C7 : Energy changes Flashcards

1
Q

What is an exothermic reaction?

A

A reaction that TRANSFERS energy into the surroundings.

  • makes surroundings WARMER
  • products have less chemical energy than reactants (reaction gets colder)
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2
Q

Uses of exothermic reactions. (3)

A

HAND WARMERS- USED ONCE
- oxidation of IRON releases energy. Iron turns to hydrated iron oxide in exothermic reactions.
REUSABLE HANDWARMERS
- when metal disc is pressed, small particles of metal scraped off.
- this starts CRYSTALLISATION and spreads in solution starts an exothermic change
SELF HEATING CANS
- Calcium oxide + water –> calcium hydroxide transfers energy to food/drink
- pressing button on can, breaks a seal and lets calcium oxide + water mix - start exothermic reaction

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3
Q

What is an endothermic reaction?

A

A reaction that transfers energy FROM the surrounding TO the reacting chemicals.

  • TEMPERATURE OF SURROUNDINGS ALWAYS GOES DOWN
  • products have MORE chemical energy than reactants
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4
Q

Uses of endothermic reactions.

A

COLD PACKS

  • contain ammonium nitrate + water
  • when ammonium nitrate dissolves in water, it absorbs energy from surroundings, making them colder
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5
Q

What is the reaction when more energy is needed to break bonds than make bonds?

A

Endothermic (energy is needed to break bonds)

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6
Q

What is the reaction where more energy is used to form bonds than break them?

A

Exothermic

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7
Q

Explain, using ideas about particles and atoms, why burning magnesium is an exothermic change.

A
  • After the collisions of particles during a chemical reaction, energy is taken in to break the reactant bonds and then when bonds form, energy is released.
  • Burning magnesium is an exothermic reaction because more energy is released to the surroundings in the process of bond-making, than absorbed from the surroundings in the process of bond-breaking.
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8
Q

Energy change equation

A

energy change = break - make

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9
Q

How can you tell if a reaction is endo or exo?

A

If the energy of products is HIGHER than of the reactants it is ENDOTHERMIC.
If the energy of products is LOWER than the reactants it is EXOTHERMIC.

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10
Q

What measurements would a student make to show that the reaction is exothermic?

A

The temperature before and after.

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