Energy Change Flashcards

1
Q

Exothermic reaction

A

One which gives out heat to the surroundings. The energy released is grater than energy used in breaking old bonds.

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2
Q

Endothermic reaction

A

One which takes in energy from the surroundings. The energy required to break old bonds is greater than the energy released when new bonds are formed.

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3
Q

Energy in chemical reactions

A

Energy is transferred in chemical reactions because old bonds are broken and new bonds are formed.

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4
Q

Endothermic process

A

Energy must be supplied to break existing bonds.

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5
Q

Exothermic process

A

Energy is released when new bonds are formed.

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6
Q

Bond dissociation energy

A

The energy needed to break the bond between two atoms. Every chemical bond has particular bond energy.

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7
Q

Formula of energy change

A

Energy change=energy of bond breaking - energy of bond making

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8
Q

Energy change negative

A

Means that more energy was released in bond making so the reaction is exothermic.

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9
Q

Energy change positive

A

Means that more more energy was used in bond breaking than was released by bond making do the reaction is endothermic.

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10
Q

Energy level diagram

A

Shows how the energy in a reaction changes as the reaction progresses.

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11
Q

Catalyst

A

Is a substance that can speed up a chemical reaction without being changed or used up during the reaction.

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12
Q

Endothermic energy level diagram

A

Reactants are at lower energy than the products.

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13
Q

Exothermic energy level diagram

A

Reactants are at a higher energy than the products.

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14
Q

Energy transferred formula

A

Q = m x c x deltaT

Energy transferred = mass(g) x specific heat capacity x temperature change

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15
Q

Example of an endothermic reaction

A
  • sport injury packs are based on it

- thermal decomposition (it will only break down if it is heated enough)

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16
Q

Examples of exothermic reaction

A
  • fuel combustion
  • self-heating coffee
  • hand warmer
17
Q

Disposable hand warmer

A
  • The energy released through oxidation of iron
  • iron turns into hydrated iron (lll) oxide, similar to rusting
  • sodium oxide is used as a catalyst
18
Q

How does sports injury pack work?

A

When ammonium nitrate and water inside the pack mixes, causing an endothermic reaction.

19
Q

Thermal decomposition example

A

Decomposition of calcium carbonate. This forms calcium oxide and carbon dioxide when we keep heating the calcium carbonate strongly.

20
Q

How does catalyst work?

A

Catalyst provides different pathway so the activation energy is lower. This means that a higher proportion of reactant particles now have enough energy to react when they collide.

21
Q

ΔH

A

Enthalpy energy