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Stoichiometry

Stoichiometry begins with balanced equations, which are essential for solving chemical problems. Always ensure your equation is balanced—if not, balance it using coefficients (not subscripts). For example, in the reaction of magnesium and sulfur (Mg + S → MgS), one mole of each reacts to produce one mole of magnesium sulfide. This principle extends to complex reactions, where you can use stoichiometry equivalents as conversion factors. Moreover, consider limiting reagents and yield calculations to determine the efficiency of chemical reactions, distinguishing theoretical yield from actual yield.

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Stoichiometry

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  1. Stoichiometry

  2. Balanced Equations • All stoichiometry problems start with a balanced equation. • You must check for this! • If it is not balanced, BALANCE IT!

  3. Reviewing Balancing Equations S Fe Fe2S3 S Fe S • Can change coefficients but CANNOT change subscripts • Example • 3S + 2 Fe  Fe2S3

  4. Reviewing Balancing Equations • Al + CuO Al2O3 + Cu • ____________________________

  5. Reviewing Balancing Equations • H2 + O2 H2O _______________________

  6. Equations and the Mole • Remember what an equation actually means • Mg + S  MgS • One __________reacts with one ________creating one formula unit of ___________ • But • This also means that one ___________________reacts with one ________________ to form one ________________ formula units. • 1 mol Mg, 1 mol S, and 1 mol MgS are stoichiometry equivalents

  7. Equations and the Mole (cont) • What about the equation • C3H8 + 5O2 3CO2 + 4H2O • Now, ___ mol C3H8, ____ mol O2, ___ mol CO2, and _____ mol H2O are stoichiometry equivalents

  8. What does this mean? • As stoichiometry equivalents, they can be used in a conversion factor • __________________ Conversion Factors • One equivalent is placed on top and one on bottom • Allows us to move from one compound to another in a balanced equation

  9. Stoichiometry Problems Given the equation: MgCl2 + 2 AgNO3 Mg(NO3)2 + 2 AgCl What is the mass of AgCl produced if 24g of MgCl2 is reacted with excess AgNO3? What amount of MgCl2 will react with 3.85 g AgNO3?

  10. Limiting Reagents • So far we have been assuming that we have an excess of all the other reactants • This is not often true….often you have a set amount of both reactants • Each amount would lead you to a different amount of product • Must use the number that is ___________

  11. Limiting Reagent Problem Given the equation: MgCl2 + 2 AgNO3 Mg(NO3)2 + 2 AgCl How much AgCl will be produced if 28g of MgCl2 is reacted with 51g of AgNO3?

  12. Theoretical and Actual Yield • Yield is the amount of product that you get from a reaction • _________________ yield is the amount that you should get based on using stoichiometry • ______________ yield is the amount of product actually attained during an experiment

  13. % Yield • Calculated by taking • _____________________________________

  14. Theoretical and % Yield Given the equation: MgCl2 + 2 AgNO3 Mg(NO3)2 + 2 AgCl What is the percent yield of Mg(NO3)2 if 168.4 g of AgNO3 is reacted to produce 47.2g of Mg(NO3)2?

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