IIIIIIIVV I.Intro to Reactions Ch. 8 – Chemical Reactions.
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Transcript of IIIIIIIVV I.Intro to Reactions Ch. 8 – Chemical Reactions.
I II III IV V
I. Intro to Reactions
Ch. 8 – Chemical Reactions
A.Signs of a Chemical Reaction
Evolution of heat and light Formation of a gas Formation of a precipitate Color change
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
C. Chemical Equations
A+B C+DREACTANTS PRODUCTS
C. Chemical Equations
Pt a catalyst is present (in this case, platinum)
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.
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)
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
Subscripts vs. Coefficients
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.
I II III IV V
II. Balancing Equations
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!!!
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”
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
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)
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