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EdExcel GCSE Chemistry > Energy Changes - Topic 7 > Flashcards

Energy Changes - Topic 7 Flashcards

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1
Q

Which changes do changes in heat energy accompany?

A
  • Salt dissolving in water
  • Neutralisation reactions
  • Displacement reactions
  • Precipitation reactions
    • When these reaction take place in solution, temperature solution can be measured to reflect the heat changes
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2
Q

Exothermic reaction:

A
  • a reaction where heat energy is given out to the surroundings so the temperature of the surroundings increases
  • makes bonds
  • temperature increases as chemical energy → thermal/heat energy
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3
Q

Endothermic reaction:

A
  • a reaction where heat energy is taken in from the surroundings so the temperature of the surroundings decreases
  • breaks bonds
  • temperature decreases as thermal/heat energy → chemical energy
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4
Q

How do you know if the overall heat energy change for a reaction is exothermic?

A
  • E is needed to break bonds and E is released when bonds are formed
  • the overall heat energy change for a reaction is exothermic if more heat is released in forming bonds in the products than is required in breaking bonds in the reactants
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5
Q

How do you know if the overall heat energy change for a reaction is endothermic?

A
  • E is needed to break bonds and E is released when bonds are formed
  • the overall heat energy change for a reaction is endothermic if less heat energy is released in forming bonds in the products than is required in breaking bonds in the reactants
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6
Q

Activation Energy:

A
  • the minimum amount of energy that particles must have for a reaction to take place
  • it is the minimum amount of energy with which the particles need to collide with to make the collisions successful
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7
Q

What happens if particles do not reach the activation energy?

A

The particles may still collide, but they will simply just bounce of each other

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8
Q

Is the activation energy different for each experiment?

A

yes

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9
Q

What do all substances have?

A

all substances have chemical energy - a form of stored or potential energy

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10
Q

How does energy change in chemical reactions?

A

when chemical reactions occur and new substances are formed with different amounts of energy - energy can be exchanged with the surroundings and can be released or absorbed as heat

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11
Q

Enthalpy change:

A
  • The difference between the energy of the reactants and the energy of the products - approximately the amount of energy lost or gained during the reaction
  • ΔH (“delta H”)
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12
Q

What is the energy change for an exothermic reaction?

A
  • energy change is negative
  • as more heat energy has been released
  • negative ΔH
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13
Q

What is the energy change for an endothermic reaction?

A
  • energy change is positive
  • as heat energy has been absorbed/taken in
  • positive ΔH
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14
Q

How do you calculate the energy needed to break bonds and the energy released when bonds are formed?

A

the energy needed to break bonds and energy released when bonds are formed
can both be calculated from bond energies

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15
Q

How do you calculate the overall energy change for a reaction?

A

overall energy change = sum of energy taken in to break bonds – sum of energy released to form bonds

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16
Q

How can you tell from the energy change whether a reaction is exothermic or endothermic?

A
  • if the energy out > energy in, the energy change will be negative showing an exothermic reaction
  • if the energy out < energy in, the energy change will be positive showing an endothermic reaction
17
Q

Overall energy change of the reaction:

A

the difference between the sum of the energy needed to break bonds in the reactants and the sum of the energy released when bonds in the products are formed

18
Q

Reaction profile:

A
  • graphs used to show the relative energies of reactants and products
  • the activation energy and the overall energy change of a reaction
19
Q

Energy profile for exothermic reaction pathway:

A
20
Q

Energy profile for endothermic reaction pathway:

A
21
Q

Energy profile for reaction using catalyst:

A
22
Q

How do you compare the temperature changes of a neutralisation reaction when 2 different acids are used to neutralise an alkali solution?

A
  • measure known volume of alkali solution
  • add same volume of each of the acids
  • stir the mixture
  • record the initial and final temperatures/temperature change

EdExcel GCSE Chemistry (29 decks)

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