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Pro Chem > C7 > Flashcards

C7 Flashcards

1
Q

How is energy moved around in?

A

Chemical reactions

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2
Q

Do chemicals store differnt amount of energy?

A

Yes

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3
Q

What happens if the products of a reaction store more energy than original reactants.

A

They must have taken in the differnce in energy between the products and reactants of the surrounding during the reaction

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4
Q

What happens if they store less than the original reactants?

A

The excess energy was transfered to the surroundings during the reaction.

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5
Q

Why does the overall energy not change?

A

Energy is conserved in reactions

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6
Q

Can energy be created or destroyed?

A

No, only moved around

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7
Q

What’s an exothermic reaction?

A

When heat is transfered to the surroundings

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8
Q

How is exothermic reaction shown?

A

A rise in temperature

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9
Q

What’s the best example of an exothermic reaction?

A

Burning fuels (combustion)

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10
Q

What does combustion do ?

A

Gives out a lot of energy

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11
Q

What is also exothermic?

A

Neutralisation reactions

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12
Q

What are the everyday uses of exothermic reaction?

A

Self heating cans of hot, chocolate and coffee

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13
Q

What is an endothermic reaction?

A

A reaction which takes in energy from the surroundings

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14
Q

How is an endothermic reaction shown?

A

By a fall in temperature

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15
Q

What are some examples of an endothermic reaction?

A
  • The reaction between citric acid and sodium hydrogencarbonate
  • Thermal decomposition
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16
Q

What are some everyday uses of endothermic reactions?

A
  • Sports injury packs ( Makes the pack instantly cooler without putting in freezer )
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17
Q

Can energy transfered be measured?

A

Yes

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18
Q

How can you measure the energy released?

A

By a chemical reaction. (Take the the temperature of the reagents mix them in a polystyrene cup and measure the temperature of the solution at the end

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19
Q

What’s the biggest problem with energy measurements?

A

The amount of energy lost to the surroundings

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20
Q

How can you stop emergy going to the surroundings?

A

Put the polystyrene cup into a beaker of cotton wool to give more insulation and putting a lid on can reduce evaporation

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21
Q

How can you test the effect of acid concentration on the energy released in a neutralisation reaction between HCL and NaOH?

A

1) put 25cm3 of 0.25mol/dm3 of hydrochloric acid and sodium hydroxide in seperate beakers
2) Put both beakers in a water bath and set to 25°c. Wait for both to reach same temperature
3) Add the HCl followed by NaOh to the polystyrene cup with a lid
4) take the temperature every 30 seconds and record the highest temperature
5) Repeat steps 1-4 using 0.5mol/dm3 and them 1 mol/dm3

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22
Q

Whats the equipment needed for the endothermic and exothermic reaction?

A

Polystyrene cup
Cotton wool
Themometer
Reaction mixture
Lid
Large beaker

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23
Q

What do reaction profiles show?

A

Energy changes

24
Q

What a reaction profiles?

A

Diagrams that show relative energies of the reactants and products in a reaction. And how energy changes in a reaction

25
Q

What does the difference in height show in a reaction profile?

A

The energy given out per mole

26
Q

What is a dip in the graph?

A

Exothermic

27
Q

Whats the start to the peak lf the graph?

A

The activasion energy

28
Q

What is the activasion energy?

A

Minimum amount of energy the reactants need to collide with each other.

29
Q

What does greater the activasion energy mean?

A

More energy needed to start the reaction

30
Q

What is the graph when products are higher than reactants?

A

Endothermic

31
Q

What’s the difference in height of the endothermic graph?

A

The energy absorbed

32
Q

What must be always supplied to break bonds?

A

Energy

33
Q

During a chemical reaction what happens?

A

Old bonds are broken and new bonds are formed

34
Q

What is bond breaking?

A

Endothermic

35
Q

What is making new bonds?

A

Exothermic

36
Q

What do chemical reactions in a cell produce?

A

Electricity

37
Q

What’s an electrochemical cell?

A

A basic system made up of 2 different electrodes in contact with an electrolyte.

38
Q

What should the 2 electrodes in a cell be able to do?

A

Conduct electricty and are usually metals

39
Q

What can be used to measure the volatge of a cell?

A

A volt meter

40
Q

What does the bigger the difference in reactivity mean?

A

The bigger the voltage of the cell

41
Q

Why would the electrolyte used in the cell affect the size of the voltage?

A

Different ions in a solution will react differently with the metal electrodes used

42
Q

How is a battery formed?

A

By connecting 2 or more cells in a series.

43
Q

Why are the voltages combined?

A

So there is a bigger voltage overall

44
Q

What happens to non rechargable batteries?

A

The reactants get used up

45
Q

What happens overtime in the reacting particles?

A

The ions in the metal ion on the electrode get used up and turned into products

46
Q

How can rechargable batteries be used again?

A

The reaction can be reversed by connecting it to an external current

47
Q

What is used to produce electrical energy?

A

Fuel cells used fuel and oxygen

48
Q

What is a fuel cell?

A

An electrical cell that’s supplied with fuel and oxygen and uses energy from the reaction to produce energy effefficiently

49
Q

What happen when fuel entes the cell?

A

It becomes oxidised and sets up a potential difference

50
Q

Whats involved in hydrogen oxygen fuel cells?

A

A redox reaction

51
Q

With dealing with fuel cells whats the other way round?

A

Anode and cathode

52
Q

What happens at hydrogen oxygen fuel cells?

A

1) hydrogen goes in anode compartment
2) oxygen goes cathode compartment
3) At the -ve(anode) hydrogen loses electrons to produce H+ ions ( oxidation)
4) H+ ions move to the cathode
5) At the cathode oxygen gains electrons and reacts with (H+ ions) to make water this is reduction
6) the overall reaction is hydrogen + oxygen = water

53
Q

What can be used in vehicles?

A

Hydrogen oxygen fuel cells

54
Q

What has a finite supply?

A

Conventional fuels

55
Q

Why is using hydrogen oxygen fuel cells better?

A
  • Fuel cells don’t produce that many pollutants as other fuels
  • No green house gases,Nitrogen oxides
    -the only by products is water and heat
56
Q

Disadvantage to hydrogen fuel cells?

A
  • Hydrogen is a gas and takes up more space than a rechargeable battery
  • Hydrogen is explosive when mixed with air
  • the hydrogen fuel is made from hydrocarbons
57
Q

Disadvantage of electric cars?

A
  • Batteries store less energy than fuel cells and need to be refharged often which takes time
  • There is a limit on how many times they can be recahrged before replacing

Pro Chem (11 decks)

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