1. Chemical Calculations
Section 12.2

2. Review
We have previously learned how to balance chemical equations and how to interpret those balanced equations in terms of different chemical quantities.
A balanced equation is ESSENTIAL for all calculations involving amounts of reactants and products.
A balanced chemical equation allows you to determine the number of moles of ALL substances in the reaction.

3. Writing and Using Mole Ratios
What is a ratio?
It is one number divided by another. A proportional relationship between two quantities.
What is a mole ratio?
It is a conversion factor derived from the coefficients of a balanced chemical equation.

4. Examples of Mole Ratios
N2 + 3H2  2NH3
Six mole ratios can be derived:
1 𝑚𝑜𝑙 𝑁2 3 𝑚𝑜𝑙 𝐻 𝑚𝑜𝑙 𝑁2 2 𝑚𝑜𝑙 𝑁𝐻 𝑚𝑜𝑙 𝐻2 2 𝑚𝑜𝑙 𝑁𝐻 𝑚𝑜𝑙 𝐻2 1 𝑚𝑜𝑙 𝑁 𝑚𝑜𝑙 𝑁𝐻3 1 𝑚𝑜𝑙 𝑁 𝑚𝑜𝑙 𝑁𝐻3 3 𝑚𝑜𝑙 𝐻2
Let’s practice setting up our table. Remember the extra credit?

5. Do your own example:
4Al + 3O2  2Al2O3
Write the six mole ratios that can be derived from this equation.
Let’s practice setting up that table.

6. Chemical Calculations
There are 4 types of calculations we are going to learn about today.
1. Mole-Mole Calculations
2.Mass-Mass Calculations
3.Calculating Molecules of a Product
4.Volume-Volume Calculations

7. Calculation 1 Mole-Mole Calculations Page 360
N2 + 3H2  2NH3
How many moles of ammonia are produced when mol of nitrogen reacts with hydrogen?
Step 1: Known: 0.60 mol N2
Step 2: Unknown: Amount of ammonia ????
Step3: Set Up table, fill in values, complete conversion problem.

8. Calculation 2 Mass-Mass Calculations Page 361
N2 + 3H2  2NH3
Calculate the number of grams of NH3 produced by the reaction of 5.40g of hydrogen with an excess of Nitrogen.
Step 1: Knowns: Mass of Hydrogen= 5.40g
Step 2: Unknowns: Mass of Ammonia ?????
Step 3: Set Up table, fill in values, complete conversion problem.

9. Using your current table…
How many moles of NH3 are produced if 50g of N2 react with excess H2?
How many grams of H2 is needed to form 18 moles of NH3?
How many moles of N2 need to react to form 10 moles of NH3?
How many grams of NH3 is formed if 15.0 g of N2 is used?

10. Practice
Page 360 # 11 b
Page 361 # 13

11. In conclusion:
Your table can be used to calculate between moles, grams, and between grams and moles in ONE step.
What if I needed other info such as VOLUME and NUMBER OF MOLECULES? One more step…

12. Calculation 3 Calculating Molecules of a Product Page 364
How many molecules of oxygen are produced when 29.2g of water is decomposed by electrolysis (separation by electricity) according to this balanced equation?
2H2O(l)  2H2(g) + O2(g)
Step 1: Knowns:
Mass of Water = 29.2g
Step 2: Unknown: Molecules of O2 ????
Step 3: Set up conversion problem using table. 1 extra step.

13. Calculation 4 Volume-Volume Calculation Page 365
2NO + O2  2NO2
1 mole = 22.4L
Nitrogen monoxide and oxygen gas combine to form the brown gas nitrogen dioxide, which is part of SMOG. Yuck! How many liters of nitrogen dioxide are produced when 34L of oxygen reacts with an excess of NO? Assume STP!
Step 1: Known: Volume of oxygen= 34L O2
Step 2: Unknown: Volume of NO2 in Liters ???
Step 3: Set Up partial table, complete conversion with your extra steps. Remember: 1 mole of any gas at STP= Liters

14. Practice
Page 365 # 17
Page 364 # 15

15. In SUMMARY
For Mole-Mole, Mass-Mass, Mole-Mass, and Mass-Mole, set up a full table to complete these conversions.
For Number of Molecules: Set up table. Add extra step of
1 mole=6.02x1023 molecules.
For Volume-Volume, use PARTIAL table and add your two extra steps of 1 mole = 22.4L.

16. In-Class Practice Something to think on:
For this chapter, practice is how we are going to get better at these. Please offer suggestions of things we can do that you think will further your understanding or make it more interesting.
Page 360 #12 a and b
Page 361 #14
Page 364 # 16
Page 366 #23, 24
YOU HAVE ALREADY MADE TABLES FOR SOME OF THESE PROBLEMS!
There will be an open-note mini quiz on these concepts. You will be able to use these 4 problems on the quiz if you complete them!