Chemical Reactions Review

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Chemical Reactions Review
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How can you tell if there was a chemical reaction?

• Chemical reaction Chemical change
• Heat change
• Absorbed or produced
• http//jchemed.chem.wisc.edu/JCESoft/CCA/CCA0/Movi
  es/NACL1.html
• Visible clues
• Color change
• http//jchemed.chem.wisc.edu/JCESoft/CCA/CCA0/MOVI
  ES/NI3IOD.html
• Solid forms from a liquid http//jchemed.chem.wisc
  .edu/JCESoft/CCA/CCA0/MOVIES/AGNONAOH.html
• Flame
• Bubbles (gas)

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Chemical equations

• Chemical Reaction
• A process by which the physical and chemical
  properties of the original substances change into
  new substances with different physical and
  chemical properties
• Reactants
• The stuff on the left side of the arrow.
• The original substances
• Products
• The stuff on the right side of the arrow.
• The new substances

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Chemical equations cont

• Chemical Equations A written way to express a
  chemical reaction.
• Example
• Mg O2 ? MgO
• Magnesium Oxygen yields Magnesium oxide
• This is not balanced yet
• http//jchemed.chem.wisc.edu/JCESoft/CCA/CCA3/STHT
  M/MAGAIR/MAGAIR.HTM

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Chemical equations cont

• Law of the conservation of mass
• Matter can be neither created or destroyed
• The number of atoms on both sides of a chemical
  reaction remains the same
• SO WE HAVE TO BALANCE EQUATIONS!!!

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Chemical equations cont

• Chemical balancing RULES!!!
• Read the description of the chemical reaction,
  write down the formulas of the reactants and the
  products (and their states, but that will be
  discussed later)
• Write the unbalanced reaction that summarizes the
  change
• Balance the equation by inspection. You CANNOT
  change the chemical formulas, but you can change
  the coefficients (the number in front, or how
  many atoms or molecules that are in the reaction)
• Check to see if all the types of atoms on one
  side of the arrow match the same type on the
  other, and that the coefficients are in the
  lowest integers possible

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Chemical equations cont

• Mg O2 ? MgO
• There are 2 oxygens on the left and only 1 on the
  right.
• So you need to make 2 on each side
• I can only use a coefficient and I have to put it
  in front on the whole molecule
• Now I have only 1 Mg on the left side and 2 on
  the right
• Now I have 2 Mg on both sides and 2 O on both
  sides, it is balanced

2
2
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Chemical equations cont
2
2
3
4

• Fe O2 ? Fe2O3
• So lets try one!
• How many irons do we have on the reactants side?
  The products side?
• What do we have to do to balance the irons?
• So the irons are balanced, now what about the
  oxygens?
• What do we need to do to balance the oxygens?
• Uh-oh- I guess we have to change both the
  products and reactants
• Well poop! Now we have to change the iron again!
• Yea! It is balanced!

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Chemical equations cont

• We also can indicate the state of the matter in a
  reaction
• (s) solid
• (l) liquid
• (g) gas
• (aq) dissolved in water- (aqueous)
• K(s) H2O(l) ? H2 (g) KOH (aq)
• 2K(s) 2H2O ? H2(g) 2KOH(aq)

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Homework

• Read pages 193-207, problems 1-5 on page 207