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A chemical reaction is the process of breaking
of chemical bonds (ionic or covalent) in one
or more substances, and the reforming of
new bonds to create new substances
indicators of chemical change are:
1.
formation of new gas
2.
formation of new precipitate (solid)
3.
release of energy (heat or light)
4.
color change
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energy is stored in the ionic and covalent
bonds of molecules
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exothermic reaction– energy is released
(burning)
endothermic reaction– energy is absorbed (cold
packs)
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some important chemical reactions
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burning of fossil fuels
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photosynthesis
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rusting of metals
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Conservation of mass
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matter cannot be created nor destroyed in
chemical reactions
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chemical equations convey as much info. as
possible about what happens in a chemical
reaction during a chemical change
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each side of the equation must have the same
number of atoms of each elements
bicycle example
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skeletal equation
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balanced equation
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frame + wheel + handlebar + pedal → bike
frame + 2 wheels + handlebar + 2 pedals → bike
tricycle example
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skeletal equation
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frame + wheels + handlebar + bell → tricycle
balanced equation
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frame + 3 wheels + handlebar + bell → tricycle
NOT BALANCED!
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this is NOT balanced
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?KCl + ? H2SO4  ? HCl + ? K2SO4
2KCl + H2SO4  2HCl + K2SO4
NaCl (aq) + AgNO3 (aq)  AgCl (s) + NaNO3 (aq)
balanced
Al(s) + O2(g)  Al2O3(s)
4Al(s) + 3O2(g)  2Al2O3(s)