iiiiiiivv i.intro to reactions ch. 8 – chemical reactions
TRANSCRIPT
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I II III IV V
I. Intro to Reactions
Ch. 8 – Chemical Reactions
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A.Signs of a Chemical Reaction
Evolution of heat and light Formation of a gas Formation of a precipitate Color change
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B.Law of Conservation of Mass mass is neither created nor destroyed
in a chemical reaction
4 H
2 O
4 H
2 O4 g 32 g
36 g
total mass stays the same atoms can only rearrange
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C. Chemical Equations
A+B C+DREACTANTS PRODUCTS
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C. Chemical Equations
Pt a catalyst is present (in this case, platinum)
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D. Writing Equations
Identify the substances involved. Use symbols to show:
2H2(g) + O2(g) 2H2O(g)
How many? - coefficient
Of what? - chemical formula
In what state? - physical state Remember the diatomic elements.
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D. Writing Equations
Two atoms of aluminum react with three formula units of aqueous copper(II) chloride to produce three atoms of copper and two formula units of aqueous aluminum chloride.
• How many?• Of what?• In what state?
Al 2 (s) + 3CuCl2(aq) 3 Cu(s) + 2AlCl3(aq)
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E. Describing Equations
Describing Coefficients:
individual atom = “atom”
covalent substance = “molecule”
ionic substance = “formula unit”
3 molecules of carbon dioxide
2 atoms of magnesium
4 formula units of magnesium
oxide
3CO2
2Mg
4MgO
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Subscripts vs. Coefficients
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E. Describing Equations
to produce
• How many?• Of what?• In what state?
Zn(s) + 2HCl(aq) ZnCl2(aq) + H2(g)
One atom of solid zinc reacts withtwo molecules of aqueous hydrochloric acid one f.u.of aqueous zinc chloride and onemolecule of hydrogen gas.
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I II III IV V
II. Balancing Equations
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A. Balancing Steps1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Note: you may not change a subscript
Coefficient subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!
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B. Helpful Tips
Balance one element at a time. Update ALL atom counts after adding
a coefficient. If an element appears more than
once per side, balance it last. Balance polyatomic ions as single
units. “1 SO4” instead of “1 S” and “4 O”
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Al + CuCl2 Cu + AlCl3
Al
Cu
Cl
1 1
1 1
2 3
2
3
6
3
33 2
C. Balancing Example
Aluminum and copper(II) chloride react to form copper and aluminum chloride.
2
2
6
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Balancing Balancing EquationsEquationsBalancing Balancing EquationsEquations
____C____C33HH88(g) + _____ O(g) + _____ O22(g) ---->(g) ---->
_____CO_____CO22(g) + _____(g) + _____ H H22O(g)O(g)
________BB44HH1010(g(g) ) + _____ O+ _____ O22(g) ---->(g) ---->
___ B___ B22OO33(g) + _____ H(g) + _____ H22O(g)O(g)
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Balancing EquationsBalancing EquationsBalancing EquationsBalancing Equations
Sodium phosphate + iron (III) oxide Sodium phosphate + iron (III) oxide sodium oxide + iron (III) phosphatesodium oxide + iron (III) phosphate
NaNa33POPO44 + Fe + Fe22OO33 ----> ---->
NaNa22O + FePOO + FePO44