25. Composition stoichemisrty- composition stoichemistry describes the quantitative
relationships among elements in compounds. It can be used to determine the number of atom
present in a collection of molecules and the masses of each. For example, composition
stoichiometry describes the nitrogen to hydrogen (mass) relationship in the compound ammonia:
ie., one mole of nitrogren and three moles of hydrogen are in every mole of ammonia.
26. Reaction stoichemistry- describes the quantitative relationships among substances as they
participate in chemical reactions. An example is when reaction stoichiometry describes the 1:3:2
ratios of molecules of nitrogen, hydrogen, and ammonia.
27. mole ratio- The coefficients in a balanced equation can be used to write a molar ratio. Molar
ratios are conversion factors that can be used to relate:
1. moles of product formed from a certain number of moles of reactant
2. moles of reactant needed to form a certain number of moles of a product.
3. the number of moles of a particular reactant needed to completely react with a certain number
of moles of a second reactant.
For the following reaction:
4 NH3 (g) + 5 O2 (g) --> 4 NO (g) + 6 H2O (g)
the following molar ratios can be written:
4 moles NH3
4 moles NH3
4 moles NH3
5 moles O2
4 moles NO
6 moles H2O
5 moles O2
5 moles O2
4 moles NO
4 moles NO
6 moles H2O
6 moles H2O
28. mole ratio- You need the balanced symbol equation for the reaction. The numbers in front of
the formulae show the mole ratios. For example, in the thermal decomposition of calcium
carbonate:
CaCO3 --> CaO + CO2
The equation is balanced.
The mole ratio between CaCO3 and CO2 is 1:1 because there is 1 mole of CaCO3 for every
mole of CO2
29. Mole A > mole B Ratio (pg. 360)
Example: How many mole of water are made when 16.4 mol of Oxygen are used?
First you have to use the 5 Step methods: Given, Find, Plug In, and Solve.
And the Bala
Given: 16.4 mol of Oxygen
Find: moles of water
Plug In/ Solve: 16.4 mol O2
1
x 2 mol H2O
= 32.8 mol H2O
1 molO2
30- 31. Gram A > gram B Ration (pg. 361 their will be two problems)
Example: Calculate the number of grams of NH3 produced by the reaction of 54.0g of hydrogen
with an excess of nitrogen.
First you have to use the 5 Step methods: Given, Find, Plug In, and Solve.
And the Balanced Equa
Given: 54.0g H2, 3molH2 (From Balanced Equation), 1 mol H2 (molar mass), and
1 mol NH3= 17.0 (molar mass)
Molar Mass: H2
H2: 1.01 x 2= 2.0
Molar Mass: NH3
N: 14.0 x 1= 14.0
H3: 1.01x 3= 3.0
= 17.0
Find: mass of ammonia= gNH3
Plug In/ Solve: 54.0 x 1mol H2 x 2.0 mol NH3 x 17.0 gNH3 = 31g NH3
2.0 gH2
32. Mol A > gram B (pg. 370)
3.0 mol H2
1 mol NH3
Example: What is the maximum number of grams of Cu2S that can be formed when 80.0 g Cu
reacts with 25.0 g S? which is limiting?
First you have to use the 5 Step methods: Given, Find, Plug In, and Solve.
And Convert “givens” to moles:
Given: 80gCu, 25.0gS
Find: which is limiting
80gCu x 1 molCu
1
63.55gCu
25.0gS x 1molS
1
= 1.26 molCu
= 0.78 molS
32.06
Plug In/ Solve:
1.26 molCu x 1molS
1
= 0.63 molS
2molCu
Copper Is Limiting
33) Limiting Reactant- The reagent that determines the amount of product that can be formed by
a reaction. Example: NH3, the limiting reactant would be hydrogen because it is completely used
up.
34) Excess reactant- The reactant that is not completely used up in a reaction. Example: NH3, the
excess reactant would be nitrogen because it is not entirely used up.
35) mol A mol B
Mole Ratio- A conversion factor derived from the coefficients of a balanced chemical equation
interpreted in terms of moles.
1) Find the balanced equation
2) State the given
3) State what you need to find
4) Use the mole-mole calculations to solve (Given x mole ratio= Answer)
36) G A mol B
1) Find the balanaced equation
2) State the given
3) State what you need to find
4) Find the molar mass of the given
5) Use the mole-mole calculations to solve
37) Finding the limiting reactant
Limiting Reactant- The reagent that determines the amount of product that can be formed by a
reaction.
1) State the two given
2) Find the balanced equation
3) Find the molar mass of each given, you will have two answers
4) Use the statement, “How many of __(have)___ would I need to use up all the _(need)__.”
(This will help determine if your answer will be excess or limiting)
5) Use the mole-mole calculations to solve
6) If your answer is more than what you “have” your answer will be excess, therefore the other
answer will be stated as “limiting”