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Z. Higher Chemistry > Unit 3 > Flashcards

Unit 3 Flashcards

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1
Q

How are industrial processes designed?

A

Industrial processes are designed to maximise profit and minimise the impact on the environment.

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2
Q

Factors influencing industrial process designed (5)

A

(Many people eat old apples)

  • Marketing of by-products
  • product yield
  • energy requirements
  • opportunities for recycling
  • availability, sustainability and cost of feedstocks
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3
Q

What are environmental factors when designing industrial processes

A

Minimising waste

Avoiding the use of or production of toxic substances

Designing products which will be biodegradable if appropriate

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4
Q

What is the difference between % yield and atom economy?

A

The % yield is used to compare the yield of a product actually obtained with what could have been obtained in theory if all the reactants were converted into products with no waste.

The % atom economy is a measure of the % of reactant that becomes useful products. Atom economy tends to be more used in industry as it tells chemist how efficient a process actually is.

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5
Q

% yield formula

A

% yield = (actual yield / theoretical yield) x 100

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6
Q

Atom economy formula

A

%Atom economy = (mass of desired products / total mass of reactants) x 100

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7
Q

Why must reaction rates be controlled in industrial processes?

A

If reaction rates are too low, the process will not be economical.

If reaction rates are too high, there will be a risk of explosion.

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8
Q

Relative reaction rate formula

A

Rate = 1/t

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9
Q

Factors affecting reaction rates - concentration

A

The higher the concentration, the faster the rate of reaction. There are more reacting particles which means there is a higher chance of collisions so the reaction rate in increased.

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10
Q

Factors affecting reaction rates - particle size

A

The smaller the particles, the faster the reaction. This is because smaller particles provide more surface area for collisions.

Larger reactants - deceased surface area, less collisions, slower rate of reaction.

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11
Q

Factors affecting reaction rates - temperature

A

Increasing temperature increase the rate of reaction because particles have a greater kinetic energy and will move faster and collide more often which will mean more successful collisions because more particles will have an energy equal to or greater than the activation energy.

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12
Q

Factors affecting reaction rates - pressure

A

Increasing pressure (for gaseous reactants) means there are more reactant particles for a given volume so there will be more collisions.

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13
Q

Factors affecting reaction rates - collision geometry

A

Particles must collide with the correct geometry for the reaction to be successful:

E.g. double bond needed

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14
Q

Exothermic reactions

A

Exothermic reactions give a negative enthalpy.

The energy of the product is less than the energy of reactants.

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15
Q

Endothermic reactions

A

Endothermic reactions have a positive enthalpy.

The energy of products is more than the energy of reactants.

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16
Q

Enthalpy change definition

A

Enthalpy change is the difference in energy (enthalpy) between the products and reactants in a reaction.

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17
Q

Activation energy

A

Activation energy is the minimum energy required for a reaction to take place.

For reactions to occur particles need energy equal to or greater than the activation energy.

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18
Q

Activated complex

A

The activated complex as an unstable intermediate arrangement of atoms formed as old bonds are breaking and new bonds are forming.

(It is at the top of the potential energy graph)

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19
Q

How do catalysts affect activation energy

A

Catalyst speed up a chemical reaction by providing an alternative reaction pathway which has a lower activation energy, therefore more particles have energy equal to, or greater than, the activation energy.

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20
Q

Distribution diagrams

A

Energy distribution diagram shows the number of molecules and energy they have.

Only the particles with energy equal to or above the activation energy will take part in the reaction.

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21
Q

Distribution diagram - increasing temperature

A

Increasing the temperature means that the particles will have more energy, so therefore more of them will reach the activation energy.

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22
Q

Distribution diagram - catalyst affects

A

Adding a catalyst will lower the activation energy – therefore more particles will be equal to or greater than it.

23
Q

Enthalpy meaning

A

Enthalpy is a measure of the chemical energy in a substance (KJ)

24
Q

Exothermic meaning and how it affects industry

A

Exothermic reactions releases heat energy to the surroundings. In industry it may require excess heat to be removed to prevent extreme temperature rises or dangerous conditions.

25
Q

Endothermic meaning and how it affects industry.

A

Endothermic reactions take in heat energy from the surroundings. In industry there may be costs involved in supplying heat at the start of the reaction and also maintaining the reaction rate.

26
Q

Enthalpy formula

A

Eh = cm🔺T

27
Q

Enthalpy of combustion definition

A

Enthalpy of combustion is the energy change when one mole of a substance burns completely in oxygen

Units kJmol-1
Values in data book.

28
Q

Hess’ law

A

Hess’ law states that the enthalpy change for a reaction depends on the initial and final stage of the reaction and is independent of the root the reaction takes.

This means that no matter the route taken, the enthalpy change will always be the same for a reaction.

29
Q

Molar bond enthalpy

A

Molar bond enthalpy is the energy required to break one mole of bonds in a diatomic molecule.

30
Q

Mean molar bond enthalpy

A

Mean molar bond enthalpy is the energy required to break one mole of bonds that occur in compounds (not diatomic).

It is an average for all the known compounds that contain a certain bond so it is not exact.

31
Q

Dynamic equilibrium

A

Dynamic equilibrium is when the RATES of a forward and reverse reaction are exactly the same (equal).

32
Q

Closed system

A

Close system as when the reaction is carried out in a sealed container, so no reactants or products are lost.

33
Q

Describe the concentrations of reactants and products at equilibrium

A

At equilibrium the concentrations of reactants and products remain constant but rarely equal.

34
Q

Describe why chemists move the position of equilibrium

A

Chemist in industry often move the position of equilibrium to favour the products and to maximise their profits.

E.g. haber process

35
Q

Factors that affect equilibrium - changing temperature

A

Increasing the temperature favours the endothermic reaction.
(Shifts in the endothermic direction)

Decreasing the temperature favours exothermic reactions.
(Shift in the direction of the exothermic reaction)

36
Q

Factors affecting equilibrium - pressure

A

Changing pressure ONLY affects substances that are in the gaseous state.

Increasing the pressure favours the side with LOWER gas volume.

Decreasing the pressure favours the side with HIGHER gas volume.

37
Q

Factors affecting equilibrium - concentration - What happens when you add a chemical that is a product/reactant

A

Adding any chemical that is a product/reactant or can react with one of them can alter the equilibrium position.

38
Q

Factors affecting equilibrium - concentration - What is the effect of adding a reactant/ removing a product

A

Adding a reactant (or removing a product) will shift equilibrium to the right to compensate the gain/loss.

39
Q

Factors affecting equilibrium - concentration - What is the effect of increasing a product/ decreasing a reactant?

A

Adding a product/removing a reactant will shift equilibrium to the left.

40
Q

Factors affecting equilibrium - concentration - How do neutralisation reactants affect equilibrium

A

Neutralisation reactants can affect equilibrium if the equation contains hydrogen ions or hydroxide ions.

41
Q

Factors affecting equilibrium - concentration - what is the effect of adding NaOH

A

Adding NaOH will add hydroxide ions which can react with the hydrogen ions to form water (therefore adding a reactant)

42
Q

What is the effect of a catalyst on equilibrium

A

 Catalysts have no affect on equilibrium position, however they allow equilibrium to be reached quicker and at a lower temperature.

43
Q

What is chromatography?

A

Chromatography is a method of separating and analysing a mixture of soluble chemical substances.

44
Q

Describe how chromatography works

A

Chromatography is used to separate substances in complex mixtures. It works as substances travel at different speeds due to their polarity or mass.

45
Q

Describe how components can be identified using chromatography

A

Components can be identified by the distance travelled or by the time it has taken to travel through the apparatus (retention time).

46
Q

Describe the term volumetric analysis

A

Volumetric analysis uses a solution of accurately known concentration in a quantitative Reaction to determine the concentration of another solution.

47
Q

State the use of titration experiments

A

Titrations are used to accurately determine the volumes of solution required to reach the endpoint of a chemical reaction.

48
Q

Describe the term standard solution

A

A standard solution is a solution of accurately known concentration.

49
Q

State the use of redox titrations

A

Redox titrations are titrations based on redox reactions and are used to determine the unknown concentration of a solution.

50
Q

Why are indicators not always needed to determine the endpoints of reactions?

A

In some titrations an indicator is not required as the solution may self indicate (change colour itself).

51
Q

Chromatography information for questions - number of compounds

A

The number of compounds in a mixture = number of peaks

52
Q

Chromatography information for questions - amount of each compound present

A

Height of peak

Greater height = more of the compound

53
Q

Chromatography information for questions - retention time

A

Time to travel through apparatus

If in polar solution - polar molecules should have shorter retention time as they are most soluble?
Etc

Z. Higher Chemistry (4 decks)

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