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Stoichiometry is a powerful tool that all chemist must utilize. It separates the scientists from everyone else. It allows a chemist to determine an amount of another compound that is needed or produced in a chemical reaction.
Question- How many grams of water can be produced from 10.grams of H2 with excess O2? excess=you have more than enough O2 to complete this reaction, worry about H2 1. You need a balanced chemical reaction. 2H2 + O2 ==> 2H2O (remember that the coefficients are really mole ratios) 2. FIND THE MOLES of your compound. Sometimes it is already given, sometimes you have to calculate it. Given==> 10. grams of H2 Find the moles=> 10.g H2 (1mol / 2.0g H2)= 5.0 mol H2 3. DO THE RATIO-Now you can find the moles of any other compound in this reaction using the coefficients of the balanced reaction. Here are a few ways to do this. Factor Label 5.0 mol H2 ( 2 mol H2O /2 mol H2) =5.0 mol H2O or set up a proportion
x= 5.0 mol H2O or set up an equation proportion (remember that the coefficients are really mole ratios)
Now you solved for O2 also(2.5 mol) and H2O (5.0 mol) 4. ANSWER THE QUESTION-Now find the mass from the number of moles 5.0 mol H2O ( 18.0g/mol)= 90. g H2O
If I wanted to know about the O2, I could just take the moles and find the mass. 2.5 mol O2 ( 32.0g/mol)= 80. g O2 FYI the mass in equals the mass out.
Conclusion- Find the moles, do the ratio, answer the question On to Limiting Stoichiometry |
