Science - Raines, Charlena
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Stoichiometry – Multi Step Conversions
- Stoichiometry is the calculation of quantities in chemical reactions.
- When you know the quantity of one substance in a reaction, you can calculate the quantity of another substance consumed or created in the reaction.
- A quantity can be grams, moles, liters, molecules, atoms, ions, formula units or particles.
- Theoretical yield is the maximum amount of product that will form during a reaction. (how much you expect to make)
- Example: 1 box of muffin mix says it will make 12 muffins
- Any time you are calculating the amount of product produced you are calculating theoretical yield.
- Actual yield is the amount of product that actually forms when the reaction is carried out in a laboratory.
- Example: when used the 1 box of muffin mix only makes 11 muffins (instead of the 12 it theoretically should have made).
- Stoichiometry Calculations General Steps
- The first step is to convert the give substance measurement to moles. (if not starting with moles)
- Next use the mole ratio to switch between substances
- Finally convert to the desired substance to the correct unit for the final answer.
- Remember:
- 1 mol = (molar mass) grams
- RECAL: molar mass is the SUM of ATOMIC MASSES
- 1 mol = 22.4 Liters
- 1 mol = 6.02 x 1023 particles (ptl)
- _____ mol A = ____ mole B [called the mole ratio]
- These are the ONLY conversion you can do.
- 1 mol = (molar mass) grams
- Things to remember
- Don’t let the words in the problem confuse you. If it doesn’t have a number or a unit it probably is not important. Especially when given the complete chemical equation.
- You MUST have a balanced chemical equation to do ANY mole to mole conversions.
- The coefficients in the balanced chemical reaction are used in the mole ratio ONLY
- Mole ratios are the ONLY place that you can switch substances.
- Can NOT do this [], you can only go from gram to mole, volume to mole, particles to mole
- The starting amount (# given in the problem) is only written ONE time, and never in a conversion fraction.
- Any time you have a reactant in excess it does NOT affect calculations (you can ignore it)
- Some students find using the mole map helpful
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- Video Examples
- Mass to mass: https://www.youtube.com/watch?v=2Q8HtHItjxI
- Mass to Particles: https://www.youtube.com/watch?v=XzitAFr5POE
- Mass & liters: https://www.youtube.com/watch?v=bRM2g50kBHI
- GPB Series:
- Chemistry Matters
- http://www.gpb.org/chemistry-matters/unit-6/a [basics of dimensional analysis]
- http://www.gpb.org/chemistry-matters/unit-6/b [mole and Avagadro's number.]
- http://www.gpb.org/chemistry-matters/unit-6/c [moles to liters]
- http://www.gpb.org/chemistry-matters/unit-6/d [stoichiometric calculations and mole ratios]
- Chemistry
- http://www.gpb.org/chemistry-physics/chemistry/801 [mole-mole & mole-mass]
- http://www.gpb.org/chemistry-physics/chemistry/802 [mass-mass & percent yield]
- Chemistry Matters