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Chemistry H > Unit 3 > Flashcards

Unit 3 Flashcards

1
Q

What are industrial processes designed to do?

A

Maximise profit and minimise the impact on the environment

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2
Q

Environmental considerations of industrial processes

A

-Minimise waste
-avoid the use or production of toxins substances
-designing products which will biodegrade if appropriate

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3
Q

Factors influencing industrial process design

A

-availability, sustainability and cost of feedstock (s)
-opportunities for recycling
-energy requirements
-marketability of by-products
-product yield

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4
Q

Feedstock

A

a chemical used to make other chemicals

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5
Q

Raw material

A

a substance that is removed from the planet and processes to make the feedstock

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6
Q

by-product

A

a product also made in the reaction which isn’t the main desired product

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7
Q

What is percentage yield?

A

The percentage of product you made compared to how much you should have made

% yield=actual yield/theoretical yield x100

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8
Q

How can percentage yield be improved?

A

-avoid wastage
-use more pure reactants (as reactants contain impurities)
-use the most accurate equipment for our measurements

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9
Q

What is atom economy?

A

A measure of the proportion of reactant materials/converted in the final desired product

AT=mass of desired product/total mass of reactants x100

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10
Q

Excess calculations

A

-In a chemical reaction with more than one reactant
-A reaction stops when one of the reactants is used up
-There is (almost always) a reactant which there is far too much of—>in excess
-In order to ensure that costly reactant(s) are converted into product, an excess of less costly reactant(s) can be used
-The other reactant dictated how much product is made and the one we use for mole ration—>limiting reagent

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11
Q

What is the molar volume of a gas?

A

Its volume per mile (litres per mol)

Same for all gases at the same temperature and pressure

Value is temperature and pressure dependent

mv=V/n

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12
Q

Why do reaction rates have to be controlled in industrial processes?

A

If the rate is too low then the process will not be economically viable

If the rate is too high there will be a risk of explosion

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13
Q

What are the conditions required for chemical reactions to go ahead to form products

A

Particles collide with each other
—>
-collisions have enough energy
-correct orientation

COLLISION THEORY

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14
Q

5 ways to change rate of reaction

A

-particle size/surface area
-concentration
-temperature
-pressure (gases only)
-using catalysts

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15
Q

What happens when the Surface area is changed?

A

increase surface area—>speed of reaction increases

more surface area—>bigger area for collisions to occur

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16
Q

What happens when the Concentration is changed?

A

increase concentration—>speed of reaction increases

more particles—>more collisions—> more successful collisions

Reaction progresses—>reactants get used up—>less possible collisions—> rate decreases

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17
Q

What happens when the Temperature is changed?

A

Temperature increases—>speed of reaction increases

higher temperatures—>more energy—>faster movement—>more successful collisions

kinetic energy is increased—>pushing more molecules over the activation energy and increasing the speed of reaction

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18
Q

What happens when the Pressure is changed?

A

Pressure increases—>spread of reaction increases

high pressure—>smaller space—> more collisions—>more successful collisiobs

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19
Q

What is enthalpy?

A

-Energy stored in the bonds of molecules
-Enthalpy must be involved when a chemical reaction proceeds

-A measure of the chemical energy in a substance
-For industrial processes chemists must be able to predict the enthalpy change
-Endo may be costly as heat energy must be supplied
-Exo can lead to thermal explosions if heat energy is not removed preventing a rise in temp

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20
Q

Graph-reactant lower than product

A

The reactants need extra energy to equal the energy of the products so have to take energy from around it
-endothermic +

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21
Q

Graph-reactants higher than products

A

The reactants have too much energy to make the products so they have to disperse it
-exothermic -

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22
Q

🔺H=

A

H products - H reactants

To find energy required to make the products

23
Q

What is activation energy?

A

Energy required for reactants to become products

Ea

The minimum energy required by colliding particles to form an activated complex and can be calculated from potential energy diagrams

24
Q

What is the activated complex?

A

An unstable arrangement of atoms formed at the maximum of the potential energy barrier during a reaction

25
Q

Catalysts

A

Lower the activation energy required for a reaction, making it easier to form the activated complex to form

Enthalpy does not change

26
Q

Relative rate

A

R=1/t

27
Q

Increasing temperature effect

A

increases kinetic energy, pushing more molecules over the activation energy and increasing the speed of reaction

28
Q

Catalyst effect

A

Reduce activation energy, meaning now more particles have energy above the sea, so more successful collisions will lead to a faster reaction

29
Q

What is the enthalpy of combustion of a substance?

A

The enthalpy change when one mole of the substance burns completely in oxygen

30
Q

Molar bond enthalpy

A

The energy required to break one mole of bonds in a diatomic molecule

31
Q

Mean molar bond enthalpy

A

The average energy required to break one mole of bonds, for a bond that occurs in a number of compounds

32
Q

What can bond enthalpy we be used for?

A

To estimate the enthalpy change occurring for a gas phase change reaction

By calculating the energy required to break bonds in the reactants and the energy real eased when new bonds are formed in the products

33
Q

What if C is given in solid form for enthalpy of combustion?

A

DATA BOOKLET
BOTTOM OF P11

34
Q

What does Hess’ Law state?

A

That the enthalpy change for a chemical reaction is independent of the route taken

35
Q

In a closed system, when do reversible reactions attain a state of dynamic equilibrium?

A

When the rates of the forward and reverse reactions are equal

36
Q

At equilibrium, what are the concentrations of reactants and products?

A

They remain constant but are rarely equal

37
Q

Which is endo and which is exo?

Bonds forming and bonds breaking

A

bonds forming-exo
bonds breaking-endo

38
Q

What happens when you increase and decrease the temperature of an equilibrium

A

Increase-equilibrium shifts to the endo sidetaking in extra heat

decrease-equilibrium shifts to exo side releasing heat

39
Q

What happens if you increase concentrations of products and reactant in an equilibrium?

A

Reactants-shifts to the right to use reactants up

Products-shifts to the left

40
Q

What to look out for being added to an equilibrium?

A

acids
alkalis
silver nitrate and silver halides (precipitate) -> if a halide is in reaction

41
Q

What do catalysts do to an equilibrium?

A

Speed up how quickly equilibrium is established but do not change the position

42
Q

What substances are affected by pressure?

A

gases

43
Q

What happens when you increase pressure of an equilibrium?

A

Shifts to the side where there are less moles of gaseous substances

44
Q

What is chromatography?

A

A technique used to separate the components present within a mixture.

It separates substances by making use of differences in their polarity or molecular size (bigger molecules travel shorter distances)

45
Q

Chromatography-How can the identity of a component be indicated?

A

Either by distance travelled or by the time it has taken to travel through the apparatus (retention time)

46
Q

Rf=

A

distance travelled component/distance travelled by solvent

47
Q

Why is pencil used in chromatography?

A

If ink was used the solvent will carry it too

48
Q

Gas chromatography

A

Uses an inert (unreactive) gas

The larger the peak the more of the substance present

If detector is overloaded (cannot see full peak) this means we need to:
-inject less of the sample
-dilute the sample

larger samples (formula mass is larger) will appear later

49
Q

What does volumetric analysis involve?

A

using a solution of accurately known concentration in a quantatative reaction to determine the concentration of another substance

50
Q

What is titration used to determine, accurately?

A

The volumes of solution required to reach the end-point of a chemical reaction

51
Q

What is an indicator used to show?

A

When the end-point of a reaction is reached. Titre volumes within 0.2cm^3 are considered concordant

52
Q

What is a standard solution?

A

A solution of accurately known concentration

53
Q

Preparation of standard solution

A

The weighed sample is dissolved in a small volume of deionised water in a beaker and the standard solution is transferred to a standard flask. The beaker is rinsed and the rinsing also poured into the standard flask

The flask is made up to the mark adding the last few drops of water using a dropping pipette. The flask is stoppered and inverted several times to ensure through mixing of the solution

We use deionised water because tap water contains dissolved salts that may react with our sample and affect the concentration of the solution

54
Q

How to prepare a burette for titration?

A

rinse the burette with the solution to be put in it

fill burette above the scale with solution

filter funnel used should be removed

tap opened/some solution drained to remove air bubbles

solution run into scale reading should be made from the bottom of meniscus

Chemistry H (11 decks)

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