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Chemistry C3 > Reversible reactions and hydrocarbons > Flashcards

Reversible reactions and hydrocarbons Flashcards

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1
Q

What is a reversible reaction?

What letter equation shows this?

A

On where the products of the reaction themselves react to produce the original reaction. (It goes both ways.)
A+B (reversible reaction sign) C+D

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2
Q

What will happen if a reversible reaction happens in a closed system (rates and equ)?

A

A state of equilibrium will always be reached

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3
Q

What does ‘reaching a state of equilibrium’ mean?

A

The amounts of the reactants and products will reach a certain balance and stay there.

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4
Q

What does a closed system mean?

A

No reactants or products can escape.

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5
Q

In an equilibrium what is the effect of the two reactions and why?

A

None, because the reactions are taking place in both directions, and the forward and reverse reaction cancel each other out.

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6
Q

How fast are the forward and reverse reactions taking place?

A

Exactly the same rate in both directions

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7
Q

Reversible reactions always reach an …. eventually, but by changing the …. you can change the position of …. so that you end up with more ….. for example.

A

equilibrium

conditions, equilibrium, products

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8
Q

What does the position of equilibrium strongly depend upon? (2)

A

the temperature and pressure surrounding the reaction

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9
Q

What does the position of equilibrium mean?

A

The relative amounts of reactants and products

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10
Q

If you deliberately alter what?…. you can move the what? … to give what?

A

the temperature and pressure, the position of equilibrium, more product and less reactants

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11
Q

All reactions do what with energy on way, and the other the other ways.

A

Exothermic in one direction, endothermic in the other

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12
Q

What happens if you raise the temperature of of a reaction?

A

The ENDOthermic reaction will increase in rate to use up the heat

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13
Q

What happens if you reduce the temperature of of a reaction?

A

The EXOthemric reaction will increase to give out more heat

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14
Q

Many reactions have a greater … on one side, either of its …. or ….. .

A

volume, reactants or products

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15
Q

What happens if you raise the pressure of of a reaction?

A

It will encourage the reaction which produces less volume

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16
Q

What doesn’t a catalyst do in a reaction?

What does it do?

A

Change the position of equilibrium

Speed up both the forward and backward reactions by the same amount

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17
Q

So if you add a catalyst what does this mean for the reaction?

A

It reaches equilibrium quicker but you end up with the same amount of product as with out one.

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18
Q

The Haber process produces what used for what?

A

Ammonia, NH₃, to make fertilisers

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19
Q

What are the two reactants for ammonia?

What is the symbol equation?

A

Hydrogen and nitrogen

N2 (g) 2H2 (g) = (reversible reaction sign) 2NH₃ (g) (+heat)

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20
Q

Where is the nitrogen found for ammonia?

Where does the hydrogen come from?

A

The air, which is 78% nitrogen.

Natural gas or from crude oil

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21
Q

What happens in the reaction of ammonia and hydrogen?

What does the reaction reach?

A

Hydrogen and nitrogen react to form ammonia, but as it’s reversible some ammonia breaks down again into the reactants, the reaction reaches an equilibrium.

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22
Q

What are the industrial conditions for making ammonia?
Pressure
Temp
Others

A

Pressure: 200 atmospheres
Temp: 450 degrees
Catalyst: Iron

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23
Q

Why is higher pressure favoured by the left hand side of the reversible reaction to make ammonia?
So what is the pressure set at because of this? to get what? So the pressure is set at …. because if it were……?

A

There are four molecules of gas on the left when only 2 on the right, so the higher pressure will favour this side as it creates less product, one of the rules for pressure.
“if you raise the pressure it encourages the reaction that makes less volume” - this one.
As high as possible to give the best %yield without making the plant to expensive to build, so 200 atmospheres is the operating pressure.

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24
Q

The forward reaction is …. thermic.
So what will increasing the temperature do, why?
So the yield of ammonia will be greater at … temperatures.

A

Exothermic
Move the equilibrium the wrong way, towards making the reactants, not the ammonia, as the endothermic will use the extra heat and react more.
Lower

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25
Q

What is the problem with lower temperatures for making ammonia?
So what do they do anyway?

A

Lower rate of reaction

Increase the temp to get a faster rate of reaction.

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26
Q

What is 450 degrees in the Haber process a compromise between? Give an example of how increased temp is better…

A

Rate of reaction and and maximum yield.

It’s better to wait 20 seconds for 10% yield, than 60 secs for a 20% yield.

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27
Q

How is the ammonia gas converted into a liquid?

Where does the unreacted hydrogen and nitrogen go?

A

It is condensed by cooling in the liquefier and is removed

Recycled so nothing is wasted by rising up to the top of the reaction vessel to react again.

28
Q

What does the iron catalyst do in the Haber process?
Which gets it to its….
With out catalysts what would happen?

A

Makes the reaction go faster
…equilibrium proportions more quickly but doesn’t affect the position of the equilibrium.
The temp would have to be raised even further to get a quick enough reaction and that would reduce the % yield further.

29
Q

What is the general formula for alcohols?

A

CnH2n+1 OH

30
Q

What is the alcohol functional group?

A

-OH

31
Q

What is a homologous series?

A

A group of chemicals that react in a similar way because they have the same functional group.

32
Q

What is the chemical formula for the first three alcohols?

A

CH3OH, C2H5OH, C3H7OH

33
Q

What are the similar properties of alcohols? (4)

A

They are all flammable, burning in air to produce CO2 and H2O
They dissolve completely into water to form neutral solutions
They react with sodium to give hydrogen and alkoxides
Ethanol is the main alcohol in alcoholic drinks as it’s not as toxic as methanol which causes blindness but still damages the liver and brain.

34
Q

What is the symbol and word equation for the burning of methanol?

A

2CH₃OH (l) + 3O2 (g) = 2CO2 (g) + 4H2O

Methanol + Oxygen = Carbon dioxide + water

35
Q

What is the symbol and word equation for the reaction of sodium and alcohol to give hydrogen and alkoxides?

A

2C2H5OH (l) + 2Na (s) = 2C2H5OHNa (aq) + H2 (g)

Ethanol + Sodium = sodium ethoxide + Hydrogen

36
Q

What is one very useful industrial application of alcohols?

Why?

A

As solvents - they can dissolve most compounds that water dissolves as well as ones water can’r such as oils, fats and hydrocarbons

37
Q

Ethanol is the solvent for what household items?

What two things can it do so it’s used for these?

A

Perfumes and aftershave lotions.

Mix with the oils that give the smell and the water which makes up the bulk of the product

38
Q

What is methylated spirit?
What are they used for?
How is it dangerous, how are people stopped from drinking it?

A

Ethanol with chemicals added to it.
Cleaning paint brushes and for fuel.
It’s poisonous to drink so a purple-blue dye is added

39
Q

Where is ethanol used as a fuel?

A

In spirit burners as it’s burns cleanly and isn’t smelly

40
Q

Where is ethanol used as a fuel after being mixed with what?

What’s good about this?

A

It’s mixed with petrol and used for cars

As it burns cleanly the more added to the fuel the less pollution produced

41
Q

Where is ethanol used as a fuel?

What is one BIG advantage?

A

In Brazil
As they have little oil but lots of land they grow lots of sugar cane and ferment it to get ethanol to burn
It is a renewable source

42
Q

What is the carboxylic acid functional group?

What does it look like?

A

COOH
C in the middle, on one arm are two lines joining the first O then on the other side one arm joining the OH next to each other.

43
Q

What do the names of the carboxylic acids end in?

A

-anoic acid.

44
Q

What are the first three alcohols in order?

A

Methanol, ethanol, propanol

45
Q

Give the chemical formula for methanoic acid….
ethanoic acid….
propanoic acid….

A

HCOOH
CH3COOH
C2H5COOH

46
Q

How do carboxylic acids react?

A

Like any other acid, they react with with carbonates to produce CO2 and a salt

47
Q

What do the salts formed by carboxylic acids reacting with carbonates end in??
What is the word equation for ethanoic acid + sodium carbonate

A

-anoate

= carbon dioxide + sodium ethanoate

48
Q

Carboxylic acids dissolve in water to produce what?
When they dissolve what happens?
But because they don’t do what? not many what are released? so they just form what?

A

Acidic solutions.
They ionise and release H+ ions responsible for making the solution acidic.
Ionise completely, not many H+ are released. Weak acidic solutions

49
Q

The strength of an …. isn’t the same as its ….. . Concentration is how ….. ….. the …. is and strength is how well it is …. in water.

A

acid
concentration
watered down, acid
ionised

50
Q

How do weak Carboxylic acids compare in pH to aqueous solutions of strong acids with the same concentration?

A

The pH is higher (less acidic), of Carboxylic acids, than of the strong acid.

51
Q

How can enthanoic acid be made?
What causes this to be made and how? how else can it be … ?
What is the word equation?

A

Oxidising ethanol
Yeast ferment the ethanol
Oxidised using other oxidising agents
Ethanol + oxygen = Ethanoic acid + water

52
Q

How is vinegar made?

What is this used for? (2)

A

Ethanoic acid is dissolved into water

Flavouring and preserving foods

53
Q

What is the carboxylic acid present in oranges and lemons?
What is it manufactured for?
What else is it used for?

A

Cirtric acid
In large quantities to make fizzy drinks.
To get rid of scale.

54
Q

What type of carboxylic acids are used to make soaps and detergents?

A

Ones with long chains of carbon atoms

55
Q

What are carboxylic acids used for for?

A

The preparation of esters

56
Q

Ethanoic acid is a good …. for many …. molecules.

But is not usually chosen as one because it makes the …. ….

A

solvent, organic

solution acidic.

57
Q

What are esters formed from?

A

An alcohol and a carboxylic acids

58
Q

What is used in the reaction to make an ester?
What is the concept equation for making an ester?
What is the word equation for ethanoic acid + ethanol?

A

An acid catalyst, sulphuric acid e.g
Alcohol + carboxylic acid = ester + water
Ethyl ethanoate + water

59
Q

What is the ester functional group?

What do ester’s names end in? What forms the first part of the ester’s name? What forms the second part?

A

COO

oate, the alcohol used, the acid used

60
Q

Many esters have what kind of smell?

A

Nice sweet and fruity.

61
Q

What does volatile mean, what is volatile (2)?
So because they’re volatile what are they good for?
However what is the problem with these?

A

easily evaporated at normal temperatures, esters and bromine
perfumes as the evaporated molecules are detected by your nose
they’re very flammable, and as they’re highly volatile it makes them very dangerous

62
Q

What do esters not do well?

But what do they do well?

A

Mix with water as they aren’t very soluble

Mix well with alcohols and other organic solvents

63
Q

Esters smell nice so they’re used in ….
They are also used to make …. and ….
Some esters are used in …., e.g … …
Others are used as … for (4)

A

perfumes
flavourings and aromas
ointments, deep heat smell
solvents, paint, ink, glue, and in nail varnish remover

64
Q

What four things do you need to think about when using esters?

  1. In you
  2. Flash
  3. Blue smarties
  4. However….
A
  1. Inhaling the fumes as some esters irritate mucous membranes in the nose and mouth
  2. Ester fumes are heavier than air and are very flammable. Flammable vapour + naked flame = flash fire
  3. Some are toxic especially in large doses, so people worry about health problems associated with synthetic food additives such as esters
  4. They aren’t as volatile or toxic as some organic solvents and don;t release as many toxic fumes as them, so some esters have replaced solvents such as toluene in many paints and varnishes.
65
Q

Explain how a state of equilibrium is reached in a reversible reaction:

A

When the rate of the forward reaction is exactly the same as the rate of the backwards reaction

Chemistry C3 (7 decks)

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