energy changes Flashcards

1
Q

what is an exothermic reaction

A
  • when a gas is released during a reaction
  • heat energy is released into the environment
  • the internal temp of the reaction is decreasing while the external is increasing due to release of thermal energy
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2
Q

what is an endothermic reaction

A
  • heat is absorbed from environment into the reaction
  • the internal temp of the reaction is increasing whilst the external temp is decreasing due to the absorption of thermal energy
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3
Q

examples of exothermic reactions

A
  • chemical hand and body warmers
  • self heating cans
  • combustion
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4
Q

examples of endothermic reactions

A
  • cold packs
  • melting
  • photosynthesis
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5
Q

how do cold packs work

A
  • most cold packs contain ammonium nitrate or water
  • ammonium nitrate dissolves and absorbs energy from surrounding making them colder
  • only work for about 20 mins and not reusable
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6
Q

how do hot packs work

A
  • crystallisation of a supersaturated solution is used in reusable warmers
  • single use warmers tend to last for longer
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7
Q

what are reaction profiles

A

they show the relative amounts of energy contained in the reactants and reactants

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8
Q

reaction profile - exothermic

A

reactants line is higher than the products line

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9
Q

reaction profile - endothermic

A

reactants line is lower than the products line

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10
Q

what is the activation energy

A

the minimum amount of energy needed to cause/ start a reaction

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11
Q

how is activation energy shown in a reaction profile

A

arrow starting at reactants line and ending at the peak (pointing upwards)

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12
Q

bond breaking and making

A
  • chemical bonds are broken when energy is absorbed (endothermic)
  • chemical bonds are made/ formed when energy is released (exothermic)
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13
Q

what is bond energy

A

the energy needed to break bonds between atoms

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14
Q

bond energy calculations

A

list of bond energy for individual bonds are given, add to find total

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