2 Reactant A + Reactant B --> 2 Product C + Product D
Example: 2 H2 + O2 --> 2H2O
- In the reaction above, compounds A and B react to produce compounds C and D.
- The coefficients show us that 2 moles of compound A are needed to react completely with 1 mole of compound B. When these ratios are followed, 2 moles of compound C and 1 mole of compound D are produced.
- Mole ratios can be written to represent numerical relationships between any two compounds in a chemical reaction. The following ratios can be written for the reaction above:
- 2 mole A : 1 mole B
- 2 mole A : 2 mole C
- 2 mole A : 1 mole D
- 1 mole B : 2 mole C
- 1 mole B : 1 mole D
- 2 mole C : 1 mole D
- Mole ratios are conversion factors that can be used in dimensional analysis. We can rewrite the ratios in a fraction form.
- 2 mole A : 1 mole B is the same as 2 mole A / 1 mole B or 1 mole B / 2 mole A
- Identify the given compound and unknown compound in a word problem, and use those two compounds in your mole ratio.
- Begin dimensional analysis by writing the given compound and draw the dimensional analysis chart. Insert the identified mole ratio as a fraction. Place the portion of the ratio containing the given compound in the denominator to cancel.
If 3.1 moles of H2 are used in the reaction, how many moles of O2 are needed to react completely?
NOTE: H2 is the given compound, and O2 is the unknown compound. Therefore, we'll use the mole ratio between H2 and O2 in the balanced equation.