Moles and Chemical Reactions

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Moles and Chemical Reactions

• Chapter 9, sections 9.1 and 9.2

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Relationships in Reactions

• Lets say you are making a cake and you need 1 cup
  baking mix, 1 egg and 1 cup water per serving.
• 1 c. baking mix 1 egg 1 c. water 1 serving
  of cake
• Lets say I need 30 servings. How many cups of
  baking mix, how many eggs, and how many cups of
  water would I need?
• 30 c. baking mix 30 eggs 30 c. water 30
  servings of cake

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Relationships in Reactions cont

• You can do this with a lot of things. Let say I
  need 1 yard of fabric, 3 yards of thread and 4
  buttons to make 1 skirt
• 1 yard of fabric 3 yards of thread 4 buttons
  1 skirt
• So my friends think this skirt is pretty cool and
  ask me to make 8 more. How much of the materials
  would I need?
• 8 yards of fabric 24 yards of thread 32
  buttons 8 skirts
• So what this can also be saying is that I have a
  134 ratio per skirt and I can multiply it by
  the number of skirts I need!
• What would be my ratio if I need 12 skirts
• 123648? 12 skirts

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Relationships in Reactions cont

• The same concept works in chemistry!!!
• Lets say I have the equation
• K Cl2 ? KCl
• Balance the equation
• So what can this mean?
• 2 atoms of K 1 molecule of Cl2? 2 molecules of
  KCl
• It is also a ratio!!!

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Relationships in Reactions cont

• Lets try another!
• CO (g) H2 (g) ? CH3OH (l)
• Balance the reaction
• I could multiply this by any number and still be
  balance (although not in the lowest integers)
• So I multiplies this by 10, I could get
• 10 CO (g) 20 H2 (g) ? 10 CH3OH (l)

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Relationships in Reactions cont

• Okay, so if we have
• CO (g) 2H2 (g) ? CH3OH (l)
• It would be the same as this
• 5CO (g) 10H2 (g) ? 5CH3OH (l)
• Or
• 2CO (g) 4H2 (g) ? 2CH3OH (l)
• Or
• 2CO (g) 2H2 (g) ? CH3OH (l)

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Relationships in Reactions cont

• I could also multiply it by a huge number like
• 6.022 x1023 ?
• 6.022 x1023 CO (g) 1.204 x1024 H2 (g) ? 6.022
  x1023 CH3OH (l)
• Or could say
• 1 mole CO (g) 2 moles H2 (g) ? 1 mole of CH3OH
  (l)

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Relationships in Reactions cont

• Example
• Look at the following equation. Give a balanced
  reaction and state the meaning of the equation in
  terms of molecules and moles.
• NO (g) O2 (g) ? NO2 (g)
• 2 molecules of nitrogen monoxide gas combine 1
  molecule of oxygen gas to form 2 molecules of
  nitrogen dioxide
• 2 moles of nitrogen monoxide gas combine 1 mole
  of oxygen gas to form 2 moles of nitrogen dioxide

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Mole to Mole relationships

• We can use this idea of ratios to determine the
  number of moles used and produced in chemical
  reactions!
• Say I have the reaction
• C (s) O2 (g) ? CO2 (g)
• This means I can have 1 mole of C combining with
  1 mole of O2 to form 1 mole of carbon dioxide
• What would happen if I had 2 moles of each?
• 2C (s) 2 O2 (g) ? 2CO2 (g)
• Then have 2 moles of C combining with 2 moles of
  O2 to form 2 moles of carbon dioxide
• What would happen if I had .25 moles of each?
• .25 moles C (s) .25 moles O2 (g) ? .25 moles
  CO2 (g)

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Mole to Mole relationships

• Lets try another!
• 2H2O ? 2H2 O2
• 2 moles of water decompose to form 2 moles of H2
  and 1 mole of O2
• Let suppose there are 4 moles of H2O
• 4H2O ? 4H2 2O2
• How about 5.8 moles of H2O
• 5.8 H2O ? 5.8 H2 2.9 O2
• Why 2.9 of O2?
• Because there were only ½ the amount of oxygen as
  there were of water

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Mole to Mole relationships

• These are called MOLE RATIOS
• Mole ratio The ratio of moles of one substance
  to moles of another substance in a chemical
  reaction
• Example
• How many moles of each would I have if I had .25
  moles of the first species
• H2S Ag ? Ag2S H2
• So that would mean
• .25 moles H2S .50 moles Ag ? .25 moles Ag2S
  .25 moles H2

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Homework

• Read pages 251-258. Problems 1,2,5 on page
  258. Problems 4 and 8 on page 282