Transcript Classifying Chemical Reactions 9-3

Unit 4: Toxins
Intro Chemistry
Chemical Toxins
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Chemistry is the study of matter and the
changes that it undergoes.
We have learned about how chemical
compounds are formed
We have also learned the language of
chemistry, chemical formulas
Certain chemicals interact with the human
body in a negative way and are known as
toxins
Now we will equations for chemical
reactions to learn about toxic substances.
Keeping Track of Atoms
Law of Conservation of Matter
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Conservation of Matter: in all chemical
and physical changes, matter is neither
created or destroyed
• The total mass in a chemical reaction remains
constant
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Antoine Lavoisier:
• Made accurate and precise
measurements during chemical
reactions
• Found that the total mass at the
beginning = total mass at end of
reaction
Chemical Reactions
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A chemical change is really a chemical reaction
Has two parts:
• Reactants: the substances you start with
• Products: the substances you end up with
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The reactants turn into the products
4 Fe + 3 O2
 2 Fe2O3
Reactants  products
Ways to Express a Chemical
Reaction
The way atoms are joined is changed in a
chemical reaction.
Can be described several ways:
1. In a sentence
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Copper reacts with chlorine to form copper (II)
chloride.
2. In a word equation
Copper + chlorine  copper (II) chloride
3. In chemical formulas:
Cu + Cl2  CuCl2
Symbols in equations
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the arrow  separates the
reactants from the products
(s) or  after the formula = solid
(g) or after the formula = gas
(l) after the formula = liquid
(aq) after the formula - dissolved
in water, an aqueous solution
Symbols used in equations
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reaction
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indicates a reversible
shows
that heat is supplied to the
reaction
Pt
is used to indicate a
 
catalyst is supplied, in this case,
platinum.
heat
  ,   
What is a catalyst?
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A catalyst is a substance that
speeds up a reaction, without
being changed or used up by the
reaction.
Enzymes are biological or protein
catalysts.
Skeleton and Balanced
Equations
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Use formulas and symbols to describe a
reaction
Don’t indicate how many of each
element/compound
Balanced equations: the number of atoms
of each element is the same on both
sides of the reaction.
Use coefficients to balance equation
Coefficients and Subscripts
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Coefficients: large whole numbers placed
in front of formula which represents
number of units of that compound
Subscript: small whole number placed in
chemical formula to represent number of
atoms of an element in a compound
4 Fe + 3 O2
Coefficient
 2 Fe2O3
subscript
Study Buddy Review
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What is the Law of Conservation of
mass?
What does the symbol (l) mean?
What does (aq) mean?
What is a coefficient?
What is a subscript?
How to Balance
Chemical Equations
Balanced Equation
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A balanced equation has the
same number of atoms of each
element on both sides of the
equation
Atoms can’t be created or
destroyed
All the atoms at the beginning
must appear in the end
C
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+
O
O
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C
O
C + O2  CO
We need one more oxygen in the
products.
Can’t change the formula, because it
describes what it is (carbon
monoxide in this example)
C
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+
O
O
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C
O
C
O
Must be used to make another
CO
But where did the other C come
from?
C
+
C
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O
O
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C
O
C
O
Must have started with two C
2 C + O2  2 CO
Rules for balancing:
 Assemble, write the correct formulas for
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all the reactants and products
Count the number of atoms of each type
of element appearing on both sides
Balance the atoms of an element one at a
time by adding coefficients (the numbers
in front) - save H and O until LAST!
Check to make sure it is balanced.
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Never change a subscript to balance an
equation.
• If you change the formula you are
describing a different reaction.
• H2O is a different compound than H2O2
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Never put a coefficient in the middle of
a formula
• 2 NaCl is okay, Na2Cl is not.
Balancing Equations Examples
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H2 (g) + O2 (g) 
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Zn +
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Pb (NO3)2 +
HCl
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H2O (l)
H2 +
K2S 
ZnCl2
PbS + KNO3