Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections...
-
Upload
oscar-marsh -
Category
Documents
-
view
215 -
download
0
Transcript of Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections...
![Page 1: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/1.jpg)
StoichiometryQuantitative nature of chemical formulas
and chemical reactions
Chapter 3(Sections 3.3 - 3.7)
![Page 2: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/2.jpg)
Atomic Mass Scale• Atomic mass units (amu) are
convenient units to use when dealing with extremely small masses of individual atoms
• 1 amu = 1.66054 x 10-24 g• 1 g = 6.02214 x 1023 amu• By definition, the mass of C-12 is
exactly 12 amu
![Page 3: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/3.jpg)
Average Atomic Mass(Atomic Weight)
• We average the masses of isotopes using their masses and relative abundances to give the average atomic mass of an element.
• Naturally occurring C consists of 98.892% C-12 (12.00 amu) and 1.108% C-13 (13.00335 amu)
• The average mass of C is• (0.98892)(12.00 amu) + (0.01108)(13.00335)
= 12.01 amu • Atomic weights are listed on the periodic
table
![Page 4: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/4.jpg)
Calculating % Abundance• Chlorine is made up of two isotopes,
Cl-35 atomic mass = 34.969 amu and Cl- 37 atomic mass = 36.966 amu. Given chlorine’s atomic weight of 35.453, what is the % abundance of each isotope?
34.969(x) + (36.966) (1-x) = 35.45334.969x + 36.966 – 36.966x = 35.453x = .7576
75.76% Cl-35 and 24.24% Cl-37
![Page 5: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/5.jpg)
Formula & Molecular Weights
• Formula Weight is the sum of atomic weights for the atoms present in the chemical formula
• Molecular Weight is the sum of atomic weights of the atoms in a molecule as shown in the molecular formula
• Sample Exercise 3.5 page 80
![Page 6: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/6.jpg)
Percentage Composition from Formulas
• Obtained by dividing the mass contributed by each element (number of atoms times atomic weight) by the formula weight of the compound and multiplying by 100
• Sample Exercise 3.6 page 80
![Page 7: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/7.jpg)
The Mass Spectrometer page 81• Mass spectrometers are pieces of equipment designed to
measure atomic and molecular masses accurately.• The sample is converted to positive ions by collisions with a
stream of high-energy electrons upon entering the spectrometer.
• The charged sample is accelerated using an applied voltage.• The ions are then passed into an evacuated tube through a
magnetic field.• The magnetic field causes the ions to be deflected by
different amounts depending on their mass – more mass, less deflection.
• The ions are then detected.
![Page 8: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/8.jpg)
The Mole• The mole is a convenient
measure of chemical quantities. • 1 mole of something is 6.0221421
x 1023 of that thing.• This number is called
Avagadro’s number.• Thus 1 mole of carbon atoms =
6.0221421 x 1023 carbon atoms
![Page 9: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/9.jpg)
Molar Mass• mass in grams of 1 mole of a
substance• expressed in units of g/mol• formula weights are numerically
equal to the molar mass • Sample Exercise 3.8 page 84
![Page 10: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/10.jpg)
Interconverting Masses, Moles, & Number of Particles
• To convert between grams and moles, we use the molar mass
• To convert between moles and particles (atoms, molecules, or ions) we use Avogadro’s number
• Sample Exercises 3.7, 3.9, 3.10, 3.11 pages 82-86
![Page 11: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/11.jpg)
Empirical Formula• Gives the relative number of
atoms of each element in the substance
• Can be calculated from mass percent data
• Sample Exercise 3.12 page 87
![Page 12: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/12.jpg)
Molecular Formula• Actual number of atoms of
each element in one molecule of the substance
• Whole number multiple of empirical formula
• Sample Exercise 3.13 page 88
![Page 13: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/13.jpg)
Combustion Analysis• A sample containing C, H,
and O is combusted in excess oxygen to produce CO2 & H2O
• Can be used to determine empirical formula or percent composition
![Page 14: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/14.jpg)
Quantitative Information from Balanced Equations
• Coefficients can be interpreted as the relative numbers of molecules or formula units in the reaction as well as the relative number of moles
• See Figure 3.14 page 92• Sample Exercises 3.14, 13.15
pages 92 & 93
![Page 15: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/15.jpg)
Limiting Reactant(s)• The reactant(s) that is completely consumed in
a reaction• Limits or determines the amount of product
that will be formed• The other reactant(s) that is left over is called
the excess reactant • Sample Exercise 3.16 and 3.17 pages 95-96• How much of the excess reactant is left over?
![Page 16: Stoichiometry Quantitative nature of chemical formulas and chemical reactions Chapter 3 (Sections 3.3 - 3.7)](https://reader036.fdocuments.in/reader036/viewer/2022082611/56649e185503460f94b03d46/html5/thumbnails/16.jpg)
Percent Yield (actual yield / theoretical yield) X 100
• Actual is the amount of product recovered in the lab
• Theoretical is the amount predicted from stoichiometry
• Sample Exercise 3.18 page 97