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Calculations from Chemical Equations

Learn about stoichiometry and how to perform mole-mole, mole-mass, and mass-mass calculations using balanced chemical equations. Master the art of converting units and ratios for accurate results.

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Calculations from Chemical Equations

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  1. Stoichiometry Calculations from Chemical Equations Mole-Mole Calculations Mole-Mass Calculations Mass-Mass Calculations Thursday, March 1st, 2018

  2. What is stoichiometry? Stoichiometry is the quantitative study of reactants and products in a chemical reaction.

  3. What is stoichiometry?

  4. What You Should Expect • Given : Amount of reactants • Question:how much of products can be formed. • Example • 2 A + 2B  3C • Given 20.0 grams of A and sufficient B, how many grams of C can be produced?

  5. What do you need? You will need to use • molar ratios, • molar masses, • balancing and interpreting equations, and • conversions between grams and moles. Note: This type of problem is often called "mass-mass."

  6. Stoichiometry • Stoichiometry: calculations based on a balanced chemical equation • Mole ratio: ratio of coefficients of any two substances in a balanced chemical equation A mole ratio converts moles of one compound in a balanced chemical equation into moles of another compound.

  7. Example Reaction between magnesium and oxygen to form magnesium oxide. ( fireworks) 2 Mg(s) + O2(g) 2 MgO(s) Mole Ratios: 2 : 1 : 2

  8. The Goal The goal of stoichiometry is to perform conversions (changing between units) by cancelling out units until you end up with the units you want (the answer).

  9. 1 mol = molar mass 1 mole = 22.4 L @ STP 1 mol = 6.02 x 1023 particles Welcome to Mole Island

  10. Stoichiometry Island Diagram Known Unknown Substance A Substance B M Mass Mass Mountain Mass Mole Island Volume Mole Mole Volume V Liter Lagoon Particles Particles P Particle Place Stoichiometry Island Diagram

  11. Stoichiometry Island Diagram Known Unknown Substance A Substance B Mass Mass 1 mole = molar mass (g) 1 mole = molar mass (g) Use coefficients from balanced chemical equation Volume Mole Mole Volume 1 mole = 22.4 L @ STP 1 mole = 22.4 L @ STP (gases) (gases) 1 mole = 6.022 x 1023 particles (atoms or molecules) 1 mole = 6.022 x 1023 particles (atoms or molecules) Particles Particles Stoichiometry Island Diagram

  12. 4 mol O2 1 x Mole-Mole Calculations • How many moles of water can be obtained from the reaction of 4 moles of O2? 2 H2 (g) +1O2 (g) → 2 H2O (g) 2 mol H2O 1 mol O2 = 8 mol H2O Mole Ratio

  13. 8 mol H2 1 x • How many moles of NH3 can be obtained from the reaction of 8 moles of H2? __ H2 (g) + __ N2 (g) → __ NH3 (g) 3 1 2 2 mol NH3 3 mol H2 = 5.33 mol NH3 Mole Ratio

  14. 6 mol Al 1 x x Mole-Mass Calculations 2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g) • What mass of hydrogen gas can be produced by reacting 6 moles of aluminum with HCl? 3 mol H2 2 mol Al 2.0 g H2 1 mol H2 = 18 g H2 Mole Ratio Molar Mass

  15. 6 mol Al 1 x x 2 Al (s) + 6 HCl (aq) → 2 AlCl3 (aq) + 3 H2 (g) • What mass of HCl is needed to react with 6 moles of aluminum? 6 mol HCl 2 mol Al 36.0 g HCl 1 mol HCl = 648 g HCl Mole Ratio Molar Mass

  16. Mass-Mass Calculations Sn(s) + 2 HF (g) → SnF2 (s) + H2 (g) How many grams of SnF2 can be produced from the reaction of 30.00 g of HF with Sn? 1 molSnF2 2 mol HF 156.71 g SnF2 1 mol SnF2 30.00 g HF 1 1 mole HF 20.01 g HF x x x = 117.5 g SnF2 Molar Mass Molar Mass Mole Ratio

  17. Steps Involved in Solving Mass-Mass Stoichiometry Problems • Balance the chemical equation correctly • Using the molar mass of the given substance, convert the mass given to moles. • Construct a molar proportion (two molar ratios set equal to each other) • Using the molar mass of the unknown substance, convert the moles just calculated to mass.

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