Transcript Diapositiva 1

Warm Up: Jan. 13th
• Answer these on Ch. 8.1 Notes
1. What is the EMPIRICAL formula
for a substance that is 63.52% iron
and 36.48% sulfur?
2.
Succinic acid's empirical formula is
C2H3O2. the molar mass is 118.09 g,
what is the molecular formula?
Chapter 8
Chemical Equations and reactions
Ch. 8.1 Intro to Chemical RXNs
 A chemical reaction is the process by which one
or more substances are changed into one or
more different substances.
 In any chemical reaction, the original
substances are known as the reactants and the
resulting substances are known as the
products.
 A chemical equation represents, with symbols
and formulas, the identities and relative
amounts of the reactants and products in a
chemical reaction.
– Example: The following chemical equation shows
that the reactant ammonium dichromate yields the
products nitrogen, chromium(III) oxide, and water.
(NH4)2Cr2O7  N2 + Cr2O3 + 4 H2O
– The arrow () is used to separate the reactants
from the products. (Read as “produces” or
“yields”)
• What causes a chemical reaction to occur?
 mixing substances
 adding energy to a substance (heat/electric
current)
4 Indicators of a Chemical Reaction
1. Evolution of energy as heat and
light
2. Production of a gas
3. Color change
4. Formation of a precipitate.
• A solid that is produced as a result of a
chemical reaction in solution and that
separates from the solution is known as a
precipitate.
Ch. 8.2 Law of Conservation of Mass
•
Atoms are neither created nor destroyed in
ordinary chemical reactions. (just rearranged)
•
Same number of atoms of each element must
appear on both sides of the equation.
•
In order for an equation to correctly describe a
reaction, it must be “balanced.”
• Coefficient – number placed in front of a
symbol or formula to balance the
equation.
– Do not confuse with subscript.
• Example:
H 2 + O2 
H 2O
2 H 2 + O2  2 H 2O
• Never alter a subscript when trying to
balance a chemical equation. Why?
Balancing Chemical Equations
 Most chemical equations can be balanced by inspection.
(Insert coefficients as needed.)
 Examples:
Zn + HCl  ZnCl2 + H2
N2 + H2  NH3

However, some equations can be more difficult to
balance.
 Some helpful hints:
 Balance polyatomic ions that appear on both sides of the
equation as single units.
 Atoms listed more than one time on a side should be
balanced last.
 Examples:
AlBr3 + K2SO4  KBr + Al2(SO4)3
CH4 + O2  H2O + CO2
Ch. 8.3 Word Equations
• Sometimes the reactants and products
in a chemical reaction are given in
words.
– You must convert into chemical formulas
before you can balance the equation.
• There are seven elements that occur in
nature as diatomic molecules.
Elements That Normally Exist as
Diatomic Molecules
Element
Formula
Hydrogen
H2
Nitrogen
N2
Oxygen
O2
Fluorine
F2
Chlorine
Cl2
Bromine
Br2
Iodine
I2
Some Examples (balanced)
1. magnesium + oxygen  magnesium
oxide
2. potassium iodide + lead (II) nitrate 
potassium nitrate + lead (II) iodide
Symbols Used in Chemical Equations
Other Symbols Used in Chemical Equations
Some Example Equations
1. Iron metal in chlorine gas reacts to
form solid iron (III) chloride.
2. Aqueous solutions of barium chloride
and sodium chromate react to produce
a precipitate of barium chromate and
an aqueous solution of sodium
chloride.
15
Your turn
1. Convert the following word equations
into formula equations and balance.
a) When heated, solid aluminum carbonate
decomposes to form solid aluminum oxide and
carbon dioxide gas.
b) Hydrogen gas and iron (III) oxide powder react to
form liquid water and iron powder.
16
Reflection
• You have one minute to answer these two questions
concerning today’s lesson.
– What was the most important thing you
learned?
– What is one question you would still like
answered?