Transcript Chemistry 103 - 001 - University of Nevada, Las Vegas

Chemistry 103
Lecture 15
Outline
I. Chemical Reactions
- balancing (review)
II. Stoichiometry
- Limiting Reactant
III. Classification of Reaction Types
Molar Mass from Periodic Table
Molar mass
• Is the atomic
mass
expressed in
grams
Avogadro’s Number

Solution = 6.022 x 1023

Avogadro’s number is equal
to 1 mole
Makes working with large numbers
easier

The Mole
Molar mass
Mass in grams
1 mole
6.022 x 1023
Individual particles
Concept Review

Do 7.0g of CO and 7.5 g of C2H6 contain the
same number of C atoms?
(Prove your answer mathematically)
A. YES
B. NO
Chemical Reaction
In a chemical reaction,
 Old bonds are broken and
new bonds are formed
 Atoms in the reactants are
rearranged to form one or
more different substances

Fe and O2 form rust (Fe2O3)
Chemical’s Shorthand - Chemical Rxn

Fe (s) + O2(g) --------> Fe2O3 (s)

2Fe(s) + O2(g) --------> Fe2O3(s)

4Fe(s) + O2(g) --------> 2Fe2O3(s)

4Fe(s) + 3O2(g) --------> 2Fe2O3(s)
BALANCED!!!!!

Balancing Practice

Li3N(s) -------> Li(s) +
N2(g)

Mg + H3PO4 ------> Mg3(PO4)2 + H2

MgCl2 + AgNO3 ------> Mg(NO3)2 + AgCl
Stoichiometry

Chemical Stoichiometry: using mass and quantity
relationships among reactants and products in a
chemical reaction to make predictions about how much
product will be made.
Moles in Equations
 We can read the equation in “moles” by placing the
word “mole” or “mol” between each coefficient and
formula.
4Fe(s)
+
4 mol Fe +
3O2(g)
2Fe2O3(s)
3 mol O2
2 mol Fe2O3
Mole to Mole problems

Using the balanced chemical reaction, how
many moles of O2 will react with 4.28 moles
of CS2 to produce CO2 and SO2?
CS2 + O2
------> CO2 + SO2 (unbalanced)
Mole to Mole problems

When 4.28 moles of CS2 reacts according to
the balanced chemical equation below, how
many moles of CO2 will be produced?
CS2 + 3O2
------> CO2 + 2SO2
Mole to Mole problems

When 4.28 moles of CS2 reacts according to
the balanced chemical equation below, how
many moles of SO2 will be produced?
CS2 + 3O2
------> CO2 + 2SO2
Reaction Interpretation

Using the balanced chemical reaction, how
many moles of O2 will react with 4.28 moles
of CS2 to produce CO2 and SO2?
CS2 + 3O2
BEFORE
AFTER
------> CO2 + 2SO2
Moles-to-Grams or Grams-to-Mole
Chemical Stoichiometry
2H2 + O2 ----> 2H2O
mole to mole comparisons:
How many moles of O2 are needed to produce
1.39 moles of H2O?
Chemical Stoichiometry
2H2 + O2 ----> 2H2O
mole to gram or gram to mole comparisons:
How many moles of O2 are needed to produce 7.4g
of H2O?
Chemical Stoichiometry
2H2 + O2 ----> 2H2O
mole to mole comparisons:
How many moles of O2 are needed to exactly react
with 4.28 moles of H2?
Chemical Stoichiometry
2H2 + O2 ----> 2H2O
mole to gram or gram to mole comparisons:
How many moles of O2 are needed to exactly react
with 12.4g of H2?
Grams-to-Mole
How many grams of O2 are needed to produce
0.400 mol Fe2O3?
4Fe(s)
+
3O2(g)
A) 38.4 g O2
B) 19.2 g O2
C) 1.90 g O2
2 Fe2O3(s)
“gram to gram” calculations
Calculating the Mass of a Reactant
The reaction between H2 and O2 produces 13.1 g water.
How many grams of O2 reacted?
2H2(g)
+ O2(g)
2H2O(g)
Plan: g H2O
mole H2O
mole O2
g O2
Calculating the Mass of a Reactant
The reaction between H2 and O2 produces 13.1 g water.
How many grams of O2 reacted?
2H2(g)
+ O2(g)
2H2O(g)
Before:
xg
After:
Plan: g H2O
13.1 g
mole H2O
mole O2
g O2
Mass calculations

How many grams of CS2 are needed to
completely react with 6.0g of O2 according to
the following reaction?

CS2 + 3O2 ------> CO2 + 2SO2
“gram to gram” continued….

One way to remove gaseous carbon dioxide from the air
in a spacecraft is to let canisters of solid lithium
hydroxide absorb it according to the following reaction:
2LiOH(s) + CO2(g) ------> Li2CO3(s) + H2O(l)
How many grams of LiOH must be used to produce
10.0g of Li2CO3?
Learning Check
Acetylene gas C2H2 burns in the oxyacetylene torch for welding. How
many grams of C2H2 are burned if the reaction produces 75.0 g CO2?
2C2H2(g) + 5O2(g)
A) 88.6 g C2H2
B) 44.3 g C2H2
C) 22.2 g C2H2
4CO2(g) + 2H2O(g)
Chemical Reactions
Limiting Reactant
&
Percent Yield
Limiting Reactant
A limiting reactant in a chemical reaction is the
substance that:
• Is used up first
• Stops the reaction
• Limits the amount of product that can form
Reacting Amounts
In a table setting, there is 1
plate, 1 fork, 1 knife, and 1 spoon.
How many table settings are
possible from 5 plates, 6 forks, 4
spoons, and 7 knives?
What is the limiting item?
Reaction Equivalent
1plate + 1fork + 1knife + 1spoon ----> 1place setting


BEFORE
5
6
7
4
0

AFTER
1
2
3
0
LR
4
Reacting Amounts
In a table setting, there is
1plate, 2 forks, 1 knife, and
1spoon.
How many table settings are
possible from 5 plates, 6 forks, 4
spoons, and 7 knives?
What is the limiting item?
Reaction Equivalent
1plate + 2fork + 1knife + 1spoon ----> 1place setting


BEFORE
5
6
7
4
0

AFTER
2
0
LR
4
1
3
Limiting Reactants
When 4.00 mol H2 is mixed with 2.00 mol Cl2,how many moles of HCl can
form?
H2(g) + Cl2(g)  2HCl (g)
4.00 mol
2.00 mol
??? Mol
STEPS:
•
Calculate the moles of product from each reactant, H2 and Cl2.
•
The limiting reactant is the one that produces the smallest amount of
product.
Checking Calculations
Initially
Reacted/
Formed
Left after
reaction
H2
Cl2
2HCl
4.00 mol
2.00 mol
-2.00 mol
-2.00 mol
0 mol
+4.00 mol
2.00 mol
Excess
0
mol
Limiting
4.00 mol
Limiting Reactant
If 4.80 grams Ca mixed with 2.00 grams N2,
which is the limiting reactant?
3Ca(s)
+ N2(g)
 Ca3N2(s)
Limiting Reactants Using Mass
Calculate the mass of water produced when 8.00 g H2
and 24.0 g O2 react?
2H2(g) + O2(g)
2H2O(l)