powerpoint to accompany chapter 2 part 1 stoichiometry: calculations with chemical formulae and...
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PowerPoint to accompany
Chapter 2Part 1
Stoichiometry:Calculations with
Chemical Formulae and Equations
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Law of Conservation of MassFigure 2.1
“We may lay it down as an incontestable axiom that, in all the operations of art and
nature, nothing is created; an equal amount of matter
exists both before and after the experiment. Upon this principle, the whole art of
performing chemical experiments depends.”
--Antoine Lavoisier, 1789
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Chemical Equations
Concise representations of chemical
reactions.
They mainly give proportions phases
They do not imply mechanism
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Figure 2.4 *
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Reactants appear on the
left side of the equation.
Note that the equation contains molecules or elements and the phases they exist in during the reaction. e.g. Methane (gas)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Products appear on the right side of the equation.
The Arrow indicates which direction the reaction tends to go. If it points both ways it signifiies equilibrium.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Anatomy of a Chemical Equation
The states of the reactants and products
are written in parentheses to the right of
each compound. In this example all are gases.
*
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Anatomy of a Chemical Equation
CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
Coefficients are inserted tobalance the equation.
Balanced Equations have the same elements
and numbers of atoms of each element on both sides
of the equation.
Numbers of Molecules are proportionate to
a complete reaction, not absolute.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Subscripts and Coefficients Give Different Information
Subscripts indicate the number of atoms of each element in a molecule
Coefficients indicate the number of molecules
Figure 2.2
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Reaction Types: *Combination:
A + B C
Decomposition:
A B + C , often with a gas
Combustion:
Fuel + Oxidant Ash, Gases
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Examples N2 (g) + 3 H2 (g) 2 NH3 (g)
C3H6 (g) + Br2 (l) C3H6Br2 (l)
2 Mg (s) + O2 (g) 2 MgO (s)
Combination Reactions
Two or more substances react to form one product:
A+BC
Figure 2.5 *
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Examples N2 (g) + 3 H2 (g) 2 NH3 (g)
C3H6 (g) + Br2 (l) C3H6Br2 (l)
2 Mg (s) + O2 (g) 2 MgO (s)
Combination Reactions Nitrogen gas reacts with hydrogen gas to
form ammonia gas (Nitrogen fixation). Cyclopropane gas reacts with liquid bromine
to form 1,5 dibromopropane Magnesium metal reacts with oxygen gas to
form solid magnesium oxide.
Figure 2.5
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
2 Mg (s) + O2 (g) 2 MgO (s)
Combination Reactions Figure 2.5 *
48.61 g Mg + 32.00 g O2 = 80.61 g MgO
What happens if you only have 16 g of O2 ?
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Decomposition Reactions
One substance breaks down into two or more substances
Examples CaCO3 (s) CaO (s) + CO2 (g) 2 KClO3 (s) 2 KCl (s) + 3 O2 (g)
2 NaN3 (s) 2 Na (s) + 3 N2 (g)
2 NaN3 (s) 2 Na (s) + 3 N2 (g)
Figure 2.6 *
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Decomposition Reactions
One substance breaks down into two or more substances
Sodium azide solid reacts to form sodium metal and nitrogen gas. (So what does it mean if somebody
text’s you: “ U NaN3 “ ?)
2 NaN3 (s) 2 Na (s) + 3 N2 (g)
Figure 2.6
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Decomposition Reactions
One substance breaks down into two or more substances
Calcium carbonate (limestone) decomposes to form solid unslaked lime and carbon dioxide gas.
This is the 1st step to make portland cement.
CaCO3 (s) CaO (s) + CO2 (g)
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Decomposition ReactionsOne substance breaks down into two or more substances
2 KClO3 (s) 2 KCl (s) + 3 O2 (g)
POP QUIZ!
2 moles of solid _______decomposes to form
2 moles of solid _ _ and 3 moles of gas.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Decomposition ReactionsOne substance breaks down into two or more substances
2 KClO3 (s) 2 KCl (s) + 3 O2 (g)
POP QUIZ!
2 moles of solid Potassium Chlorate decomposes to form
2 moles of solid Potassium Chloride and3 moles of Oxygen gas.
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Combustion Reactions Rapid reactions that
produce a flame
Most often involve hydrocarbons reacting with oxygen in the air
Examples CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g)
Figure 2.7
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Combustion ReactionsMost often involve hydrocarbons reacting with oxygen in the air
Which hydrocarbon fuel generates the least amount of greenhouse gas?
Examples CH4 (g) + 2 O2 (g) CO2 (g) + 2 H2O (g)
C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g)
Figure 2.7
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Formula Mass
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Formula Mass ( or Weight)
Sum of the atomic weights of the atoms in a chemical formula
The formula mass of calcium chloride, CaCl2, would be
Ca: 1 x 40.1 g = 40.1 g
+ Cl: 2 x 35.5 g = 71.0 g
111.1 g
According to Dalton’s Law what would the decomposition of 1 mole of Calcium Chloride generate?
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Molecular Mass
Sum of the atomic weights of the atoms in a molecule
For the molecule ethane, C2H6, the molecular weight would be
C: 2 x 12.0 g = 24.1 g + H: 6 x 1.0 g = 6.0 g
30.1 g
For the complete combustion of 1 mole of ethane, what weight of water would be produced?
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Mass of Water from Ethane
For the complete combustion of 1 mole of ethane, what weight of water would be produced?
C2 H 6 (g) 2 CO2 (g) + 3 H2O (g) .
6 g H makes 3 moles of H2O,
each mole of water is 1 mole of Oxygen for 16 g and 2 moles of Hydrogen for 2 g, so 18 g.
But there are 3 moles of water so:
3 moles water X 18 g/mole = 54g water
Brown, LeMay, Bursten, Murphy, Langford, Sagatys: Chemistry 2e © 2010 Pearson Australia
Percent Composition
One can find the percentage of the mass of a compound that comes from each of the elements in the compound by using this equation:
% element =(number of atoms of that element)x(atomic mass of that element)
(formula mass of the compound)x 100
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