Chapter 12 - Chapter 12 - StoichiometryStoichiometry

I ‘m back!I ‘m back!

Objective: To learn how to use a complete chemical equation to calculate quantities of

a substance

Chemical Equations

Remember that a balanced chemical equation provides the same kind of quantitative information that a recipe does.

From the specific amounts of the ingredients, a specific amount of cookies can be made. Due to this, proportional relationships proportional relationships b/w the ingredients and the products can be written.

What would happen if you add more or less of 1 ingredient?

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.

1)1) 1 tsp. baking soda = 2 c. chocolate chips1 tsp. baking soda = 2 c. chocolate chips2)2) 1 c butter= 2 eggs1 c butter= 2 eggs3)3) 5 dz cookies = 1tsp. Salt5 dz cookies = 1tsp. Salt4)4) 5 dz cookies = ¾ c. sugar5 dz cookies = ¾ c. sugarETC.ETC.

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= 12.5 dozen cookies

Ratio of eggs to cookies

StoichiometryStoichiometry StoichiometryStoichiometry - - The study of quantities of materialsThe study of quantities of materials consumedconsumed & &

producedproduced in chemical reactions.in chemical reactions.• Uses a balanced chemical equationUses a balanced chemical equation• Similar to bookkeeping.Similar to bookkeeping.• Based on Based on MOLE RATIOSMOLE RATIOS

Interpreting Balanced Equations Interpreting Balanced Equations 2H2 + O2 2H2O

2 molecules of hydrogen and 1 molecule 2 molecules of hydrogen and 1 molecule of oxygen form 2 molecules of water.of oxygen form 2 molecules of water.

2 moles of hydrogen and 1 mole of 2 moles of hydrogen and 1 mole of oxygen form 2 moles of water.oxygen form 2 moles of water.

2 dozen molecules hydrogen and 1 2 dozen molecules hydrogen and 1 dozen molecules of oxygen form 2 dozen dozen molecules of oxygen form 2 dozen molecules of water.molecules of water.

2 moles Mg2 moles Mg

1 mole O1 mole O22

2 moles MgO2 moles MgO

2 mole Mg2 mole Mg

2 moles MgO2 moles MgO

1 mole O1 mole O22

1 mole O1 mole O222 moles MgO2 moles MgO

2 mole Mg2 mole Mg

2 moles MgO2 moles MgO

1 mole O1 mole O22

2 moles Mg2 moles Mgor

or

or

Mole Ratio Mole Ratio tells the ratio between 2 substances in a balanced chemical equation.

• indicated by coefficients in a balanced equationindicated by coefficients in a balanced equation

• Ex. 22 Mg + OMg + O22 2 MgO 2 MgO

LAW of CONSERVATION of MASSLAW of CONSERVATION of MASSThe MOLE relationships can also apply to mass relationships. We can check this converting from grams to moles.

1 mole O232.00 g O2

1 mole O2

= 32.00 g O2

36.04 g H36.04 g H2 2 + O+ O22

2H2 + O2 2H2O

2 moles H2O

Product:Product:

4.04 g H22 moles H2

2.02 g H2

1 mole H2

=

Reactants:Reactants:

18.02 g H2O1 mole H2O

= 36.04 g H36.04 g H22OO

Steps to Calculate Stoichiometric Problems

1. Correctly balance the equation.

2. Convert the given amount into moles.

3. Set up mole ratios.

4. Use mole ratios to calculate moles of desired chemical.

5. Convert moles back into final unit.

Types of CalculationsTypes of Calculations

1. 1. mole to molemole to mole

Remember the Remember the mole ratiomole ratio is the ratio is the ratio between between any two substances any two substances in a reaction in a reaction and and will be used in all calculationswill be used in all calculations

Ex. 1 How many How many moles of Omoles of O22 are produced when are produced when

3.34 moles of Al3.34 moles of Al22OO33 decompose? decompose?

2 Al2 Al22OO33 AlAl ++ 3O3O22

3.34 mol Al2O33 mol O2 mol Al2O3

= 5.01 mol O5.01 mol O222

**Practice problem 1:Practice problem 1: C2H2 + O2 CO2 + H2O (unbalanced)

If 3.84 moles of C2H2 are burned, how many moles of O2 are needed?

2. 2. moles to gramsmoles to grams given moles given moles mole ratio mole ratio molar mass molar mass

types of problems (continued)types of problems (continued)

Ex. 2 If 1.50 moles of Fe are used , how many grams of copper II sulfate would form?

2Fe + 3CuSO4 Fe2(SO4)3 + 3Cu

1.50 mol of Fe 3 mol CuSO4

2 mol Fe 1 mol CuSO4

159.62 g 159.62 g CuSO4

== 359 g359 g CuSO4

**Practice problem 2Practice problem 2: : CC22HH22 + O + O22 CO CO22 + H + H22O O

If 0.750 moles of O2 are used, how many grams of C2H2 are burned?

3. g3. grams to molesrams to moles

given mass given mass molar mass molar mass mole ratio mole ratio

Ex. 3 If Ex. 3 If 146 g of NaCl146 g of NaCl are produced in the following are produced in the following reaction, how many reaction, how many moles of Clmoles of Cl2 2 were consumed? were consumed? 2Na + Cl2Na + Cl22 2NaCl 2NaCl

146 g NaCl 1 mol NaCl 1 mol Cl146 g NaCl 1 mol NaCl 1 mol Cl22 = 1.25 mol = 1.25 mol

58.44 g NaCl58.44 g NaCl 2 mol NaCl

types of problems (continued)types of problems (continued)4. g4. grams to gramsrams to grams

given mass given mass molar mass molar mass mole ratio mole ratio molar mass molar mass

Ex. 4 Ex. 4 If 10.8 g of Fe are added to a solution of CuSO4, how many grams of solid copper would form? 2Fe + 3CuSO4 Fe2(SO4)3 + 3Cu

10.8 g Fe 1 mol Fe 3 mol Cu 63.55 g Cu = 18.4g

55.85 g Fe 2 mol Fe 1 mol Cu

*Practice problem 3: *Practice problem 3: Calculate the no. of moles of CH4 used to produce 1.8 g of H2O.

CH4 + 2O2 CO2 + 2H2O

*Practice problem 4:*Practice problem 4: Zinc reacts with iodine to form zinc iodide (ZnI2). Write the balanced equation for this reaction.Calculate the grams of ZnI2 that would beproduced from a 125.0 g sample of Zn.