PARTICLES1. You can calculate the quantities of reactants and products in a reaction from a balanced equation.
2. Stoichiometry is the calculation of quantities in chemical equations.
8.1 Interpreting Everyday Equations.
1. Balanced equation is like a recipe.
2. Can determine products and ingredients.
3. Example 1 and 2, probs 1&2.
8.2 Interpreting Chemical Equations
1. N2(g)+3H2(g)--->2NH3 (g)
PARTICLES2. Ratio of 1:3:2 ratio of molecules and moles.
3. Also 1x avagadros number N2 with 3 x avagadros number H2 yields 2 x avagadros number of ammonia molecules.
MOLES4. The coefficients of a balanced equation give you the relative numbers of moles of reactants and products in the chemical reaction.
MASS5. A balanced chemical equation must obey the law of conservation of mass.
6. 1 mol nitrogen = 28.0 g plus 3 mol of hydrogen = 6.0 g yields 2 mol ammonia = 34.0 g.
VOLUME7. 1 mol of any gas at STP is 22.4 L. Equation gives information about each reactant and product.
8. See figure 8.2
9. Only mass and number of atoms are always conserved. Representative particles, moles, volume may not be.
10. Example 3
8.3 Mole-Mole Calculations
1. N2(g)+3H2(g)--->2NH3 (g)
2. From number of moles can determine conversion factors.
3. 1:3:2, factors: 1:2, 1:3, etc.
4. You can calculate the number of moles of product from given number moles of reactant.
5. Using other mole-quantity relationships, can introduce mass, volume, and particles.
6. Example 4, 5
7. Note that mole ratios (from coefficients) are exact numbers.
8. Problem 7
8.4 Mass-Mass Calculations
1. From the mass of a reactant or product, you can calculate the mass of any other reactant or product in a given chemical equation.
2. First change mass of A to moles of A. Then change moles of B for moles of A. Then find mass of B.
3. Example 6, 7
8.5 Other Stoichiometric Calculations
1. Balanced chemical equations give the relative number of moles of each reactant and product. From this we can go from any related quantity: volume, particles, mass.
2. Convert given quantity to moles. Use mole ratio to find moles of wanted substance. From moles of wanted substance, we can convert to any other measurement.
3. Example 8: Calculating Moles of a Product.
4. Example 9: Finding the volume of a gas.
5. The coefficients in a balanced chemical equation tell you the relative number of moles. The coefficients also indicate the relative volumes of interacting gases.
6. The volume can be expressed in any unit: cm3, dm3, ml, liters, etc.
7. Exampes 9, 10. Prob 14, 15
8.6 Limiting Reagent
1. Limiting reagent limits or determines the amount of product that can be formed in a reaction.
2. Excess reagent is more than enough.
3.Example 11.
Start with
known amount of one reactant and find amount of other reactant necessary
to react.
Determine which
is limiting reagent.
Use limiting
reagent to calculate amount of product produced.
Use limiting
reagent to calculate actual amount of 1st reactant.
Determine excess.
8.7 Percent Yield
1. When an equation is used to calculate the amount of product that will form during a reaction, a value for the theoretical yield is obtained. This is the maximum amount of product that could be formed.
2. The amount of product that forms when the reaction is carried out in the laboratory is called the actual yield.
3. The actual yield is often less than the theoretical yield. The percent yield is the ration of the actual yield to the theoretical yield expressed as a percentage.
4. Many factors cause percent yields to be less than 100%:
Reactions do
not go to completion
Impure reactants
and competing side reactions may cause other products to form.
Some of the product
may be lost during filtration or transferring.
6. Example 13, prob 22, 23.