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Higher Chemistry Prelim > Unit 3 Chemistry in Society > Flashcards

Unit 3 Chemistry in Society Flashcards

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1
Q

What are the factors that influence the design of the processes?

A
  • Availability / sustainability of feedstocks
  • opportunities for recycling
  • energy requirements of the process
  • yield of the process
  • marketability of by-products
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2
Q

What are some of the environmental considerations that must be taken into account when creating a chemical process?

A
  • minimising waste
  • Avoiding the use of toxic or corrosive substances
  • designing products that will biodegrade if appropriate
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3
Q

What is meant by a feedstock?

A

The raw materials in a chemical process that are reacted to in a plant to produce the products required

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4
Q

Why is the availability / sustainability of feedstocks important when designing a chemical process?

A

As money can be saved by using local feedstocks, this saves money from transport and also cuts down on the environmental impact of the process and there are less safety considerations about the transport of the feedstocks

  • Feedstocks that are very expensive can cause a loss in profit and alternative feedstocks must be used
  • Feedstocks that are subject to changing prices like natural gas and oil can be expensive and cause loss of profit
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5
Q

Why are opportunities for recycling taken into account when designing a chemical process?

A

Because profit can be gained when you successfully recycle as this means that you use less feedstock to produce your product, meaning that you don’t have to spend as much on buying feedstocks

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5
Q

Why are opportunities for recycling taken into account when designing a chemical process?

A

Because profit can be gained when you successfully recycle as this means that you use less feedstock to produce your product, meaning that you don’t have to spend as much on buying feedstocks

Profit is lost when you don’t recycle products as the unreacted reactants are expensive to remove from the products and this is a waste of feedstocks

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6
Q

Why are Energy requirements taken into account when designing a chemical process?

A

As profit can be gained by using exothermic reactions to provide heat energy for other processes in the plant that are endothermic and require heat energy.

Profit can be lost as gas and oil are subject to fluctuating prices and this can cost a chemical industry lots of money.

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7
Q

Why must Marketability of by-products be considered when designing a chemical industry?

A

The marketability of by-products can gain profit if you are able to re-use byproducts in other chemical processes in the plant or if you are able to sell the by-products to another industry to make money

Profit can be lost when you need to spend money to deal with toxic or corrosive substances such as sulfur dioxide

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8
Q

Why is product yield taken into account when designing a chemical process?

A

Profit can be gained if the process has a high yield as more of the products can be produced meaning more product can be sold and more profit made

Profit can be lost if the process has a low yield meaning that to produce sufficient product you would need to waste more time and money repeating the process to produce enough product

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9
Q

What is atom economy?

A

Atom economy is the mass of the product you want as a percentage of all the reactants used in the reaction

It is a measure of how wasteful a reaction is, reactions with low atom economies are wasteful and produce too much by-product

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10
Q

What is percentage yield?

A

Percentage yield is a measure of how much product was produced as a percentage of the theoretical value of the products produced

Percentage yield is only concerned with the desired product and does not take into account the waste product

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11
Q

What are some of the reasons why a reaction may not have a high percentage yield?

A
  • Side reactants
  • The products not being pure enough
  • The reaction being in equilibrium
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12
Q

What is the role of a catalyst?

A

Increases the rate of a chemical reaction by providing an alternative route with a lower activation energy.

This lowers the energy requirements of the chemical process

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13
Q

What are the Ideas of excess?

A

In most chemical reactions there will be a reactant that is known as the limiting factor and the factor that is not limiting the reaction is in excess

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14
Q

What factor is considered when deciding which reactant in a chemical process should be in excess?

A

Cost of the reactant, with the cheapest reactant usually being the one in excess

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15
Q

What is meant by the term molar volume?

A

The volume of one mole of a gas?

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16
Q

What can be said about the molar volume of gases under the same conditions of temperature and pressure?

A

Under the same conditions of temperature and pressure the molar volume of gases is the same

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17
Q

What is collision theory?

A

collision theory is a principle that states that for a reaction to take place the reacting particles must collide with sufficient energy to break existing chemical bonds and form new ones, and that the reactant particles must collide with the correct collision geometry

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18
Q

What does decreasing particle size do to the rate of a reaction?

A

Decreasing particle size increases surface area of the reactants, this increases the rate of the reaction

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19
Q

What does increasing the concentration of a solution in a chemical reaction do to the reaction rate?

A

As the concentration increases more reactant particles are introduced increasing the frequency of collisions, this increases the total number of successful collisions this increases the rate of the reaction

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20
Q

What effect does increasing the temperature have on the rate of a chemical reaction?

A

Increasing temperature increases both the frequency and energy with which collisions happen, this increases the rate of chemical reactions

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21
Q

What is meant by the term enthalpy?

A

The chemical energy stored in chemicals

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22
Q

What causes enthalpy changes?

A

Reactions, as existing chemical bonds are broken requiring energy and new chemical bonds are formed releasing energy

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23
Q

What will happen if reactants collide with incorrect collision geometry?

A

The reaction will not take place

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24
Q

What can be said about the enthalpy of the products compared to the reactants in an endothermic reaction?

A

In an endothermic reaction the enthalpy of the products will be higher than the enthalpy of the reactants
(as energy is absorbed from the surroundings)

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25
Q

What can be said about the enthalpy of the products compared to the reactants in an exothermic reaction?

A

The products of an exothermic reaction have less energy than the reactants
(as energy is released)

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26
Q

What is meant by an exothermic reaction?

A

A reaction which releases heat energy

27
Q

What is meant by an endothermic reaction?

A

A reaction that absorbs heat from its surroundings

28
Q

How do catalysts lower the activation energy of a reaction?

A

By providing an alternative reaction pathway for the reaction

29
Q

What is temperature?

A

Temperature is a measure of the average kinetic energy of particles in a chemical

30
Q

What is meant by the activation energy?

A

The activation energy is the minimum amount of energy required for a successful collision to occur

31
Q

Why does the apparatus used at national 5 to calculate heat energy not give an accurate value?

A
  • Evaporation of the alcohol
  • The non-uniform distribution of heat
  • Heat loss from the system
  • Incomplete combustion taking place
  • Not all of the energy produced by the fuel will be transferred to the water
  • There could be errors in temperature, volume, or mass measurements
32
Q

Why is a bomb calorimeter efficient at calculating the heat energy?

A
  • Heat is evenly distributed
  • A supply of oxygen is provided to ensure that the fuel does not undergo incomplete combustion
  • The water completely surrounds the area where combustion occurs meaning that most of the heat energy will be transferred to the water
33
Q

What is meant by the term bond enthalpy?

A

Bond enthalpy can be described as the energy required to break one mole of bonds in one mole of gaseous molecules

34
Q

Why are all individual bond enthalpies positive?

A

As breaking bonds is an endothermic process meaning that it requires energy to do

35
Q

What are the units of bond enthalpies?

A

kilojoules per mole (kJ mol-1)

36
Q

What is meant by the term enthalpy of combustion and what is the equation used to find this?

A

Enthalpy of combustion is defined as the enthalpy change when one mole of a substance burns in oxygen at a standard temperature and pressure

37
Q

Why are all of the enthalpy of combustion values given as negative values?

A

As all combustion reactions are exothermic, meaning that all of these reactions give out heat (heat is lost hence negative)

38
Q

What is the equation that will give you the enthalpy of combustion?

A

Enthalpy of combustion = Eh/n

39
Q

What are the principles outlined by Hess’s law?

A

The enthalpy change of any chemical reaction is independent of the route provided that the starting and final conditions are the same.

40
Q

What are the rules of using Hess’s law to find enthalpy changes using equations?

A
  • If a substance appears in more than one equation ignore that substance
  • Never use the same equation twice
41
Q

What is meant by the term equilibrium?

A

The point in a reversible system where the rate of the forward reaction equals the rate of the backwards reaction

42
Q

What will happen to the concentration of both the products and the reactants in an equilibrium?

A

When equilibrium is reached the concentration of the products and the concentration of the reactants stops changing and the concentrations remain constant

43
Q

Why do we use the word dynamic to describe equilibriums?

A

Equilibriums are said to be dynamic as even when equilibrium is reached the reactions do not stop and both the forwards reaction and the backwards reaction will continue at the same rate

44
Q

What can be said about concentrations in an equilibrium?

A

Concentrations in an equilibrium are constant but not equal

45
Q

How does it impact the equilibrium if you start the reaction from the products side instead of the reactants side?

A

It does not matter if you start the reaction from products side or reactants side as the same position of equilibrium will be reached regardless

46
Q

What is meant by a closed system?

A

A closed system is a system where reactants and products cannot escape their container

47
Q

Why must a closed system be used for an equilibrium to occur?

A

As otherwise either the products or reactants will escape the system preventing the equilibrium from happening.

48
Q

What is meant by a reversible reaction?

A

A reaction where the reactants are converted to products and then the products are converted back into the reactants

49
Q

What is Le Chatelier’s principle?

A

Le Chatelier’s principle is that the position of an equilibrium in a chemical reaction will change to minimise the effect of any imposed change in the reaction conditions

50
Q

What does Le Chatelier’s principle say would happen if you increased the temperature of a chemical equilibrium

A

If temperature is increased then the equilibrium would attempt to minimise this imposed change by shifting to the endothermic side of the reaction to the endothermic side
(the endothermic side requires heat so the temperature decreases)

51
Q

What does Le Chatelier’s principle say would happen if you decreased the temperature of a chemical equilibrium?

A

If temperature is decreased the equilibrium would attempt to reduce this imposed change by shifting to the exothermic reaction
(Heat would be released increasing the temperature)

52
Q

What does Le Chatelier’s principle say would happen if you added a product or removed a reactant / increased the concentration of these things?

A

If concentration of the products increased or the concentration of the reactants decreased to reduce this imposed change the reaction would shift to the left (reactants side) this would reduce the concentration of the products and increase the concentration of the reactants

53
Q

What does Le Chatelier’s principle say would happen if you added a reactant or removed a product?

A

To minimise this imposed change the equilibrium would shift to the right side (products side)
This would increase the concentration of the products and decrease the concentration of the reactants

54
Q

What conditions must be met if changes in pressure are to effect an equilibrium?

A
  • The reaction must have at least one gaseous component
  • The number of moles on each side of the equation must be different for this to take place
55
Q

What does Le Chatelier’s principle say would happen if you increased the pressure of an equilibrium?

A

In order to reduce the imposed conditions the equilibrium would shift to the side with less moles of gas, this would have the effect of reducing the pressure

56
Q

What does Le Chatelier’s principle say would happen if you decreased the pressure of an equilibrium?

A

In order to reduce the imposed change the equilibrium would shift to the side which has more moles of gas, this would increase the pressure

57
Q

What impact does the use of a catalyst have on an equilibrium?

A

A catalyst has no effect on equilibrium as the catalyst increases the rate of both the forwards and backwards reactions, however catalysts will allow equilibrium to be reached more quickly

58
Q

Do catalysts impact the enthalpy change of equilibrium reactions?

A

No catalysts do not impact the enthalpy change in an equilibrium

59
Q

What is chromatography?

A

Chromatography is the separation of molecules based on the factors of
- Molecule size
- Molecule polarity

60
Q

What does the process of chromatography involve?

A
  • A mobile phase
  • A stationary phase
  • A retention factor value
61
Q

What is meant by a mobile phase?

A

The mobile phase in paper chromatography is the liquid solvent which dissolves the components of a mixture and carries them to the stationary phase

62
Q

What is meant by the stationary phase?

A

The stationary phase is the wet paper which the molecules are carried up through by the mobile phase. The stationary phase allows us to compare the retention factor values of the different molecules

63
Q

How do we calculate the retention factor value?

A

distance travelled by spot from the baseline / distance traveled by the solvent front from the baseline

64
Q

What does the y-axis of a gas liquid chromatography graph show?

A

Indicates the quantities of the substance in the mixture

65
Q

What is meant by the activated complex?

A

The activated complex is an unstable arrangement of atoms that forms at the maximum of the potential energy barrier

Higher Chemistry Prelim (3 decks)

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