Stoichiometry

Lancaster High School

StoichiometryStoichiometry

Consider the chemical equation:4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

There are several numbers involved. What do they all mean?

““stochio” = ___________stochio” = ___________““metry” = ____________metry” = ____________

  Stoichiometry is about measuring the amounts of Stoichiometry is about measuring the amounts of elements and compounds involved in a reaction. elements and compounds involved in a reaction.

StoichiometryStoichiometry

Recall that Chemical formulas represent numbers of atoms

4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

NH3 __ nitrogen and __ hydrogen atoms

O2 __ oxygen atoms

H2O__ hydrogen atoms and __ oxygen

atom

NO __ nitrogen atom and __ oxygen atom

StoichiometryStoichiometry

Recall that Chemical formulas have molar masses:

4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

NH3 __ g/mol

O2 __ g/mol

H2O __ g/mol

NO __ g/mol

StoichiometryStoichiometry

Recall that Chemical formulas are balanced with coefficients

4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

4 X NH3 = __ nitrogen + __ hydrogen

5 X O2 = __ oxygen

6 X H2O = __ hydrogen + __ oxygen

4 X NO = __ nitrogen + __ oxygen

StoichiometryStoichiometry

With Stoichiometry we find out that 4 : 5 : 6 : 4

do more than just multiply atoms.

4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

4 : 5 : 6 : 4Are what we call a ____ ratio.

StoichiometryStoichiometry4NH4NH33 + 5O + 5O22 6H 6H22O + 4NOO + 4NO

4 : 5 : 6 : 4Can mean either:

4 _________ of NH3 react with 5 _________ of O2

to produce 6 __________ of H2O and 4 _________ of NO

OR

4 ______ of NH3 react with 5 ______ of O2

to produce 6 ______ of H2O and 4 ______ of NO

4NH3 + 5O2 6H2O + 4NO

How many moles of H2O are produced if 2.00 moles of O2 are used?

Stoichiometry Question (1)

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

4 NH3 + 5 O2 6 H2O + 4 NO

How many moles of NO are produced in the reaction if 15 mol of H2O are also produced?

Stoichiometry Question (2)

4 NH3 + 5 O2 6 H2O + 4 NO

How many grams of H2O are produced if 2.2 mol of NH3 are combined with excess oxygen?

Stoichiometry Question (3)

4 NH3 + 5 O2 6 H2O + 4 NO

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

Stoichiometry Question (4)

4 NH3 + 5 O2 6 H2O + 4 NO

How many grams of NO is produced if 12 g of O2 is combined with excess ammonia?

Stoichiometry Question (5)

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)

_______of x _________of y

_____ ratio from ________________

Many stoichiometry problems follow a pattern:

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

Converting grams to grams

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

Notice that we cannot directly convert from grams of one compound to grams of another. Instead we have to go through moles and mole ratio in the balanced equation.

Have we learned it yet?Try these on your own - 4 NH3 + 5 O2 6 H2O + 4 NO

a) How many moles of H2O can be made using 1.6 mol NH3?

b) what mass of NH3 is needed to make 0.75 mol NO?

c) how many grams of NO can be made from 47 g of NH3?