Chapter Five

Chemical Quantities and Reactions








The Mole
Molar Mass
Chemical Changes
Chemical Equations
Types of Reactions
Mole Relationships in Chemical Equations
Mass Calculations
Energy in Chemical Reactions



Many things have names for a quantity or group.
In chemistry, a quantity of atoms, molecules, etc. is called a mole.


Why a “mole”?

The Mole




A mole of anything is 6.02 E+23 particles.
This is sometimes referred to as
Avogadro’s Number.
Written as a number:

602,000,000,000,000,000,000,000
A mole of marbles would easily fill the entire Grand Canyon with much to spare.

The Mole

One mole of:




Carbon = 6.02 E+23 carbon atoms
CO
2
=6.02 E+23 CO
2 molecules
NaCl = 6.02 E+23 NaCl formula units
1 mole of anything = 6.02 E+23 particles
1 mole of anything
6 .
02

10
23 particles or
6.02

10
23 particles
1 mole of anything

Learning Check

Ex) Convert 0.0242 moles of CH
4 molecules. to

Learning Check

Ex) Convert 4.45 E+21 atoms of Zn to moles.

Subscripts and Moles


The subscripts in a formula can be interpreted on either an atom or mole level.
Ex) C
6
H
12
O
6

Learning Check

Ex) How many moles of H atoms are present in 0.0150 moles of NH
How many H atoms?
3
?

Molar Mass


A molar mass of an element is the atomic mass expressed in grams.
The molar mass of carbon is
12.01g

Molar Mass


The molar mass of any compound is equal to the sum of all the atomic weights for each element in the formula.
Ex) The molar mass of CO
2 is:
1C + 2O = 1(12.0g) + 2(16.0g) = 44.0g
Thus, 1 mole of CO
2
= 44.0g

Learning Check
 a)
What is the molar mass of MgCl
2
94.0g
?
b)
59.8g
c) d)
95.3g
119.6g

Learning Check
 a)
What is the molar mass of Al(OH)
3
?
78.0g
b)
46.0g
c) d)
132.0g
44.0g

Molar Mass


Any molar mass can written as a conversion factor.
From earlier:

1 mole of CO
2
= 44.0g
1 mole CO
2
44 .
0 g
44.0
g or
1 mole CO
2

Molar Mass


This allows for the conversion between grams and moles.
Ex) 45.0g of BaCl
2
= ? moles

Molar Mass

Ex) 1.52 x 10 -3 moles of phosphorous tribromide = ? grams

Moles

Combining both molar mass and
Avogadro’s number concepts.

Learning Check

An 8.15 E+21 molecules of C
2 would have a mass of:
H
6

Learning Check

A 45.3g sample of lead(II) chloride would contain how many formula units?

Learning Check

A 6.50 x 10 atoms?
-5 g sample of C
5
H
10
O will contain how many Hydrogen
5

Physical Changes

A physical change is one in which the state, shape, or size of the substance is altered but not its identity.




Ex) Ice melting
Ex) Ripping a piece of paper
Ex) Boiling ethanol
Ex) Pulverizing a rock

Chemical Changes

A chemical change is one in which matter is transformed into new kinds of matter by the rearrangement of atoms.




Ex) Iron rusting
Ex) Burning a log
Ex) Fermenting grapes
Ex) Antacid neutralizing stomach acid

Learning Check

Decide whether each is Physical or
Chemical change.



 a) Making Kool-aid b) Baking cookies c) Cutting an aspirin in half d) Bleaching a stained shirt

Chemical Equations

Shows the before and after for a chemical reaction using chemical formulas.

Chemical Equations

Symbols added having various meanings.

Chemical Equations



A Chemical Equation is always written so that the total numbers of atoms on each side of the equation are equal.
To do this, coefficients are added in front of each substance.
Must use lowest whole number coefficients!

Chemical Equations




__Al + __Cl
2
 __AlCl
3
Reaction is NOT balanced!
Note: can NOT alter any subscripts!
Make a tally sheet.

Learning Check

Balance the following:

__FeCl
2
+ __Al  __AlCl
3
+ __Fe

__Al
2
(SO
4
)
3
+ KOH  Al(OH)
3
+ K
2
SO
4

Learning Check

Balance the following:

__H
3
PO
3
 __H
3
PO
4
+ __PH
3

__C
3
H
8
+ __O
2
 __CO
2
+ __H
2
O

Learning Check

Balance the following:

__C
4
H
8
O + __O
2
 __CO
2
+ __H
2
O

Types of Reactions

Combination Reaction


2Al(s) + 3Br
2
(l)  2AlBr
3
(s)
CaO(s) + CO
2
(g)  CaCO
3
(s)

Types of Reactions

Decomposition Reaction

(NH
4
)
2
Cr
2
O
7
(s)  Cr
2
O
3
(s) + 4H
2
O(g) + N
2
(g)


Single Replacement Reactions

Mg(s) + CuCl
2
(s)  MgCl
2
(s) + Cu(s)


Double Replacement Reactions

Pb(NO
3
)
2
(aq) + K
2
CrO
4
(aq)  PbCrO
4
(s) + 2KNO
3
(aq)

Combustion


A rapid reaction with oxygen from the air.

CH
4
(g) + 2O
2
(g)  CO
2
(g) + 2H
2
O(l)
Also occurs in the cells of animals when glucose, C to energy.
6
H
12
O
6
, is converted

Chemical Reactions

A reaction can be interpreted in many ways.



Atoms and molecules
Moles
Masses

Chemical Reactions


N
2
+ 3 H
2
 2 NH
Molecular interpretation
3

Mole interpretation

Mass interpretation



In any chemical reaction, matter cannot be created nor destroyed.
Masses of reactants = Masses of products.

N
2
15 molecules
H
2
2.4 moles
NH
3
0.014 moles

Stoichiometry


The calculation of chemical quantities in a reaction.
Relates a mass of a reactant or product to any other reactant or product.

Stoichiometry
Mass of A
Mass of B
Moles of A Moles of B

Stoichiometry

If 45.1g of N
2 mass of H
2 are used, then what is required?


45 .
1 g N
2
















Stoichiometry

If 7.25g of H
2 completely reacts, what mass of NH
3 is produced?


7 .
25 g H
2
















Stoichiometry


For the reaction:

2C
2
H
2
+ 5O
2
 4CO
2
+ 2H
2
O
If 6.85g of C
2
H
2 is completely combusted, then what mass of CO
2 is produced?
 a. 13.7g


 b. 11.6g
c. 23.2g
d. 5.80g

Stoichiometry


For the reaction:

4Al + 3O
2
 2Al
2
O
3
When 0.452g of Al completely reacts, what mass of Al
2
O
3 is produced?
 a. 3.42g


 b. 0.853g
c. 0.226g
d. 23.1g


Collision Theory

In the game of pool (billiards), in order to sink a ball in the pocket what is needed?

In reactions, what is needed?

Activation Energy

The activation energy is the minimum amount of energy required to produce a reaction.



Reactions that release heat energy are said to be ________________.
Reactions that absorb heat energy are said to be ________________.



Energy level of the products is lower than that of the reactants.
Heat is a product and can be included in the balanced reaction.
Ex) C( s ) + 2H
2
(g)

CH
4
( g ) + 18 kcal



Energy level of the products is higher than that of the reactants.
Heat is a reactant.
Ex) N
2
( g ) + O
2
( g ) + 43.3 kcal

2NO( g )



Reactions can range from instantaneous (very fast) to very slow.
We can affect the rate of reaction by:

Increasing the concentration of the reactants.

Rate of a Reaction


Increasing the temperature of the reactants. This increases the fraction of molecules that have enough energy to react.
Adding a catalyst. A catalyst lowers the activation energy.

2
2(aq)

2
(l)
2(g)