1)  Mass / Mass reactions -
    Problem where the mass of one substance is determined from the mass of another substance in the reaction; solved by using the molar ratio indicated by the balanced chemical equation.
 

Example -
    Powered Aluminum reacts with Iron (III) Oxide to produce Aluminum oxide and molten iron.  What mass of Aluminum Oxide is produced when 2.3g of Aluminum reacts with Iron (III) Oxide?
2.3g
2 Al + Fe2O3 ---> 2 Fe + Al2O3
2(27)                               2(27)+3(16)
54                                    102
            2.3(102 / 54) = 4.34g of Al2O3
 

2)  Volume / Volume  reactions -
    Problem where the volume of one substance is determined from the volume of another substance in the reaction; solved by using the molar ration of the two substances as indicated by the balanced chemical equation.
 

Example -
    If .38 of Hydrogen reacts with Chlorine gas,  what volume of Hydrogen Chloride gas will be produced?

H2 + Cl2 ---> 2 HCl
            .38L H2 (2L HCl / 1L H2) = .76 L HCL.

3)  Mass / Volume reactions -
    Problem where the volume of one substance is determined from the mass of another substance in the reaction; solved by using the molar ratio of the two substances as indicated by the balanced chemical equation.
 

Example -
    If a sample contains  4.0g of NaHCO3, what volume of Carbon Dioxide gas is produced at STP?
4.0g                                                  22.4 (use 22.4 when you use gasses, measured in liters)
2 NaHCO3 ---> Na2CO3 + H2O + CO2
2(23+1+12+16*3)
168
        4.0 (22.4/168) = .53
 

4)  Limiting Reactant problems -
    Reactant that is completely used up in the chemical reaction and that therefore determines the maximum amount of product that can be formed.
 

Example -
    What mass of Lead (II) Iodide will be produced when 16.4g of Lead (II) nitrate is added to 28.5g of Potassium Iodide?  What is the limiting reactant?
16.4g          28.5g
Pb(NO3)2 + 2 KI ---> PbI2 + 2 KNO3
(207+14*2+16*3)   2(39+127)
283                               332

16.4 / 283                 28.5 / 332
   .057                           .858

Since .057 is less than .858 Lead Iodide is the limiting reactant
 

5)  Percent Yield -
    Actual yield divided by the expected yield times 100 percent.
 

Example -
    A piece of Copper with a mass of 5.00g is placed in a solution of silver (I) nitrate containing excess AgNO3.  The Silver metal produced has a mass of 15.2g. What is the percent yield of this reaction?

Cu + 2 AgNO3 ---> 2 Ag + Cu(NO3)2

5.00g Cu * 1 mol Cu / 63.5g Cu * 2 mol Ag / 1 mol Cu * 107.9g Ag / 1 mol Ag = 17.0 = expected yield
15.2 = actual yield       15.2 / 17.0 * 100% = 89.4%.
    The Percent Yield is 89.4%.

1) The coefficients in a balanced chemical equation represent ratios of all of the following except

A) Mass
B) Moles
C) Volumes
D) Particles
 

2) The equation for the synthesis of ammonia is N2+3H2 --> 2NH3.  How many moles of H2 are needed to produce 6 mol NH.

A) 4
B) 6
C) 8
D) 9
 

3) What mass of copper is produced when 3.8 g of iron (Fe) reacts with excess copper (II) sulfate according to the equation Fe + CuSO4 --> FeSO4 + Cu?

A) 6.4g
B) 4.3g
C) 3.3g
D) 3.8g
 

4) If 16.4g Na2CrO4 are combined with 26.2g AgNO3 in a double-replacement reaction, what will be the limiting reactant?

A) Na2CrO4
B) AgNO3
C) NaNO3
D) Ag2CrO4
 

5) Magnesium reacts with hydrochloric acid according to the following equation: Mg+2HCl --> MgCl2+H2.  If .30 mole of Mg reacts, how many molecules of HCl will also react?

A) 2.0 e24
B) 1.8 e23
C) 3.0 e23
D) 3.6 e23
 

6) If 3.0L CH4 are burned according to the equation: CH4 + 2O2 ? CO2 + 2H2O, what volume of Carbon Dioxide will be produced STP?

A) 3.0L
B) 44L
C) 132L
D) 6.0L
 

7) Percent Yield is the quantity of product actually produced compared with the quanity

A) of product expected
B) of the limiting reactant
C) usually produced on average
D) of the reactant in excess
 

Fill in the Blank

8) The total _______________________ of reactants is always equal to that of the products.

9) All stoichiometry problems are based upon the _____________ molar ratios that exist between the substances in the reaction.

10) When 3 moles of calcium chlorate are decomposed in the reaction Ca (CLO3)2  CaCl2 + 3O2, ___    moles of oxygen gas are produced.

11) The ________________ determines the quantity of products in a chemical reaction.

12) When 5.0g of Aluminum combine with 3.0g of Sulfur to produce aluminum sulfide (Al2S3), the limiting reactant is __________.

13) The amount of product recovered from the chemical reaction is the ___________ yield.

1.) Describe stoichiometry and its role in chemistry.

Stoichiometry is the study of the quantitative, or measurable, relationships that exist in chemical formulas and chemical reactions. A great deal of valuable chemistry relies on Stoichiometry calculations.

2.) Explain why a balanced chemical equation is necessary to solve a stoichiometry problem.

Without a correctly balanced equation any calculation based on the amount of material involved will be incorrect.

3.) Explain why it is necessary to convert given units of a substance to moles when solving a stoichiometry problem.

Moles are needed to be able to interpret a balanced equation.

4.) 3.27 grams of Zinc (Zn) react with excess hydrochloric acid (HCL) to produce Zinc Chloride and Hydrogen gas. Find the grams of each product formed. (use 35.5g for Cl)

Zinc Chloride 6.8g

5.) 98 grams of potassium chlorate (KCLO3) decomposes into potassium chloride (KCl) and oxygen gas (O). Calculate the volume in liters of oxygen formed. How many grams of potassium chloride are formed?

Oxygen 26.8 liters

6.) Hydrogen and Oxygen react to produce hydrogen peroxide.  If 80 grams of hydrogen peroxide are formed, then how many grams of OXYGEN are needed?

75.3g of Oxygen

7.) In a reaction between sulfur and oxygen, 45g of sulfur dioxide are formed.  How many grams of sulfur are needed?

22.5g sulfur

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