A. Representative Particle Level Mass-Mass Relationships in a Chemical Reaction Consider the following reaction between sodium metal and solid sulfur: 2 K(s) + S(s) = K2S(s) Two sodium atoms react with one sulfur atom to form one sodium sulfide formula unit.
average mass of a potassium atom = 6.493 x 10^-23 g
average mass of a sulfur atom = 5.324 x 10^-23 g
average mass of a potassium sulfide formula unit= 1.831 x 10^-22 g
Mass relationships between representative particles in reactions can be determined just like mass relationships between single nuts, bolts, or bolt/nut combinations as illustrated on the last sheet.
Solve the following representative particle relationship problems. A solution to the first is provided as an example.
1. About what mass of sulfur atoms is needed to completely react with about 2.5756 x 10^-22g of potassium atoms? Ans. __________
2. About what mass of potassium atoms is needed to react with about 4.259 x 10^-22g of sulfur atoms? Ans. __________
To determine the amount of products and reactants that are produced or needed in a given reaction.
Quantitative relationship between the number of moles of various products and reactants in a chemical reaction. (reaction must be balanced).
3. If about 1.282 x 10^-21g of potassium sulfide formula units are formed, how many grams of sulfur reacted (solve by stoichiometry, rather than percent composition!)? Ans. __________
To solve these representative particle relationship problems, we need to use stoichiometry, which is a method of calculating the quantities of reactants and products involved in a chemical reaction. In this case, we will be using the average masses of the atoms and formula units provided to determine the masses involved in the reactions.
1. About what mass of sulfur atoms is needed to completely react with about 2.5756 x 10^-22g of potassium atoms?
We are given the average mass of a potassium atom (6.493 x 10^-23 g) and the average mass of a sulfur atom (5.324 x 10^-23 g). The balanced equation tells us that 2 potassium atoms react with 1 sulfur atom to form 1 potassium sulfide formula unit.
To find the mass of sulfur atoms needed, we can set up a proportion using the molar masses:
(2.5756 x 10^-22 g K) / (6.493 x 10^-23 g K) = (x g S) / (5.324 x 10^-23 g S)
Cross-multiplying and solving for x (mass of sulfur):
x = (2.5756 x 10^-22 g K) * (5.324 x 10^-23 g S) / (6.493 x 10^-23 g K)
x ≈ 2.1189 x 10^-22 g
So, about 2.1189 x 10^-22 g of sulfur atoms is needed to completely react with about 2.5756 x 10^-22 g of potassium atoms.
2. About what mass of potassium atoms is needed to react with about 4.259 x 10^-22g of sulfur atoms?
Using the same approach as above, we can set up a proportion using the molar masses:
(4.259 x 10^-22 g S) / (5.324 x 10^-23 g S) = (x g K) / (6.493 x 10^-23 g K)
Solving for x:
x = (4.259 x 10^-22 g S) * (6.493 x 10^-23 g K) / (5.324 x 10^-23 g S)
x ≈ 5.1993 x 10^-22 g
So, about 5.1993 x 10^-22 g of potassium atoms is needed to react with about 4.259 x 10^-22g of sulfur atoms.
3. If about 1.282 x 10^-21g of potassium sulfide formula units are formed, how many grams of sulfur reacted?
In this case, we need to use stoichiometry to find the mass of sulfur that reacted. From the balanced equation, we know that 2 potassium atoms react with 1 sulfur atom to form 1 potassium sulfide formula unit.
First, we can calculate the number of moles of potassium sulfide formula units formed:
moles of K2S = (1.282 x 10^-21 g K2S) / (1.831 x 10^-22 g K2S)
Next, we can use the stoichiometric ratio to find the number of moles of sulfur:
moles of S = moles of K2S * (1 mol S / 1 mol K2S)
Finally, we can convert the moles of sulfur to grams:
mass of S = moles of S * molar mass of S
Using the average mass of a sulfur atom (5.324 x 10^-23 g), we can calculate the mass of sulfur that reacted.
Keep in mind that the molar mass of Sulfate in that compound is multiplied by 2 due to the coefficient in the balanced equation: K2S(s).
Thus, the detailed calculation is:
moles of K2S = (1.282 x 10^-21 g K2S) / (1.831 x 10^-22 g K2S) = 6.996 mol K2S
moles of S = 6.996 mol K2S * (1 mol S / 1 mol K2S) = 6.996 mol S
mass of S = 6.996 mol S * (5.324 x 10^-23 g S / 1 mol S) X 2= 7.441 x 10^-22 g
So, about 7.441 x 10^-22 g of sulfur reacted to form about 1.282 x 10^-21 g of potassium sulfide formula units.