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GCSE AQA Chemistry > C7 > Flashcards

C7 Flashcards

1
Q

Exothermic and endothermic reactions in terms of bonds?

A

Breaking bonds aBsorbs energy, forRming bonds Releases energy

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2
Q

What is Activation energy?

A

minimum energy required for a reaction to take place

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3
Q

What kind of reactions are neutralisation reactions?

A

exothermic

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4
Q

RQ. What equipment do you need to investigate temperature changes?

A

poly(styrene) cup and thermometer

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5
Q

RQ. Method for investigating temperature changes? safety?
improvements?

A

• Record initial temperatures of reactants
• mix reactants in cup
• record max/minimum temperatures reached
• Safety = goggles
• improvements= lid for cup, stirring to get even distribution of heat

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6
Q

Uses of exothermic reactions? (2)

A

Chemical hand warmers, self-heating cans

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7
Q

3 main endothermic reactions?

A

Photosynthesis, hydrogen carbonate + acid (sherbet), dissolving ammonium nitrate in water

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8
Q

Equation for reaction in self-heating cans?

A

calcium oxide + water > calcium hydroxide

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9
Q

Uses of endothermic reactions?

A

Chemical cold packs

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10
Q

How do chemical cold packs work?

A

They contain ammonium nitrate and water, when ammonium nitrate dissolves, it absorbs energy from surroundings

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11
Q

What is Bond energy?

A

Energy needed to break a bond between 2 atoms

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12
Q

What units are bond energies measured in?

A

kJ/mol

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13
Q

You can use bond energies to work out…

A

the energy change for most reactions

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14
Q

When new bonds are formed between atoms….

A

energy is released

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15
Q

Energy must be supplied to…

A

break chemical bonds

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16
Q

What is an exothermic reaction?

A

One that gives out energy to the surroundings

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17
Q

What is an endothermic reaction?

A

One that takes in energy from the surroundings

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18
Q

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

A

Energy is required (endothermic)

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19
Q

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

A

Energy is released (exothermic)

20
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

21
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

22
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

23
Q

How does a catalyst increase the rate of reaction?

A

By lowering the activation energy

24
Q

READ ONLY:

How do you work out total energy change?

A

• total for breaking bonds: no. of bonds x breaking bond energy
• total for making bonds: no. of bonds x making bond energy
• total energy change: breaking bonds - making bonds

25
Q

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

A

The reaction is endothermic

26
Q

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

A

The reaction is exothermic

27
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

28
Q

How can a simple cell be made?

A

By connecting two different metals in contact with an electrolyte

29
Q

What do batteries consist of to provide a greater voltage?

A

Two or more cells connected

30
Q

What chemicals are cells made from?

A

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

31
Q

What is the electrolyte in a cell made of?

A

Ammonium chloride

32
Q

What is the anode made of in a cell?

A

Zinc casting

33
Q

What does the voltage produced by a cell depend on?

A

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

34
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

35
Q

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

A

The more reactive metal

36
Q

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

A

There will be a higher voltage produced

37
Q

Are alkaline batteries rechargeable?

A

No

38
Q

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

A

The chemical reactions stop

39
Q

What happens to the chemical reactions in rechargeable batteries?

A

They are reversed using an external electrical current

40
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

41
Q

What hydrogen fuel cells offer an alternative to?

A

Fossil fuels and rechargeable cells and batteries

42
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

43
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

44
Q

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

A

• provide water
• efficient
• no moving parts
• lightweight

45
Q

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

A

H2 -> 2H+ + 2e-

46
Q

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

A

02 + 4H2+ 4e- > 2H20

47
Q

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

A

2H2 + 02 →> 2H20

GCSE AQA Chemistry (21 decks)

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