Endo

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Endo Exothermic Rxns

• Agenda
• Quick Quiz
• Notes on endo vs. exo
• PE diagrams
• 12-1 Apply for homework.

2
Quick Quiz

• If the temperature of the sand rises 10oC, the
  mass of the sand is 1000 g and it absorbed 1000
  calories, what is the specific heat of the sand?

3

• What is heat energy?
• What does it do to atoms?

4

• What does the word exit mean?
• Is getting kicked out of class a positive or
  negative experience?

5

• What does the prefix endo mean?

6

• Thermasilk is a brand-name shampoo. What does
  the prefix therm mean?

7

• If a reaction is exothermic, what do you think
  is happening?

8

• What happens when atoms break their bonds with
  other atoms?
• With fireworks, which side of the reaction is the
  heat energy?

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Endo Exothermic Reactions

• Date

10
System

• The part of the universe on which you focus your
  attention.
• Test tube, beaker, classroom

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Surroundings

• Everything outside of the system.
• Classroom, school, world

12
Universe

• The system and surroundings together.

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Endothermic

• Process that absorbs heat from the surroundings
• Feels cold because your hand (body) is part of
  the surroundings.
• Temperature will go down.
• Heat, q is positive
• Chemical potential energy of reactants is lower
  than the products.

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Activation Energy

• The energy required to get reaction going.
• Striking a match
• In order for a reaction to occur, the substances
  must collide with the proper orientation and set
  energy.

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Catalyst

• A species that speeds up the rate of reaction
  without itself being consumed.
• Lowers the activation energy required to get the
  reaction going.

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Potential energy diagram for endothermic reactions
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Exothermic Reactions

• Process in which energy is released to the
  surroundings.
• Feels hot because your hand (body) is part of the
  surroundings.
• The temperature goes up.
• Heat, q is negative
• Chemical potential energy of reactants is higher
  than the products.

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Potential energy diagram for exothermic reactions
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Calorimeter

• A device used to measure the amount of heat
  absorbed or released during a physical or
  chemical process.
• Good calorimeters do not absorb much heat allow
  all to be transferred to water.

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Relating endo and exo

• Endothermic - Exothermic
• Allows us to use data from calorimeter to
  determine specific heat or heat of reaction.
• Next lab, heat up metal and put into calorimeter.

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Enthalpy

• The amount of heat a substance has at a given
  temperature and pressure.
• The enthalpy change, DH is the heat change for a
  process at constant pressure
• Difference between potential energies of
  reactants and products.
• If DH is negative, the rxn is exothermic
• If DH is positive, the rxn is endothermic.