Mole Relations in Balanced Equations

Moles in Balanced Equations

Guide to solving for moles in balanced equations.

Given the reaction, 4Na + O2 → 2Na2O how many moles of oxygen are completely consumed in the production of 1.00 mol of Na2O?

1: First identify known and unknown.

Known: 4Na + O2 → 2Na2O

Known: 1.00 mol of Na2O (abbreviation of mole is mol)

Unknown: # mol of O2

2. Use balanced equation to determine mole ratio: 2 mol of Na2O: 1 mol of O2.

3. Set up equation: 1 mol of Na2O x = moles of O2.

4. Create fraction, from ratio, that will cancel unwanted units. In this case we want to cancel mol of Na2O therefore desired fraction is 1 mol of O2/2 mol of Na2O.

5. Final set-up and answer: 1 mol of Na2O x 1 mol of O2/2 mol of Na2O = ½ or 0.5 mol O2

1.  Given the reaction 4NH3 + 5O2 → 4NO + 6H2O, what is the maximum number of moles of H2O that can be produced when 2.0 mol of NH3 are completely reacted?

Known:

Unknown:

Ratio:

Set up equation:

Create fraction, from ratio, that will cancel unwanted units:

Final set up and answer:

2.  Given the reaction 2CH3OH(l) + 3O2(g) → 2CO2(g) + 4H2O(g), how many moles of O2 (g) are needed to produce exactly 20 mol of CO2(g)?

3.  Consider the following equation. CH4(g) + 2O2 → CO2(g) + 2H2O(g)

How many moles of oxygen are needed for the complete combustion of 3.0 mol of CH4(g)?

4.  According to the reaction 2Al + 3H2SO4 → 3H2 + Al2(SO4)3, the total number of moles of H2SO4 needed to react completely with 5.0 mol of Al is?

5.  Given the equation N2(g) + 3H2(g) → 2NH3(g), what is the total number of moles of NH3 produced when 10 mol H2 reacts completely with N2?

Challenge questions

6.  Given the reaction 2K(s) + Cl2(g) → 2KCl(s) what is the amount of K, in grams, needed to completely react with 2 moles of Cl2(g)?

7.  Consider the equation H2 + Cl2 → 2HCl. A student suggests that according to the ration shown by the coefficients, 20 g of hydrogen will react with 20 g of chlorine to form 40 g of HCl. Is the student correct? Explain.