Lecture2'15: Endothermic

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Lecture-2.15 Endothermic Exothermic Reactions
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Endothermic Exothermic Reactions

• As all chemical reactions occur, there is also a
  heat change that occurs.
• The reactants for some chemical reactions absorb
  and store heat as they change into products.
• These reactions are called endothermic reactions.
• The reactants for some chemical reactions release
  heat as they change into products.
• These reactions are called exothermic reactions.

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Endothermic Exothermic Reactions

• Since endothermic reactions absorb and store
  heat, then a decreasing temperature is an
  indication of an endothermic reaction.

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Endothermic Exothermic Reactions

• Since exothermic reactions release heat, then an
  increasing temperature is an indication of an
  exothermic reaction.

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Endothermic Exothermic Reactions

• If a reaction is endothermic, then its reverse
  reaction will be exothermic and vice versa.
• Heat change can be measured by using a
  calorimeter.

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Endothermic Exothermic Reactions

• An endothermic reaction would absorb heat from
  the water and the waters temperature would
  decrease.

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Endothermic Exothermic Reactions

• An exothermic reaction would release heat to the
  water and the waters temperature would increase.
  

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Endothermic Exothermic Reactions

• The chemical reaction 2 C H2 ? C2H2 is
  endothermic.
• Endothermic reactions can be indicated two
  different ways.
• 2 C H2 ? C2H2 ?H 54 kcal
• when the heat is written off-to-the-side, the
  positive sign indicates an endothermic reaction.
• 2 C H2 54 kcal ? C2H2
• when the heat is written in-the-reaction, the
  heat on the left side indicates an endothermic
  reaction.

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Endothermic Exothermic Reactions

• The chemical reaction 4 Al 3 O2 ? 2 Al2O3 is
  exothermic.
• Exothermic reactions can be indicated two
  different ways.
• 4 Al 3 O2 ? 2 Al2O3 ?H ?798 kcal
• when the heat is written off-to-the-side, the
  negative sign indicates an exothermic reaction.
• 4 Al 3 O2 ? 2 Al2O3 798 kcal
• when the heat is written in-the-reaction, the
  heat on the right side indicates an exothermic
  reaction. notice no negative sign

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Endothermic Exothermic Reactions

• The endothermic reaction...
• 2 C H2 ? C2H2
• and the exothermic reaction...
• 4 Al 3 O2 ? 2 Al2O3
• are both synthesis reactions.
• Synthesis, decomposition, single replacement, and
  double replacement reactions can either be
  endothermic or exothermic.

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Endothermic Exothermic Reactions

• Combustion reactions are always exothermic.

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Endothermic Exothermic Reactions

• Ex.1) Is the reaction N2 3 H2 ? 2 NH3 22
  kcal endo or exothermic? _______________
• Ex.2) Is the reaction C O2 ? CO2 ?H ?94
  kcal endo or exothermic? _______________
• Ex.3) If you were to hold a beaker in which an
  endothermic reaction was taking place, would it
  feel hot or cold? ________
• Ex.4) Write the reaction N2 O2 44 kcal ? 2
  NO putting the heat off-to-the-side.
• ___________________________________

exothermic
exothermic
cold
N2 O2 ? 2 NO ?H 44 kcal
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Endothermic Exothermic Reactions

• Ex.5) Is the reaction 2 H2O 137 kcal ? 2 H2
  O2 endo or exothermic? _______________
• Ex.6) If you were to place a thermometer into a
  beaker in which an exothermic reaction was
  taking place, would the temperature increase or
  decrease? __________
• Ex.7) Write the reaction
• CH4 2 O2 ? CO2 2 H2O ?H ?213 kcal
• putting the heat into-the-reaction.
• ___________________________________

endothermic
increase
CH4 2 O2 ? CO2 2 H2O 213 kcal
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Endothermic Exothermic Reactions

• Ex.8) Is the reaction H2 I2 ? 2 HI ?H 13
  kcal endo or exothermic? _______________
• Ex.9) The instrument use to measure the heat
  absorbed or released in a reaction is called
  a(n) ____________.
• Ex.10) Write the reaction
• 2 C 3 H2 ? C2H6 20 kcal
• putting the heat off-to-the-side.
• ___________________________________

endothermic
calorimeter
2 C 3 H2 ? C2H6 ?H ? 20 kcal
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Endothermic Exothermic Reactions

• Ex.11) Combustion reactions will always be
  _____thermic.
• Ex.12) Reactions that absorb and store heat
  are called _____________ reactions.
• Ex.13) Melting is a NOT a chemical reaction but
  it is a physical reaction because no new
  substance is produced. When ice melts, is
  heat absorbed or released by the ice?
  __________
• Ex.14) Melting is an _____thermic reaction.

exo
endothermic
absorbed
endo
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Endothermic Exothermic Reactions

• Ex.15) A chemical cold pack is activated by
  squeezing the pack which breaks open a
  capsule allowing reactants to mix.
• Is the reaction in a chemical cold pack
  endo or exothermic? _____thermic.

endo
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Endothermic Exothermic Reactions

• Ex.16) A chemical hot pack is activated by
  squeezing the pack which breaks open a
  capsule allowing reactants to mix.
• Is the reaction in a chemical hot pack
  endo or exothermic? _____thermic.

exo