

C. 2 grams

D. 2 molecules

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Given the reaction:

C6H12O6 + 6O2 → 6CO2 + 6H2O

How many moles of C6H12O6 are needed to produce 24 moles of carbon dioxide?

A. 1.0 mol

B. 12 moles

C. 24 moles

D. 4.0 moles

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Mass-Mass problems Mass-Mass problems (section title)(section title)

• Recognizing: given is in grams, unknown is in grams

• Practice – C3H8 + O2 CO2 + H2O What mass of propane is needed to produce 44.5 grams of water?

27.2 g C3H8

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Any time you calculate an amount of product from

a balanced equation, this is called

“Theoretical Yield”

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Volume-Volume problems: Volume-Volume problems: (section title) (section title)

• 1 mole of any gas at STP (standard temperature and pressure) = 22.4 L

• Recognizing – both given and unknown are in liters or mL

• Practice – C3H8 + O2 CO2 + H2O What volume of oxygen gas is needed to produce 50.0 L of water vapor?

62.5 L O2

*** Refers to volume of gases

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How do I get to Walmart??How do I get to Walmart??

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Mass & Volume Problems Mass & Volume Problems (section title)(section title)

• Recognizing: given is either in grams or liters; unknown is also in either one

• Practice:

C3H8 + O2 CO2 + H2O

What volume of CO2 gas can be produced when 150.0 g of propane are burned?

229.1 L CO2

Any time you calculate an amount of product from

a balanced equation, this is called

“Theoretical Yield”

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Limiting ReactantLimiting Reactant

• The chemical in a reaction that will be used up first is the limiting reactant; controls how much product can be made

• The reactant in excess is the one(s) not used up first

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A. A is the limiting reactant

B. B is the limiting reactant

C. There is no limiting reactant

D. Both A and B are limiting reactants

In the reaction A + B --> C + D, if element B is in excess, then -

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To determine limiting reactant…To determine limiting reactant…

• For each reactant, do a stoic problem to determine how many moles of a product can be made. (If there is more than one product, just pick one.)

• Which ever reactant leads to the least amount of product is the limiting reactant.

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Limiting Reactant Practice:Limiting Reactant Practice:

Practice: C3H8 + O2 CO2 + H2O

• If you begin with 45.0 g of propane and 65.0 g of oxygen, what is the limiting reactant?

O2 is the limiting reactant

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In the given equation, which substance In the given equation, which substance is limiting, if 3.7 moles of potassium, K is limiting, if 3.7 moles of potassium, K are reacted with 3.7 moles of nickel are reacted with 3.7 moles of nickel sulfate, Nisulfate, Ni22SOSO44??

A. K

B. K2SO4

C. Ni

D. NiSO4

2K + NiSO4 K2SO4 + Ni

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More Stoic stuff…More Stoic stuff…

• Actual yield is how much product was made.

• Theoretical yield is how much product should have been made. (we already talked about this!)

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Percent Yield Percent Yield (section title)(section title)

• Percent yield is a calculation to determine the efficiency of a chemical process.

• Formula: • % yield = (actual yield/theoretical yield) x 100 % yield = (actual yield/theoretical yield) x 100

• Practice: During an experiment, a student produced 63.0 g of copper. According to his calculations, he should have made 68.0 g. What was his percent yield?

92.6 % yield