1. and cooking with chemicals
Stoichiometry
and cooking with chemicals

2. Molar Ratio Exothermic Endothermic
OUTCOME QUESTION(S):
C STOICHIOMETRY
Solve stoichiometric problems involving moles, mass, and volume, given the reactants and products in a balanced chemical reaction.
Include: heat of reaction
Identify the limiting reactant and calculate the mass of a product, given the reaction equation and reactant data.
Include: theoretical yield, experimental yield
Vocabulary & Concepts 
Molar Ratio Exothermic Endothermic

3. “The calculation of quantities in chemical reactions”
STOICHIOMETRY
“The calculation of quantities in chemical reactions”
N2 (g) H2 (g)
2 NH3 (g) H N
atomic
1 molecule molecules molecules
molecular
There are many ways to interpret the relationships in a balanced equation…

4. N2 (g) + 3 H2 (g) 2 NH3 (g) 28g + 6g 34g + 1 mole + 3 moles 2 moles
molar
28g g g
mass
22.4 L +
Volume (gases)
While the coefficients indicate the proportional relationships, only the mass and atoms are conserved in every chemical reaction

5. N2 (g) + 3 H2 (g) 2 NH3 (g) 1 mole + 3 moles 2 moles Molar Ratio: 1 N2
Conversion factor between parts of a chemical reaction.
1 N2
3 H2
3 H2
1 N2
1 N2
2 NH3
2 NH3
1 N2
3 H2
2 NH3
2 NH3
3 H2
There are 6 ratios that can be built from this equation to use as conversion factors depending on what is being compared

6. How many moles of H2 are used with 2 mol N2?
N2 (g) H2 (g)
2 NH3 (g)
1 N2
3 H2
2 mol N2
= 6 mol H2
*Make sure the equation is balanced
What you know
Add conversion factor
Units to cancel on bottom
Units in need on the top
Multiply top, divide bottom
What about moles of NH3 made?
1 N2
2 NH3
2 mol N2
= 4.0 mol NH3 (made)

7. Molar ratios – used to convert between compounds in a reaction…
How many moles of ammonia gas can be made from moles of hydrogen gas?
N2 (g) H2 (g)
2 NH3 (g)
0.350 mol H2
3 H2
2 NH3
= mol NH3 (made)
*Make sure the equation is balanced
What you know
Add conversion factor
Units to cancel on bottom
Units in need on the top
Multiply top, divide bottom
Molar ratios – used to convert between compounds in a reaction…

8. 2 Na(s) + Cl2(g) NaCl(s) 2 3.20 mol Cl2 2 NaCl 58.5 g NaCl
What mass of NaCl is formed from the reaction with 3.20 moles of chlorine gas? 2
Na(s) Cl2(g) NaCl(s) 2
3.20 moles
? g
NaCl = 58.5 g/mol
mol
3.20 mol Cl2
2 NaCl
58.5 g NaCl
= 374 g NaCl
1 Cl2
1 mol
STOICHIOMETRY
*Make sure the equation is balanced
What you know
Convert to moles
Use molar ratios to transition
Convert to desired units
Multiply top, divide bottom
We can skip step 2 here
– it started in moles

9. N2 (g) + H2 (g) NH3 (g) 3 2 15.0 g NH3 1 mol NH3 3 H2 = 1.32 mol H2
Calculate the moles of hydrogen needed to make
15.0 g of ammonia?
N2 (g) H2 (g) NH3 (g) 3 2
? mol
15.0 g
NH3 = 17.0 g/mol
mol
15.0 g NH3
1 mol NH3
3 H2
= 1.32 mol H2
17.0 g
2 NH3
STOICHIOMETRY
*Make sure the equation is balanced
What you know
Convert to moles
Use molar ratios to transition
Convert to desired units
Multiply top, divide bottom
Do this (I call it the “road map”) if you are struggling – show yourself the way before you start

10. What mass of carbon dioxide is produced from burning 50
What mass of carbon dioxide is produced from burning 50.0 g of ethane, C2H6?
C2H6 (g) O2 (g) CO2 (g) H2O (g) 2 7 4 6
50.0 g
? g
mol
mol
C2H6 = 30.0 g/mol
CO2 = 44.0 g/mol
50.0 g C2H6
1 mole C2H6
4 CO2
44.0 g CO2
30.0 g C2H6
2 C2H6
1 mole CO2
STOICHIOMETRY
*Make sure the equation is balanced
What you know
Convert to moles
Use molar ratios to transition
Convert to desired units
Multiply top, divide bottom
= 147 g CO2

11. FeS(s) + O2 (g) Fe2O3 (s) + SO2 (g) 7 2 4
How many grams of FeS are needed to make 36.3 g of Fe2O3? 4
FeS(s) + O2 (g) Fe2O3 (s) + SO2 (g) 7 2 4
? g
36.3 g
mol
mol
FeS = 87.9 g/mol
Fe2O3 = g/mol
36.3 g Fe2O3
1 mole Fe2O3
4 FeS
87.9 g FeS
159.6 g Fe2O3
2 Fe2O3
1 mole FeS
= g FeS

12. What volume of O2 is needed to make 19.8 L SO3?
SO2(g) + O2 (g) SO3 (g) 2
? L
19.8 L
mol
mol
19.8 L SO3
1 mole SO3
1 O2
22.4 L O2
22.4 L SO3
2 SO3
1 mole O2
= L O2
Maybe you have caught the trick here: since ALL gases at STP behave the same, we can just use the molar ratio to convert between litres of gas…

13. 2 Na(s) + Cl2 (g) NaCl (s) 2 = 4.87 L Cl2
What volume of chlorine gas is needed to react with 10.0 g of sodium? 2
Na(s) + Cl2 (g) NaCl (s) 2
10.0 g
? L
Na = 23.0 g/mol
mol
mol
10.0 g Na
1 mole Na
1 Cl2
22.4 L Cl2
23.0 g Na
2 Na
1 mole Cl2
= L Cl2
STOICHIOMETRY
*Make sure the equation is balanced
What you know
Convert to moles
Use molar ratios to transition
Convert to desired units
Multiply top, divide bottom

14. The energy change that occurs during a chemical reaction is called the Heat of Reaction:
Endothermic reactions – absorption of energy is required for the reaction to occur (reactant).
Exothermic reactions – energy is released as part of a spontaneous reaction (product).
A energy B
A B energy

15. Heat of reaction can be used just like ANY conversion factor…
What heat is produced from burning 60.0 g of ethane (C2H6), if the heat of combustion is 1560 kJ/mol of ethane?
C2H6 (g) O2 (g) CO2 (g) H2O (g) 2 7 4 6
60.0 g
mol
C2H6 = 30.0 g/mol
heat
60.0 g C2H6
1 mole C2H6
1560 kJ
= kJ
(energy released)
1 mole C2H6
30.0 g C2H6

16. 4 NH3 + 3 O2 2 N2 + 6 H2O + 300 kJ = 3000 g H2O 8000 kJ 6 mole H2O
What mass of water is produced in the reaction when 8000 kJ of energy is released?
4 NH3 + 3 O2 2 N2 + 6 H2O kJ
? g
8000 kJ
The heat is in the equation – you have to build a conversion factor…
mol
H2O = 18.0 g/mol
8000 kJ
6 mole H2O
18.0 g
= g H2O
300 kJ
1 mole H2O
IF you can find a relationship between ideas, you can solve!

17. Molar Ratio Exothermic Endothermic
CAN YOU / HAVE YOU?
C STOICHIOMETRY
Solve stoichiometric problems involving moles, mass, and volume, given the reactants and products in a balanced chemical reaction.
Include: heat of reaction
Identify the limiting reactant and calculate the mass of a product, given the reaction equation and reactant data.
Include: theoretical yield, experimental yield
Vocabulary & Concepts 
Molar Ratio Exothermic Endothermic