final information open-ended: 6/11 (review 6/10) last day to ask questions for mc 6/14 topics:...

Final Information

• Open-ended: 6/11 (review 6/10)• Last day to ask questions for MC 6/14• Topics:

– Bonding– Reactions

• Chemical Equations (balancing, types)– Percent Composition– Molar Mass, Avogadro’s Number, conversions– Empirical Formula– Stoichiometry

• Limiting reactants• Mole-mole, grams-grams, particles-particles conversions

Stoichiometry

FlowchartFlowchartAtoms or Molecules

Moles

Mass (grams)

Divide by 6.02 X 1023

Multiply by 6.02 X 1023

Multiply by atomic/molar mass from periodic table

Divide by atomic/molar mass from periodic table

molar mass Avogadro’s numbermolar mass Avogadro’s number Grams Grams MolesMoles particles particles

Everything must go through Everything must go through Moles!!!Moles!!!

CalculationsCalculations

Chemistry RecipesChemistry Recipes

Looking at a reaction tells us how much of Looking at a reaction tells us how much of something you need to react with something you need to react with something else to get a product (like the something else to get a product (like the cookie recipe)cookie recipe)

Be sure you have a balanced reaction Be sure you have a balanced reaction before you start!before you start!

Example: 2 Na + ClExample: 2 Na + Cl2 2 2 NaCl 2 NaClThis reaction tells us that by mixing 2 moles of This reaction tells us that by mixing 2 moles of

sodium with 1 mole of chlorine we will get 2 moles sodium with 1 mole of chlorine we will get 2 moles of sodium chlorideof sodium chloride

What if we wanted 4 moles of NaCl? 10 moles? What if we wanted 4 moles of NaCl? 10 moles? 50 moles?50 moles?

Example Example QuestionsQuestions

Write the balanced reaction for hydrogen gas Write the balanced reaction for hydrogen gas reacting with oxygen gas.reacting with oxygen gas.

2 H2 H22 + O + O22 2 H 2 H22OO How many moles of reactants are needed?How many moles of reactants are needed? What if we wanted 4 moles of water?What if we wanted 4 moles of water? What if we had 3 moles of oxygen, how much hydrogen What if we had 3 moles of oxygen, how much hydrogen

would we need to react, and how much water would we would we need to react, and how much water would we get?get?

What if we had 50 moles of hydrogen, how much oxygen What if we had 50 moles of hydrogen, how much oxygen would we need, and how much water produced? would we need, and how much water produced?

Consider : 4NH3 + 5O2 6H2O + 4NO• How many moles of H2O are produced if

0.176 mol of O2 are used?

• How many moles of NO are produced in the reaction if 17 mol of H2O are also produced?

6 mol H2O 5 mol O2

x

Stoichiometry questions (1)

# mol H2O= 0.176 mol O2 0.2112 mol H2O

=

4 mol NO 6 mol H2O

x # mol NO= 17 mol H2O11.33 mol NO

=

Notice that a correctly balanced equation is essential to get the right answer

Consider : 4NH3 + 5O2 6H2O + 4NO• How many grams of H2O are produced if 1.9

mol of NH3 are combined with excess oxygen?

• How many grams of O2 are required to produce 0.3 mol of H2O?

6 mol H2O 4 mol NH3

x


# g H2O=1.9 mol NH3

51.4 g H2O

= 18.02 g H2O 1 mol H2O

x

5 mol O2 6 mol H2O

x

# g O2=0.3 mol H2O

8 g O2= 32 g O2 1 mol O2

x

Mass-Mass ConversionsMass-Mass Conversions

Most often we are given a starting mass Most often we are given a starting mass and want to find out the mass of a product and want to find out the mass of a product we will get (called theoretical yield) or how we will get (called theoretical yield) or how much of another reactant we need to much of another reactant we need to completely react with it (no leftover completely react with it (no leftover ingredients!)ingredients!)

Now we must go from grams to moles, Now we must go from grams to moles, mole ratio, and back to grams of mole ratio, and back to grams of compound we are interested incompound we are interested in

Mass-Mass ConversionMass-Mass Conversion

Ex. Calculate how many grams of Ex. Calculate how many grams of ammonia are produced when you react ammonia are produced when you react 2.00g of nitrogen with excess hydrogen.2.00g of nitrogen with excess hydrogen.

NN2 2 + 3 H+ 3 H2 2 2 NH 2 NH33

2.00g N2 1 mol N2 2 mol NH3 17.06g NH3

28.02g N2 1 mol N2 1 mol NH3

= 2.4 g NH3

Consider : 4NH3 + 5O2 6H2O + 4NO• How many grams of NO is produced if 12 g of

O2 is combined with excess ammonia?

4 mol NO 5 mol O2

x


# g NO=

12 g O2

9.0 g NO=

30.01 g NO 1 mol NO

x 1 mol O2 32 g O2

x

• Notice that we cannot directly convert from grams of one compound to grams of another. Instead we have to go through moles.

• Many stoichiometry problems follow a pattern: grams(x) moles(x) moles(y) grams(y)

• We can start anywhere along this path depending on the question we want to answer

Q- for the reaction 2H2 + O2 2H2O what is the path we would take for the following

• Given 2 moles H2O, calculate grams H2O?• Moles O2 required for 36 g H2?• Grams of H2O produced from 6 grams O2?
















Converting grams to grams

Moving along the stoichiometry path• We always use the same type of information

to make the jumps between steps:

grams (x) moles (x) moles (y) grams (y)

Molar mass of x Molar mass of y

Mole ratio from balanced equation

Given: 4NH3 + 5O2 6H2O + 4NOa) How many moles of H2O can be made using 0.5 mol NH3? b) what mass of NH3 is needed to make 1.5 mol NO? c) how many grams of NO can be made from 120 g of NH3?

4NH3 + 5O2 6H2O + 4NOa)

b)

c)

Answers

6 mol H2O 4 mol NH3

x # mol H2O= 0.5 mol NH3 0.75

mol H2O=

4 mol NH3

4 mol NOx

# g NH3=1.5 mol NO 25.6 g

NH3

= 17.04 g NH3

1 mol NH3

x

4 mol NO 4 mol NH3

x

# g NO=

120 g NH3

211 g NO=

30.01 g NO 1 mol NO

x 1 mol NH3 17.04 g NH3

x

More Stoichiometry QuestionsFollow the rules for significant digits. Show all calculations.

1. 2 C4H10 + 13 O2 -> 8 CO2 + 10 H2O

a) what mass of O2 will react with 400 g C4H10?

b) how many moles of water are formed in a)?2. 3 HCl + Al(OH)3 -> 3 H2O + AlCl3

How many grams of aluminum hydroxide will react with 5.3 moles of HCl?

3. Ca(ClO3)2 -> CaCl2 + 3 O2

What mass of O2 results from the decomposition of 1.00 kg of calcium chlorate?

4. The reaction of Ca with water can be predicted using the activity series. What mass of water is needed to completely react with 2.35 g of Ca?

5. Fe2O3 + 3CO -> 2Fe + 3CO2.

a) How many moles of carbon monoxide are required to react with 163.0 g of iron(III) oxide?

b) How many grams of CO2 are produced from a reaction that also produces 23.9 grams of Fe?

6. 3Cu + 8HNO3 3Cu(NO3)2 + 4H2O + 2NO

a) how many moles of copper(II) nitrate can be prepared from 17.0 moles of Cu?

b) how many grams of copper(II) nitrate can be prepared using 3.8 moles of HNO3?

c) what mass of water results from the reaction of 8.50 kg of copper metal?

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final information open-ended: 6/11 (review 6/10) last day to ask questions for mc 6/14 topics:...

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