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The Mole And Moler Mass
Conversation of mass
Mole Coversation
Molar Mass And Conversion Prob
Mole Conversion
Stoichemistry
Stoicheometry
Molar Conversion
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| Stoichiometry |
| What is Stoichiometry? |
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What is Stoichiometry?-------------------------------------------------------------------------------- The Meaning of the Word The word stoichiometry derives from two Greek words: stoicheion (meaning "element") and metron (meaning "measure"). Stoichiometry deals with calculations about the masses (sometimes volumes) of reactants and products involved in a chemical reaction. It is a very mathematical part of chemistry, so be prepared for lots of calculator use. What You Should Expect The most common stoichiometric problem will present you with a certain amount of a reactant and then ask how much of a product can be formed. Here is a generic chemical equation: 2 A + 2B ---> 3C Here is a typically-worded problem: Given 20.0 grams of A and sufficient B, how many grams of C can be produced? You will need to use molar ratios, molar masses, balancing and interpreting equations, and conversions between grams and moles. If you struggled with those in class, welcome to the club. Go back and review them if you need to, because if you can't do that stuff, you can't do stoichiometry. This type of problem is often called "mass-mass." The Steps Involved in Solving Mass-Mass Stoichiometry Problems Make sure the chemical equation is correctly balanced. Using the molar mass of the given substance, convert the mass given in the problem to moles. Construct a molar proportion (two molar ratios set equal to each other) following the guidelines set out in other files. Use it to convert to moles of the unknown. Using the molar mass of the unkown substance, convert the moles just calculated to mass. ------------------------------------------------------------------ Molar Ratio-------------------------------------------------------------------------------- The molar ratio will assume a place of central importance in solving stoichiometry problems. The sources for these ratios are the coefficients of a balanced equation. We will look at what a molar ratio is and then a brief word on how to recognize which ratio to use in a problem. The ChemTeam's favorite sample equation is: 2 H2 + O2 ---> 2 H2O What is the molar ratio between H2 and O2? Answer: two to one. So this ratio in fractional form is:  The ChemTeam recommends you explicitly write a one in the denominator of the ratio. -------------------------------------------------------------------------------- What is the molar ratio between O2 and H2O? Answer: one to two. As a fraction, it is:  You knew that, of course. The ChemTeam apologizes if you felt like you were being treated like a dummy! -------------------------------------------------------------------------------- What is the molar ratio between H2 and H2O? Answer: two to two or:  As you well know, this reduces to one to one. However, the ChemTeam will use the unreduced fraction in the lessons to follow. -------------------------------------------------------------------------------- Here's another example equation: 2 O3 ---> 3 O2 The exact molar ratio you would use depends on how the problem is worded. What is the molar ratio between O3 and O2? What is the molar ratio between O2 and O3? The first one, of course, is:  And the second simply reverses the numbers:  -------------------------------------------------------------------------------- Before looking at the practice problems, an important point: the coefficients of a reaction only give the ratio in which substances react. They do not in any way tell you HOW MUCH is reacting. This point is elaborated upon in what the ChemTeam believes is the next logical unit from here. However, do the problems first! -------------------------------------------------------------------------------- Practice Problems Following each equation are two requests for molar ratios from the equation. 1) N2 + 3 H2 ---> 2 NH3 Write the molar ratios for N2 to H2 and NH3 to H2. 2) 2 SO2 + O2 ---> 2 SO3 Write the molar ratios for O2 to SO3 and O2 to SO2. 3) PCl3 + Cl2 ---> PCl5 Write the molar ratios for PCl3 to Cl2 and PCl3 to PCl5. 4) 4 NH3 + 3 O2 ---> 2 N2 + 6 H2O Write the molar ratios for NH3 to N2 and H2O to O2. 5) Fe2O3 + 3 CO ---> Fe + 3 CO2 Write the molar ratios for CO to CO2 and Fe to CO. ----------------------------------------------------------- Answers1) N2 + 3 H2 ---> 2 NH3Molar Ratio N2 to H2 NH3 to H2 2) 2 SO2 + O2 ---> 2 SO3 Molar Ratio O2 to SO3 O2 to SO2 3) PCl3 + Cl2 ---> PCl5 Molar Ratio PCl3 to Cl2 PCl3 to PCl5 4) 4 NH3 + 3 O2 ---> 2 N2 + 6 H2O Molar Ratio NH3 to N2 H2O to O2 5) Fe2O3 + 3 CO ---> 2 Fe + 3 CO2 Molar Ratio CO to CO2 Fe to CO |
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