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AQA GCSE Chemistry > 5. Energy Changes > Flashcards

5. Energy Changes Flashcards

1
Q

What is an exothermic reaction?

A

One that gives out energy to the surroundings

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2
Q

What is an endothermic reaction?

A

One that takes in energy from the surroundings

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3
Q

In terms of energy, what happens when bonds are broken?

A

Energy is required (endothermic)

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4
Q

In terms of energy, what happens when bonds are formed?

A

Energy is released (exothermic)

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5
Q

How do you remember whether energy is released or required when bonds are being rearranged?

A

Bendy Mexicans

B(endo)ROKEN
M(exo)ADE

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6
Q

What does it mean if the energy of the products is lower than the reactants?

A

Energy has been released and the reaction is exothermic

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7
Q

What does it mean if the energy of the products is higher than the reactants?

A

Energy has been taken in and the reaction is endothermic

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8
Q

How does a catalyst increase the rate of reaction?

A

By lowering the activation energy

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9
Q

How do you work out total energy change?

A
  • total for breaking bonds: no. of bonds x energy it takes to break that type of bond
  • total for making bonds: no. of bonds x energy it takes to make that type of bond
  • total energy change: breaking bonds - making bonds
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10
Q

What does it mean if you get a positive number when working out energy change?

A

The reaction is endothermic

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11
Q

What does it mean if you get a negative number when working out energy change?

A

The reaction is exothermic

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12
Q

In terms of energy change, what do exothermic and endothermic reactions always have?

A
  • endothermic always have positive energy changes

* exothermic always have negative

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13
Q

How can a simple cell be made?

A

By connecting two different metals in contact with an electrolyte

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14
Q

What do batteries consist of to provide a greater voltage?

A

Two or more cells connected

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15
Q

What chemicals are cells made from?

A
  • carbon rod with metal cathode
  • manganese oxide
  • ammonium chloride
  • zinc casting anode
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16
Q

What is the electrolyte in a cell made of?

A

Ammonium chloride

17
Q

What is the anode made of in a cell?

A

Zinc casting

18
Q

What does the voltage produced by a cell depend on?

A

The type of metals making up the cathode and anode and electrolyte

19
Q

What happens when two metals are dipped in salt solution and joined by a wire?

A

The more reactive metal will donate electrons to the less reactive metal to form an electrical cell

20
Q

Which metal will lose their electrons in a simple electrical cell?

A

The more reactive metal

21
Q

What happens when there is a greater difference between reactivity of metals in a cell?

A

There will be a higher voltage produced

22
Q

Are alkaline batteries rechargeable?

A

No

23
Q

What happens when one of the reactants has been used up in non-rechargeable batteries?

A

The chemical reactions stop

24
Q

What happens to the chemical reactions in rechargeable batteries?

A

They are reversed using an external electrical current

25
Q

How do hydrogen fuel cells work?

A
  • oxygen is supplied to the positive electrode and diffuses through the graphite to react to form hydroxide ions - accepting electrons from the external circuit
  • hydrogen is supplied to the negative electrode and diffuses through the graphite electrode and reacts with hydroxide ions to form water
  • overall charge left in fuel cell
26
Q

What hydrogen fuel cells offer an alternative to?

A

Fossil fuels and rechargeable cells and batteries

27
Q

Advantages of hydrogen fuel cells?

A
  • don’t need to be electrically recharged
  • no pollutants produced
  • can be a range of sizes for different uses
  • do not get less efficient as they run
  • can be a source of drinking water
28
Q

Disadvantages of hydrogen fuel cells?

A
  • hydrogen is flammable and difficult to store
  • hydrogen is sometimes produced for the cell by non renewable sources
  • produce a relatively low voltage so several are needed together
29
Q

What are fuel cells useful as an energy source for aircraft?

A
  • provide water
  • efficient
  • no moving parts
  • lightweight
30
Q

What are the main disadvantages of using hydrogen fuel cells for aircraft?

A
  • have poisonous catalysts

* producing the hydrogen and oxygen will use energy elsewhere

31
Q

Half equation for the hydrogen supplied to a hydrogen fuel cell? (anode)

A

H2 -> 2H+ + 2e-

32
Q

Half equation for the oxygen supplied to a hydrogen fuel cell?

A

02 + 4H+ + 4e- -> 2H2O

33
Q

Equation for the two electrode reactions in a hydrogen fuel cell?

A

2H2 + O2 -> 2H2O

AQA GCSE Chemistry (10 decks)

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