2. The recipe
● 200 g sugar
● 113.5 g butter
● 2 eggs
● 180 g flour
● 7 g baking powder
● 113.5 g milk
In a recipe, proportions among the ingredients are fundamental and they allow us
to calculate the necessary quantities to cook/bake as much food as needed.
¿How many eggs are needed to bake 6 muffins? ¿How many moles of sugar?
(sacarose: C12H22O11)
¿How many muffins can we bake with 1 kg of flour? ¿How many L of milk are needed?
(⍴leche = 1,030 g·mL-1)
¿How much baking powder should I use with 2,3 kg of butter?
12 muffins
3. Summary
200 g sugar
113.5 g butter
2 eggs
12 muffins
180g/12
180 g flour
7 g baking powder
113.5 g milk
Muffin
Sugar
BkPwd
Flour
Egg
Milk Butter
2/12
2/7g
4. Stoichiometric* coefficients represent the proportions among
reactants and product and allow us to calculate any quantities
involved in a chemical reaction
Stoichiometric coefficients
*derived from the Greek words stoicheion, meaning element, and metron, meaning measure
5. Symbolic representation of a chemical reaction
Chemical equations
Stoichiometric
coefficients
Chemical formula
Aggregate state
Reaction arrow
Reactants Products
8. Put it all together!
m
(g)
V
(L)
Vds
(L)
mds
(g)
B
(mol)
A
(mol)
D
(mol)
C
(mol)
9. Stoichiometry
Conceptual Problems
1. How does a balanced chemical equation agree with the law of conservation of matter?
2. What is the difference between S8 and 8S? Use this example to explain why subscripts in a formula must not be
changed.
3. What factors determine whether a chemical equation is balanced?
4. What information can be obtained from a balanced chemical equation? Does a balanced chemical equation
give information about the rate of a reaction?
5. If 2 mol of sodium reacts completely with 1 mol of chlorine to produce sodium chloride, does this mean that 2 g
of sodium reacts completely with 1 g of chlorine to give the same product? Explain your answer.
Numerical Problems
1. Balance each chemical equation.
a. KI(aq) + Br2(l) → KBr(aq) + I2(s)
b. MnO2(s) + HCl(aq) → MnCl2(aq) + Cl2(g) + H2O(l)
c. Na2O(s) + H2O(l) → NaOH(aq)
d. Cu(s) + AgNO3(aq) → Cu(NO3)2(aq) + Ag(s)
e. SO2(g) + H2O(l) → H2SO3(aq)
10. 2. Answer the following questions about this reaction:
2H2+ O2 → 2H2O
a. ¿How many hydrogen molecules are needed to react with 48 oxigen molecules? R: 96 molec H2
b. If you performed the reaction and got 5 moles of water, ¿with how many moles of O2 and H2 would you
have started with?
R: 2.5 mol O2, 5 mol H2
a. If you started with 37,5 g of O2, ¿how many grams of H2 would you need? R: 4.73 g H2
Stoichiometry
3. Barium chloride and sodium sulfate react to produce sodium chloride and barium sulfate.
If 50.00 mL of 2.55 M barium chloride is used in the reaction, how many grams of sodium
sulfate are needed for the reaction to go to completion?
4. How many grams of sodium phosphate are obtained in solution from the reaction of 75.00 mL
of 2.80 M sodium the third, CO2. How many grams of the third product are obtained?
3. How many grams of ammonium bromide are produced from the reaction of 50.00 mL of 2.08
M iron(II) bromide with a stoichiometric amount of ammonium sulfide? What is the second
product? How many grams of the second product are produced?
R: 18.105 g Na2SO4
R: Grams of CO2: 9.24 g, Grams of Na2SO4: 22.26g
R: Grams Produced: 20.37 g NH4Br2, Second Product: Iron (II) Sulfide, 9.15 g FeS
