IIIIIIIVV Intro to Reactions Chemical Reactions. Signs of a Chemical Reaction n Evolution of heat...
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Transcript of IIIIIIIVV Intro to Reactions Chemical Reactions. Signs of a Chemical Reaction n Evolution of heat...
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I II III IV V
Intro to Reactions
Chemical Reactions
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Signs of a Chemical Reaction
Evolution of heat and light Formation of a gas Formation of a precipitate (solid) Color change
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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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Chemical Equations
A+B C+DREACTANTS PRODUCTS
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Chemical Equations
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Subscripts
Subscripts are the numbers proceeding an element.
The number represents how many atoms are present of that specific element.
Examples: H2O = 2H, 1O
AgNO3 = 1Ag, 1N, 3O
Mg(NO3)2 = 1Mg, 2N, 6O
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Coefficients
Coefficient – is the number in front of an element or compound.
The number represents how many of that specific compound is present.
Examples: 2H2O = 4H, 2O 3CO = 3C, 3O 2Mg(NO3)2= 2 Mg, 4N,12O
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Writing Equations
Identify the substances involved. Use symbols to show:
2H2(g) + O2(g) 2H2O(g)
How many? – coefficient & subscript
Of what? - chemical formula
In what state? - physical state
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Writing Equations
Two atoms of aluminum react with three units of aqueous copper(II) chloride to produce three atoms of copper and two 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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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 unitof aqueous zinc chloride and onemolecule of hydrogen gas.
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Balancing Steps
1. Write the unbalanced equation.
2. Count atoms on each side.
3. Add coefficients to make #s equal.
Coefficient subscript = # of atoms
4. Reduce coefficients to lowest possible ratio, if necessary.
5. Double check atom balance!!!
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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
Balancing Example
Aluminum and copper(II) chloride react to form copper and aluminum chloride.
2
2
6