STOY-KEE-AHM-EH-TREE It's a big word that describes a simple idea. Stoichiometry: is the part of...
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Transcript of STOY-KEE-AHM-EH-TREE It's a big word that describes a simple idea. Stoichiometry: is the part of...
STOY-KEE-AHM-EH-TREE
It's a big word that describes a simple idea.
Stoichiometry: is the part of chemistry that studies amounts of substances that are involved in reactions OR… Simply the “math of chemistry”
You might be looking at the amount of material that is produced by the reaction.
You might be looking at the amounts of substances before the reaction
Stoichiometry is all about amounts.
PRACTICE BREAKDOWN: find the mass for these compounds
N2
NO2
2NH33(PO4) 3
14 + 14
28 grams
14 + 16 + 16
46 grams
14 + 1 + 1 + 1
17 grams
X’s 2 (the coefficient)
17 x 2= 34 grams
31 X 3= 93
285 grams
X’s 3 (the coefficient)
285 x 3= 855 grams
16X 12= 192
GOAL – to find the mass of the reactants and the products in a chemical reaction
Example: find the mass of each compound or molecule for the following equation
N2 + 3H2 --- > 2NH3
( Reactants ) ( Products )
28g
6g
34g
34g
Both sides
must be equal
5
11
2) set is up to CANCEL the unit that you want to get rid of
Ex: If you have 50 grams of Boron, how many moles do you have?
1 mole=11g50g 1 mole
1g 11g50 g
11g
4.5 moles=x =
Ex: If you have 80 grams of Sodium, how individual particles do you have?
1 mole=23g80g
1 mole 23g 23g=x =
481.6
23= 20.93913
Round to 20.9
Answer 1: 20.9 x 1023
Answer 2: 2.09 x 1024
11
23
Ex: If you have 7.8 moles of magnesium, how grams do you have?
1 mole=24g
1
7.8 mole
1 mole
7.8 x 24
1=x = 187.2grams
12
24
Producing a set quantity of a product using stoichiometry
Example: While working for Crest, you are instructed to generate 500grams of sodium flouride, how many grams of each of the reactants (Na & F) will you need?
Na + F2 -------- > NaF
Balance First! 2Na + F2 -------- > 2NaF
2Na + F2 -------- > 2NaF
46g
38g
84g
38g
84g
Step 1
Step 2 Find individual masses
2Na + F2 -------- > 2NaF
46g
38g
84g
Step 4 Find # to multiply by
Problem asked you to find how much using 500g of sodium fluoride…so figure out how many times 500 is in NaF and use that number to recalculate the rest
500g ÷84g = 5.95
38 x 5.95 46x 5.95
273.7g 226.1g
273.7 + 226.1g = 499.8 which rounds to 500
Step 5Check your work!
Producing a set quantity of a product using stoichiometry
Example: Based on the following problem, if an apple tree produces 800grams of sugar, how many grams of CO2 were used?
6CO 2 + 6H2O -------- > C6H12O6 + O 2
Looks alreadybalanced!
264g
108g
84g
92g 84g
Step 1
Step 2 Find individual masses
Sugar -
C6H12O6
6CO 2 + 6H2O ---- > C6H12O6 + 6O2
180g