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(c) McGraw Hill Ryerson 2007
• Chemical reactions result in chemical changes.– Chemical changes occur when new substances
are created.– The original substance(s), called reactants,
change into new substance(s) called products.
See pages 202 - 203
(c) McGraw Hill Ryerson 2007 See pages 202 - 203
(c) McGraw Hill Ryerson 2007
• Chemical reactions can be written in different ways.
– A word equation:• Nitrogen monoxide + oxygen nitrogen dioxide
– A symbolic equation:• 22NO(gg) + O2(gg) 22NO2(gg)
STATE OF MATTERSTATE OF MATTER
- Letters indicate the state of each compound.
(aq) = aqueous/dissolved in water
(s) = solid
( ) = liquid
(g) = gas
COEFFICIENTSCOEFFICIENTS
- Indicates how many of each molecule there is.
-Ie: there are 2 molecules of NO.
(c) McGraw Hill Ryerson 2007
• When a chemical reaction occurs, new compounds are created, BUT…– No new matter is created or destroyedNo new matter is created or destroyed; atoms are
just rearrangedrearranged as the atoms change partners change partners to form new compounds.
– If there are 3 atoms of oxygen in the reactants, there MUST be 33 atoms of oxygen in the products.
– Number of each atom in reactants = number of each Number of each atom in reactants = number of each atom in products.atom in products.
• The law of conservation of mass:– Mass of reactants = mass of products
If you could collect and measure all of the exhaust from this car, you would find that mass of reactants (gas + O2) = mass of products (exhaust).
• A balanced chemical equation balanced chemical equation shows all atoms and the coefficientscoefficients tells us how many molecules (and atoms) there are.– Balancing ensures ensures that the number of each number of each
atom atom is the same on both sides same on both sides of the reaction arrow.
44K + O2 22K2O
K
K
K
K
K
K
K
K
O O O
O
(c) McGraw Hill Ryerson 2007
Skeleton equation: CH4 + O2 H2O + CO2
Carbon = 11 Carbon = 11
Hydrogen = 44 Hydrogen = 22
Oxygen = 22 Oxygen = 33
Balanced equation: CH4 + 22O2 22H2O + CO2 Carbon = 11 Carbon = 11
Hydrogen = 44 Hydrogen = 44
Oxygen = 44 Oxygen = 44
The same number of atoms must be on
each side.
See Page 207
Balancing Equations
ReactantsReactants ProductsProducts
HH 22 22
hydrogen + oxygen water
OO22 HH22OOHH2 2 ++
OO 22 11
Balancing Equations
H2 + O2 H2O2
ReactantsReactants ProductsProducts
HH 22 22
OO 22 22
hydrogen + oxygen hydrogen peroxide
XYOU CANNOT CHANGE THE SUBSCRIPTS
Balancing Equations
H2 + O2 H2O
ReactantsReactants ProductsProducts
HH 22 22
OO 22 11
hydrogen + oxygen water
22
Balancing Equations
H2 + O2 H2O
ReactantsReactants ProductsProducts
HH 22 44
OO 22 22
hydrogen + oxygen water
22
Balancing Equations
22 H2 + O2 H2O
ReactantsReactants ProductsProducts
HH 44 44
OO 22 22
hydrogen + oxygen water
22(g) (g) (l)
http://www.authorstream.com/Presentation/kellymdeters-86103-section-2-7-balancing-chemical-equations-education-ppt-powerpoint/
• Balance the following:– ____Fe + ____Br2 _____FeBr3
Sn(NO2)4 + K3PO4 KNO2 + Sn3 (PO4)4
C2H6 + O2 CO2 + H2O
____Ba + ____H2O ____Ba(OH)2 + ____H2
____CO2 + ____H2O ____H2CO3
____Fe2O3 + ____C ____Fe + ____CO
____Fe + ____H2O ____H2 + ____Fe2O3
