know the difference between physical and chemical changes and be able to identify changes in substan

1
Chemical Reactions and Quantities Goals
At the end of this chapter you should

• know the difference between physical and
  chemical changes and be able to identify changes
  in substances into the appropriate category.
• Know the concept of a mole and the relationship
  between number of particles, moles and Avogadros
  number.
• Know how to calculate the molar mass of a
  substance and how to use molar mass in chemical
  calculations.

2
Chem. Reac. and Quant. the difference between
physical and chemical changes
Properties
Physical
Chemical
can be measured without changing the chemical
nature (its identity) of the element.
Color Size Density Boiling point Melting point
Properties that DO change the chemical nature of
matter Reactivity Combustion
3
Chem. Reac. and Quant. the difference between
physical and chemical changes
In a physical change, the identity and
composition of the substance do not change.
In a chemical change, reacting substances form
new substances with different compositions and
properties.
4
Chem. Reac. and Quant. chemical changes and
chemical equations

• A chemical equation gives the chemical formulas
  of the reactants on the left of the arrow and the
  products on the right.
• Reactants
  Product

5
Chem. Reac. and Quant. The mole

• A collection term states a specific number of
  items.
• 1 dozen donuts 12 donuts
• 1 ream of paper 500 sheets
• 1 case 24 cans
• Similarly a mole is a collection that contains
  6.02 x 1023 particles (either atoms, ions or
  molecules)
• the same number of particles as the number of
  carbon atoms in 12.0 g of carbon.
• 6.02 x 1023 - Avogadros number.
• 1 mole element
  Number of Atoms
• 1 mole C 6.02 x 1023 C atoms
• 1 mole Na 6.02 x 1023 Na atoms
• 1 mole Au 6.02 x 1023 Au atoms
• 1 mole molecule Number of
  Molecules
• 1 mole H2O 6.02 x 1023
  water molecules
• 1 mole CO2 6.02 x 1023
  carbondioxide molecules

6
Chem. Reac. and Quant. The mole as an equality

• Avogadros number 6.02 x 1023 can be written as
  an equality and two conversion factors.
• Equality
• 1 mole 6.02 x 1023 particles
• Conversion Factors
• 6.02 x 1023 particles and 1
  mole
• 1 mole 6.02 x 1023 particles
• Avogadros number is used to convert moles of a
  substance to particles.
• How many Cu atoms are in 0.50 mole Cu?
• 0.50 mole Cu x 6.02 x 1023 Cu atoms
• 1 mole Cu
• 3.0 x 1023 Cu atoms

7
Chem. Reac. and Quant. Moles and chemical
formulas

• The subscripts in a formula show
• the relationship of atoms in the formula.
• the moles of each element in 1 mole of compound.
• Glucose C6H12O6
• In 1 molecule of glucose 6 atoms C 12
  atoms H 6 atoms O
• In 1 mole of glucose 6 mole C 12 mole H
  6 mole O
• Conversion factors
• 6 mole C 12 mole H
  6 mole O
• 1 mole glucose 1 mole glucose 1
  mole glucose
• 1 mole glucose 1 mole glucose 1
  mole glucose
• 6 mole C 12 mole H
  6 mole O

8
Chem. Reac. and Quant. Moles and molar mass
For a reaction in my lab I need 1 mole of copper.
How do I go about measuring this
quantity? Although I know that 1 mole of Cu has
6.02 x 1023 Cu atoms that does not really help
me. Need some way to relate 1 mole of Cu to a
measurable quantity such as mass.

• The molar mass
• is the mass of one mole of an element or
  compound.
• is the atomic mass expressed in grams.

9
Chem. Reac. and Quant. Moles and molar mass

• The molar mass of a compound is the sum of the
  molar masses of the elements in the formula.
• Example Calculate the molar mass of CaCl2.
• Element Number of Moles Atomic Mass Total Mass
• Ca 1 40.1
  g/mole 40.1 g
• Cl 2
  35.5 g/mole 71.0 g
• CaCl2
  111.1 g
• We can use molar masses of elemetns and compounds
  to write conversion factors.

10
Chem. Reac. and Quant. Moles and molar mass
Calculate the molar masses of these,
(1). MgSO4 - tocolytic agent -
(2). C6H6O6 - Glucose -
(3). C18H34O2 - oleic acid (in olive oil) -
(4). C21H26O5 - prednisone, anti-inflammatory -

11
Chem. Reac. and Quant. Moles, molar mass, and
conversion factors

• Molar mass conversion factors
• are written from molar mass.
• relate grams and moles of an element or compound.
• Example Write molar mass factors for methane,
  CH4, used in gas stoves and gas heaters.
• Molar mass 1 mol CH4 16.0 g
• Conversion factors
• 16.0 g CH4 and 1 mole CH4
• 1 mole CH4 16.0 g CH4

Moles
Grams
12
Chem. Reac. and Quant. Moles, molar mass,
particles and Avogadros number

• A molar mass factor and Avogadros number convert
• grams to particles and particles to grams
• g mole
  particles

molar mass
Avogadros number
Try these,
(1). How many grams are in 2.25 moles each of
the following NaBr, C6H14
(2). How many moles are in 4.00 g of Ca(NO3)2?
13
Chem. Reac. and Quant. Moles and chemical
reactions

• The Law of Conservation of Mass indicates that in
  an ordinary chemical reaction,
• Matter cannot be created nor destroyed.
• No change in total mass occurs in a reaction.
• Mass of products is equal to mass of reactants.