CHEMICAL REACTIONS

1
CHEMICAL REACTIONS

•  
• L.H.S. R.H.S.
• Reactants Products
• FROM LAW OF CONSERVATION OF MASS
• Must have Same Number of Atoms of Each Type on
  Both Sides of the Equation
•  

2
SIMPLE COMBUSTION REACTION

• ExampleBURN PROPANE IN AIR (Gas Grill)
•  
• Propane Oxygen ?Carbon Dioxide Water
•  
• C 5 H 12 (g) O 2 (g) ? CO 2 (g) H 2O
  (l)
•  

3
PHASES OF REACTANTS PRODUCTS

• NOTE Indicate physical state of each species
  by (phase)
•  
• e.g. (g) gas
• (s) solid
• (l)   liquid
• (aq.) aqueous solution

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BALANCING CHEMICAL EQUATIONS

• Simple Approach
• 1. ASSIGN COEFFICIENT OF 1 TO MOST COMPLEX
  COMPOUND
• 2. LOOK FOR ELEMENTS THAT APPEAR ONLY ONCE IN
  EQN., AND TRY COEFFICENTS
• C5 H12 (g) O 2 (g) ?CO 2 (g) H 2O (l)

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BALANCE C

• (c) Balance C  
• C5 H12 (g) O2 (g) ? 5 CO2 (g) H2O(l)  

6
BALANCE H

• (b) Balance H
•  
• C5H12 (g) O2 (g) ? CO 2 (g) 6 H2O (l)

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BALANCE O

• (c) Balance O
•  
• (i) ADD UP O ON RHS 5 x 2 6 x 1 16
• (ii) O APPEARS AS O2 ON LHS ? NEED 16/2 x O2
• 1C5H12 (g) 16/2 O2 (g)? 5 CO2 (g) 6 H2O(l)

8
FINAL POLISHING

• CONVERT TO WHOLE NUMBERS
•   1C5H12 (g)8O 2 (g)?5CO2 (g)6H2O(l)

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CHECK COEFFICIENTS

• LHS RHS
• (1 x 5 C) 5 C 5 C
• (1 x 12 H) 12 H (6 x 2 H) 12 H
• (8 x 2 O) 16 O (5 x 2 O 6 x 1 O) 16 O

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BUT WHAT DOES THIS EQUATION MEAN?

• 1 C5 H12 (g) 8 O2 (g) ? 5 CO2 (g) 6 H 2O(l)
• 1.  1 MOLE of Propane Reacts with 8 MOLES of
  Oxygen to produce 5 MOLES of Carbon Dioxide 6
  MOLES of Water
• OR
• 2.   1 MOLECULE of Propane Reacts with 8
  MOLECULES of Oxygen to produce 5 MOLECULES
  of Carbon Dioxide 6 MOLECULES of
  Water