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GCSE chemistry > C5 > Flashcards

C5 Flashcards

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1
Q

Yield of a product

A

Mass of that product made in a chemical process

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2
Q

Theoretical yield

A

The maximum mass it is possible to make from a given mass of reactants

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3
Q

Actual yield

A

Mass of product actually made in a chemical reaction

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4
Q

Percentage yield

A

Actual yield
______________ X 100

Theoretical yield

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5
Q

What factors affect percentage yield ?

A

-reactants reacting in a different way than expect
-reaction may not go to completion ( often happens in reversible reactions)
-may lose some of the product when separating from the reaction mixture of purifying it

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6
Q

Atom economy

A

Sum of Mr of desired product
—————————————— X 100
Sum of Mr of all products

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7
Q

What factors do engineers consider when choosing a reaction pathway

A

-yield of product
-atom economy of reaction
-usefulness of by product
-rate of reaction
-equilibrium position , if it’s a reversible reaction

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8
Q

Epoxyethene

A

C2H4O

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9
Q

What happened to the process of forming epoxyethene ?

A

Original :
Ethanol + chlorine + calcium hydroxide = calcium chloride + water + epoxyethene
Yield of this was 80% but atom economy was very low at 25.4#
Modern :
Ethene + oxygen = epoxyethene
Using silver as a catalyst , yield is 80% but atom economy is 100%

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10
Q

How can by products improve atom economy of a process

A

If they are useful and can be sold
For example , calcium chloride is a useful product in the original process of epoxyethene

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11
Q

How to convert from cm3 to dm3

A

Divide by 1000

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12
Q

How to convert from dm3 to cm3

A

Multiply by 1000

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13
Q

Concentration in g/dm3

A

Mass of solute in g
—————————
Volume of solution in dm3

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14
Q

Concentration in mol/dm3

A

Amount of solute in mol
————————————
Volume of solution in dm3

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15
Q

Molar volume at RTP

A

24dm3/mol

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16
Q

What is molar volume

A

One mole of any substance in the gas state occupies the same volume at the same temperature and pressure

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17
Q

Volume in dm3 at RTP

A

Amount in mol x 24dm3/mol

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18
Q

Amount in mol at RTP

A

Volume in dm3/24dm3/mol

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19
Q

Rate of reaction

A

Amount of reactant used
————————————
Time taken

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20
Q

Rate of reaction

A

Amount of product formed
—————————————
Time taken

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21
Q

How do you measure volume of gas

A

Use an upside down measuring cylinder in water or use a gas syringe

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22
Q

Reaction can only happen if

A

React at particles collide with each other and haven enough energy to react

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23
Q

A collision that leads to a reaction is

A

A successful collision

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24
Q

A collision won’t be successful

A

If the particles have less energy than the activation energy

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25
Q

As the temperature of a reaction increases

A

Particles move more quickly colliding more often , so a greater proportion of colliding particles have the activation energy or more.

26
Q

What is directly proposition to the rate of reaction

A

1/t = rate of reaction

27
Q

What happens to the energy stored in a reaction if temperature / pressure / surface area increases

A

Energy stored in the particles does not change , but , because the rate of collisions increases , the rate of successful collisions increases

28
Q

How do you investigate the effect of concentration on reaction rate ?

A

-reaction between magnesium ribbon and HCL , measure the time taken for magnesium to be used up
-add water to reduce its concentration
- when recording reactions times , you can then calculate 1/time to obtain reaction rates

29
Q

In the reaction between magnesium and HCL , what is the control

A

The magnesium ribbons length and therefore size

30
Q

What happens to a reaction if pressure is increased

A

Particles in the gas state become more crowded , so collide more often

31
Q

What do industrial chemical processes often use to achieve high rates of reaction ?

A

High pressures

32
Q

Why do reactions occur slower with solids

A

Particles in a substance can only vibrate around fixed positions , and cannot move place to place .
-only particles at the surface can take part in collisions

33
Q

As the SA increases

A

So does rate of reaction

34
Q

Why do reactions go faster with powders ( larger SA) ?

A

More reactant particles are available for collisions , collisions are more likely so particles collide more often

35
Q

In a solid , as the size of the lump decreases

A

The surface area to volume ratio increases

36
Q

What is a catalyst ?

A

A substance that increases the rate of a reaction but remains unchanged at the end of the reaction

37
Q

If u add 1g of a catalyst to a reaction mixture

A

There will still be 1g left when the reaction has finished

38
Q

True or false : catalysts can catalyse any reaction

A

FALSE , they are specific to particular reactions

39
Q

Why are catalysts helpful

A

Even though they are very expensive , only a small amount of catalyst will catalyse the reaction between large amounts of reactants

40
Q

What are biological catalysts

A

Enzymes are proteins that catalyse different reactions in biological systems

41
Q

Catalyse

A

Enzyme produced by the liver cells , causes the decomposition of hydrogen peroxide

42
Q

How do catalysts work

A

Catalysts work by providing an alternative reaction pathway with a lower activation energy

43
Q

How do catalysts affect reactions

A

Greater proportion of colliding particles have the activation energy or more
The rate of successful collisions increases compared to the rate in an uncatalysed reaction

44
Q

Reversible reaction

A

The products can react together to from the original reactants

45
Q

Example of a reversible reaction

A

Reaction between Copper (II) sulfate and water
-blue crystals of copper (II) sulfate are hydrated as each cu(II) ion is surrounded by 5 water molecules
-removing these water molecules by heating , you are left with white ANHYDROUS CuSO4

46
Q

What is the forwards reaction hydrated copper sulfate = copper sulfate + water

A

Endothermic reaction , vice versa

47
Q

In the forwards reaction , why is steam produced

A

Because enough energy is transferred by heating

48
Q

What are the conditions required to reach dynamic equilibrium

A

Must be in a closed system

49
Q

Equilibrium

A

When a reversible reaction happens in a closed system , the rates of the forward and backward reaction become equal

50
Q

Dynamic equilibrium

A

Forwards and backwards reactions still happen ( concentrations remain constant ) , but at the same rate

51
Q

Equilibrium position is on the right when

A

Concentration of reactants is greater than the concentration of products

52
Q

When the concentration of reactants is less than the concentration of the products

A

Equilibrium position lies on the left

53
Q

If pressure is increased

A

Equilibrium moves to the side where there are fewest moles of gas

54
Q

If concentration is increased

A

Equilibrium position moves in the direction away from the substance

55
Q

If temperature is increased

A

Equilibrium moves in the direction of the endothermic change

56
Q

Equilibrium yield

A

Amount of desired product present in a reaction at equilibrium
Depends on the pressure and temperature and concentration of the reactants

57
Q

Why do you need to supply plenty of reactants to make plenty of product

A

So equilibrium position moves to the right

58
Q

Le Chateliers principle

A

When a change is made to a reaction at equilibrium , the position of equilibrium moves to oppose that change

59
Q

What are the disadvantages of using a very high pressure

A

-requires expensive equipment
-lot of energy to run
-hazardous
-requires tough reaction vessels to withstand pressure

60
Q

What are the disadvantages of using a low temperature

A

-rate of reaction is too low to be profitable

61
Q

Volume

A

Moles x 24

62
Q

Volume

A

Moles x molar volume

GCSE chemistry (3 decks)

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