Chapter 8: Stoichiometry

1. Interpreting chemical equations
2. Mole-mass calculations
3. Mass-mass calculations
4. Other stoichiomentric  calculations
5. Limiting reactant
6. Percent yield [ Practice Theoretical Yield] [Practice Percent Yield]
7. Energy changes [Practice ]
8. Heat of reaction [Reference] [Practice]

 Chapter 8

8-1 Interpreting Chemical Equations

- Information about particles, moles, mass, and volume can all be derived from a chemical equation.

8-2 Mole-Mole Calculations

- Example: How many moles of table salt are formed when .3 moles of sodium react with an unlimited supply of chlorine?

 - Start with the equation: 2Na + Cl2 ---------> 2NaCl

 - Set up true relationships:

 .3 mol Na  x  2 mol NaCl  =  .3 mol NaCl
                     2 mol Na

8-3 Mass-Mass Calculations

- Mass-Mass Calculations are the same as mol-mol calculations except for two added steps: reactant mass -> moles and product moles -> mass.

8-4 Other Stoichiometric Calculations

- True relationships can be used to solve any stoichiometric problem.

8-5 Limiting Reagent

- Let's say we have 400 slices of bread and 14 bananas. We want to make as many banana sandwiches as we can. At first, you might think that since we have 400 slices of bread, we can make 200 sandwiches. But we only have 14 bananas! The small number of bananas we have limits us to 14 sandwiches. Bananas is the limiting reagent (reactant) in this example.

- Notice that in the example in section 8-2, I said that .3 moles of Na react with an unlimited supply of chlorine. Adding the "unlimited" makes it clear that sodium is the limiting reactant. If I hadn't said that, it could have been possible that there were only 2 chlorine atoms. Were that the case, the .3 moles of Na surely couldn't have been all used, making the amount of product considerably lower. That is why knowing the limiting reactant in stoichiometric problems is so important.

8-6 Percent Yield [ Practice Theoretical Yield] [ Practice Percent Yield]

- Doing chemistry problems stoichiometrically assumes there will be no error in the reaction. Of course this is not true, so the concept of percent yield must be introduced. Do a chemistry problem stoichiometrically, do it experimentally, and then figure out the percent yield:

 - Percent yield =     actual yield (experimental)      x  100%
                           theoretical yield (stoichiometric)

8-7 Energy Changes in Reactions [Practice]

- Exothermic = heat is released. Example: X + Y            > XY+ 498 joules

- Endothermic = heat is absorbed. Example: MN + 21 joules              > M + N

- Thermochemical equation = chemical equation with heat as product or reactant (like above examples).

- Energy diagrams show heat being absorbed or released as a reaction progresses.

- Exothermic:

- Endothermic:

8-8 Heat of Reactions [Reference] [Practice]

- Enthalpy = the heat a substance has.

- D H = "delta H" = change in enthalpy.

- The D H for a reaction in which 1 mol of a compound is formed from its elements is that compounds standard heat of formation (D H°¦)

- See Chempire's Online Heat of Formations Chart for standard heat of formations. -------LLLLLLLLLIIIIIIIIINNNNNNNNNNNKKKKKKKKK----------

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