Calculate the amount of CO2 that is produced when a)1 mol C is burned in air, b)1 mol C is burned in 16 g O2, and c)2 mol C are burned in 16 g O2.
This is a stoichiometry problem, so you must have a balanced equation. I generally write the equation, balance it, then write the quantities (the given one(s) and use ? for what you are being asked) below the substances, and write the the molar masses (from the periodic table) above the substances.
a) 12 g/mol 32 g/mol 44 g/mol (molar masses)
C + O2 —→ CO2 (balanced, no coefficients needed)
1 mol ? (given, asked)
To do stoichiometry, you will use the mol ratio of two substances in the balanced equation, such as these
examples:
1 mol CO2 1 mol O2 1 mol CO2 1 mol C
1 mol C 1 mol C 1 mol O2 1 mol O2
In this problem, the conversion factor will be a ratio of a reactant to a product , such as: 1 mol CO2
1 mol C
Use dimensional analysis with the conversion factor from the balanced equation:
1 mol C x 1 mol CO2 = 1 mol CO2 (which can be converted from mol → g , if needed)
1 mol C
b) In this next case, you will have an one more calculation step (a conversion), in addition to that shown
above:
12 g/mol 32 g/mol 44 g/mol (molar masses)
C + O2 —→ CO2 (balanced equation)
1 mol 16 g ? (given, asked)
You already determined that 1 mol of C (with excess O2) will produce 1 mol CO2, so now you must determine how much CO2 will be produced from 16 g O2. Whichever reactant, 1 mol C or 16 g O2, makes the least amount of product is the limiting reactant, which determines how much product is made from the quantities given.
Convert the O2 quantity from g → mol, then do the stoichiometry:
16 g O2 x 1 mol O2 = 0.50 mol O2
32 g O2
0.5 mol O2 x 1 mol CO2 = 0.5 mol CO2 (which can be converted from mol → g , if needed)
1 mol O2
Since this is less than the amount of product you can make from 1 mol C, the O2 is the limiting reactant upon which any calculations must be based.
Therefore, given 1 mol C and 16 g O2 you can make 0.5 mol CO2.
c) For the last part of the problem, you must determine how much product you can make using 2 mol C
and compare that calculated quantity with the previous calculation based on 16 g O2.
12 g/mol 32 g/mol 44 g/mol (molar masses)
C + O2 —→ CO2 (balanced equation)
2 mol 16 g ? (given, asked)
2 mol C x 1 mol CO2 = 2 mol CO2
1 mol C
From 2 mol C you can make 2 mol CO2 and from 16 g O2 you can make 0.5 mol CO2 ; therefore, the O2 is the limiting reactant, and the calculated amount of product must be based on the quantity of O2 given, not the quantity of C given, which you did in the previous part of this problem.
From 2 mol C and 16 g O2, therefore, you can produce 0.5 mol CO2.