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Stage 2 Chemistry > Topic 2 - Managing Chemical Processes > Flashcards

Topic 2 - Managing Chemical Processes Flashcards

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1
Q

What is a rate of reaction?

A

Rate of reactions refer to the rate at which chemical reactions occur over time. This can either be represented by the rate in which a product is formed or the rate in which a reactant is consumed.

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2
Q

How is rate of reaction measured?

A

The rate of reaction is measured using a concentration VS time graph. The gradient formula can be used to calculate average rate of reaction over an entire graph. Whereas, the gradient formula of a tangent at a specific point or differential calculus can be used to calculate the instantaneous rate of reaction at a specific point.

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3
Q

What does a steep slope mean in regards to rates of reaction?

A

A steep slope indicates a rapid rate of reaction.

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4
Q

What does a shallow slope mean in regards to rates of reaction?

A

A shallow slope indicates a slow rate of reaction.

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5
Q

What does zero slope mean in regards to rates of reaction?

A

Zero slope indicates no reaction occurring or the reaction has reached equilibria.

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6
Q

Does bond breaking require or release energy?

A

Bond breaking requires energy.

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7
Q

Does bond forming require or release energy?

A

Bond forming releases energy.

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8
Q

What occurs in relation to energy within all chemical reactions?

A

In all chemical reactions, there will be either a net release of energy into the surroundings or a net absorption of energy from the surroundings.

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9
Q

What happens to energy during an exothermic reaction?

A

Net release of heat energy to the surroundings, and the temperature of the surroundings increases.

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10
Q

What happens to energy during an endothermic reaction?

A

Net absorption of heat energy from the surroundings, and temperature of surroundings decreases.

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11
Q

Define enthalpy.

A

Enthalpy (H) is the total heat energy of the system at constant pressure and volume.

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12
Q

Define change in enthalpy.

A

The quantity of heat released when one mole of a substance reacts at a constant pressure.

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13
Q

Draw and explain an exothermic energy profile diagram.

A

Energy/heat is released. The energy of the reactants is greater than the energy of the products, as energy is emitted to surroundings. The change in enthalpy is negative.

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14
Q

Draw and explain an endothermic energy profile diagram.

A

Energy/heat is absorbed. The energy of the products is greater than the energy of the reactants, as energy is taken from the surroundings. The change in enthalpy is positive.

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15
Q

What does collision theory describe?

A

Collision theory is used to explain chemical reactions and the factors that affect the rate of the reaction. Reactants are particles that must collide with each other in order to react and form products.

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16
Q

What do successful collisions result in?

A

Product formation.

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17
Q

What do unsuccessful collisions result in?

A

No products formed and no chemical change.

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18
Q

What are the conditions for successful collisions?

A
  1. The reactant particles (molecules, atoms or ions) must collide.
  2. The colliding particles must have energy equal to or greater than the activation energy for the reaction.
  3. The reactant particles must collide in the correct orientation for a reaction to occur.
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19
Q

What is phrase used to describe the number of successful collisions per unit time?

A

The frequency of successful collisions.

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20
Q

What does the rate of reaction depend on?

A

The frequency of successful collisions.

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21
Q

What does a higher/lower frequency of successful collisions do to the reaction rate?

A

A higher frequency of successful collisions results in a quicker reaction rate. Whereas, a lower frequency of successful collisions results in a slower reaction rate.

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22
Q

What factors alter the rate of reaction?

A

Temperature, concentration, pressure, surface area, catalysis, and enzymes.

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23
Q

How does temperature impact rate of reaction?

A

The temperature of a substance is directly proportional to the average kinetic energy of the particles. This means that a higher temperature will result in faster particle movement due to a greater amount of kinetic energy. This increases the chances of molecules colliding with energy equal to or greater than the required activation energy. The frequency of successful collisions increases, thus increasing the rate of reaction.

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24
Q

How does concentration impact rate of reaction?

A

The higher the concentration, the more particles per unit volume. The closer particles are together, the more likely they are to collide. Thus, increasing the concentration of reactants, increases the frequency of successful collisions - causing a quicker rate of reaction.

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25
Q

How are pressure and volume related?

A

The pressure of a gas is inversely proportional to its volume.

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26
Q

How does pressure impact rate of reaction?

A

The pressure of a gas can be increased by decreasing the volume, allowing particles to collide more frequently. Specifically, decreasing the container size increases the gas pressure, which increases the probability of successful collisions and, indirectly, the frequency of successful collisions.

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27
Q

How does surface area impact rate of reaction?

A

Only the particles/atoms on the surface of a solid and able to collide with other reactant particles. Increasing the surface area of a reactant, increases the number of exposed particles which increases the frequency of successful collisions - quickening the rate of reaction.

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28
Q

How do catalysts impact rate of reaction?

A

Catalysts increase the rate of reaction by providing alternate energy pathways that lower the activation energy. They do so by increasing the proportion of reactants that possess energy equal to or greater than the required activation energy. Thus, catalysts increase the frequency of successful collisions, quickening the rate of reaction. Catalysts are not consumed during the reaction and remain chemically unchanged at the completion of the reaction (only small amounts are required).

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29
Q

What is the difference between homogenous and heterogenous catalysts?

A

Homogenous catalysts mean it have the same state (solid, liquid, gas) as the reactants.
Heterogenous catalysts have a different state to the reactants. Generally, homogenous catalysts function more effectively.

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30
Q

What are enzymes?

A

Enzymes are large protein molecules that act as biological catalysts. The catalytic ability of enzymes is linked to its unique 3D structure, in particular the shape of the active site where the reaction occurs.

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31
Q

How do enzymes impact rate of reaction?

A

Introducing an enzyme increases the proportion of reactants the possess energy equal to or greater than the required activation energy. This provides an alternate energy pathway that has lower activation energy, increasing the frequency of successful collisions and thus increasing the rate of reaction.

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32
Q

What distinguishes an irreversible reaction?

A

Irreversible reactions have a single directional arrow. The reactants collide to form products but the products cannot collide to form reactants. This means that only the “forward” reaction occurs.

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33
Q

What distinguishes a reversible reaction?

A

Reversible reactants have an equilibrium reaction, indicating that the reaction can go both directions. The reactants collide to form products, and the products can collide to form reactants. Both the “forward” and “backward” reactions can occur.

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34
Q

What is equilibrium?

A

When the rate of the forward reaction and the backward reaction are equal, the system is said to be at equilibrium.

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35
Q

What are the characteristic of equilibrium?

A

Equilibrium is a dynamic (moving) process, meaning the reaction has not stopped when it reaches equilibrium. It is just happening equally as fast in both directions. At equilibrium, there is no change in observed or measured properties such as colour, temperature, pH, pressure and concentration.

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36
Q

What are the conditions of equilibrium?

A

A system can only reach equilibrium if:
1. It is a closed system (reactants/products cannot be lost or gained to/from surroundings).
2. It is at constant pressure.

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37
Q

How is equilibrium tracked? What does this look like generally?

A

Equilibrium is tracked using rate VS time graphs. At the beginning of the reaction, once reactants are present. This means the rate of the forward reaction is greater than the rate of the backwards reaction. As the products form, the rate of the backward reaction increases. Thus, as more reactants are consumed, the rate of the forward reaction decreases. Eventually, the rate of the forward and backward reaction are equal and equilibrium has been reached.

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38
Q

What does a higher molar ratio of reactants do to equilibrium graphs?

A

The distance between the initial and equilibrium point is increased with the molar ratio. Stoichiometric ratios can be used to predict these equilibrium curves.

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39
Q

What happens to the equilibrium graph if the molar ratio of reactants to products is 1:2 (A <–> 2B)?

A

The decrease of concentration of the reactants will be half of the concentration curve or the products.

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40
Q

What is the general equation for the equilibrium constant?

A

Kc = [C]^c[D]^d/[A]^a[B]^b for the equation aA + bB <–> cC + dD
where [A], [B], [C] and [D] are concentrations of species A, B, C and D at equilibrium

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41
Q

What does the equilibrium constant describe?

A

The equilibrium constant describes the position of equilibrium (whether the reactants or products are favoured).

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42
Q

What are the conditions and units of Kc?

A

Kc has no units (it is a ratio of concentrations). Kc has a constant value at a constant temperature and pressure (for the same reaction).

43
Q

What does the magnitude of the equilibrium constant indicate?

A

The magnitude of the equilibrium constant provides an indication on how far the reaction has proceeded at equilibrium and the yield of products relative to the quantities of reactants at equilibrium.

44
Q

What does a higher Kc indicate in terms of yield and which reaction is favoured?

A

With a higher Kc, higher yields of products at equilibrium occur and the forwards reaction has proceeded to a larger extent at equilibrium.

45
Q

What does a smaller Kc indicate in terms of yield and which reaction is favoured?

A

With a smaller Kc, lower yields of products at equilibrium occur and the forward reaction has proceeded to a smaller extent at equilibrium.

46
Q

What happens when the Kc>1?

A

The equilibrium lies to the right and the forward reaction is favoured. The concentration of products is greater than the concentration of reactants.

47
Q

What happens when 0<Kc<1?

A

The equilibrium lies to the left and the backward reaction is favoured. The concentration of reactants is greater than the concentration of products.

48
Q

What is Henry Louis Le Chatelier’s principle?

A

“When a system at equilibrium is subjected to a change in concentration, temperature, volume or pressure, then the system readjusts itself to (partially) counteract the effect of the applied change and a new equilibrium is established.”

49
Q

What the correct way to start Le Chatelier’s questions?

A

According to Le Chatelier’s Principle, when stress is placed on a system at equilibrium, the equilibrium will shift in direction to counteract the stress.

50
Q

How does the stress of concentration impact equilibrium (Le Chatelier’s principle)?

A

If the concentration of a reactant or product is increased or decreased when the system is at equilibrium the system will counteract change by shifting equilibrium position.

51
Q

What happens if reactant concentration increases?

A

Systems will shift to consume the reactants and the equilibrium will shift to the right.

52
Q

What happens if product concentration is increases?

A

Systems will shift to consume the added product and the equilibrium shifts to the left.

53
Q

How does the stress of pressure impact equilibrium (Le Chatelier’s principle)?

A

The pressure of a system is altered by changing the volume of the reaction vessel. Thus, if the pressure of the system is increased or decreased when the system is at equilibrium, the system will move to counteract the change by shifting equilibrium position.

54
Q

What is pressure inversely proportional to?

A

Pressure and volume are inversely proportional.

55
Q

How does an increase in pressure impact the position of equilibrium?

A

According to Le Chatelier’s principle… BLAH BLAH BLAH. Increasing pressure reduces the volume of the reaction vessel. This means that the side consisting of less moles of gaseous particles will be favoured. Thus, the equilibrium will favour the … direction.

56
Q

How does the stress of temperature impact equilibrium (Le Chatelier’s principle)?

A

Within equilibrium reactions, the reverse (backward) reaction is thermodynamically opposite to the forward reaction. If the forward reaction is endothermic, the backward reaction is exothermic. If the temperature of the reaction is increased or decreased, the equilibrium will shift to help oppose this change.

57
Q

What happens to equilibrium if temperature of the reaction is increased?

A

If the temperature is increased, the endothermic reaction is favoured to decrease the temperature.

58
Q

What happens to equilibrium if temperature of the reaction is decreased?

A

If the temperature is decreased, the exothermic reaction is favoured to increase the temperature.

59
Q

How does adding a catalyst impact equilibrium?

A

Adding a catalyst to a reaction will not change the position of equilibrium (Kc), only the speed at which the system reaches equilibrium.

60
Q

What impacts the stresses on Kc?

A

Only a change in temperature will impact the Kc. Concentration, pressure and catalyst will not impact Kc values.

61
Q

What is ion exchange chromatography?

A

Ion exchange chromatography is used to separate ions. A glass cylindrical column is packed with resin that either has a positive or negative charge. If the resin is positively charged, it attracts anions. If resin is negatively charged, it attracts cations.

62
Q

How can the conditions of ion exchange chromatography be manipulated by changing pH?

A

If the pH of the mobile phase is changed, the molecule may change from neutral or charged. The affinity to the charged resin will change.

63
Q

What equation can be used to describe ion exchange chromatography?

A

X-(resin) + Y-(aq) <–> Y-(resin) + X-(aq)

64
Q

How can the conditions of ion exchange chromatography be manipulated by changing concentration?

A

According to Le Chatelier’s principle… BLAH BLAH. If the concentration of ion Y in solution is increased, the equilibrium shifts in the forward direction.

65
Q

How does column chromatography work?

A

During column equilibrium, one specific anion/cation is adhered to the resin. An analyte sample is added and displaces the ions adhered to the resin. To get the sample to desorb, the column is flushed with the original ion aqueous solution, displaying the analyte ions.

66
Q

What are the conditions of ion exchange chromatography?

A

Use: Separation of Ions/Charged Particles
Stationary Phase: Resin (+ or -) Packed into a Column
Mobile Phase: Solvent Moving with Gravity

67
Q

What is hard water and how does it impact society?

A

Hard water is essentially any water with a high concentration of calcium or magnesium cations. This can lead to mineral build up, prompting problems with washing clothes, skin irritations and brittle hair.

68
Q

What are zeolites?

A

Zeolites are hydrated aluminosilicates composed of SiO4 and AlO4, tetrahedral symmetrically stacked together to create open porous honeycomb-like structures.

69
Q

What are the advantages of zeolites?

A

Zeolites are extremely customisable meaning they can by synthesised to have pores, tunnels and cavities of precise size to maximise surface area.

70
Q

How is soap used to remove grease?

A

Soap consists of a negatively charged, hydrophilic head and a non-polar, hydrophobic tail. The hydrophobic tail dissolves in the non-polar grease and hydrophilic head dissolves in the water. This agitation separates grease from the surface, forming micelles that repel (negative VS negative charge). This prevents grease from forming a large mass, enabling it to be removed.

71
Q

How does hard water interfere with soap removal?

A

SAME PROCESS AS REGULAR REMOVAL. However, the positive calcium ions within the hard water bind to the negatively charged micelle. This prevents the micelles from being formed, meaning the grease cannot be removed properly and the soap is ineffective.

72
Q

What is the charge of the pores within zeolites and how do they impact the efficiency?

A

The pores in zeolites are negatively charged, thus they hold cations through electrostatic attractions. Water can be passed through a zeolite and the cations in the water will displace the cations in the pores.

73
Q

How can zeolites be used to treat hard water (equation)?

A

Zeolites are used as water “softeners” to remove Ca2+ and Mg2+ ions from water.
Mg2+(water) + Na+(zeolite) <–> Mg2+(zeolite) + Na+(water)
Hard water is passed through zeolite containing Na+ ions in the pores. The Ca2+ and Mg2+ ions replace the Na+ ions in the zeolite pores as they are more highly charged and therefore have a stronger attraction to the negatively charged zeolite surface. Equilibrium is pushed in the forward direction.

74
Q

How are zeolites regenerated?

A

Zeolite, now containing Ca2+ and Mg2+ ions in its pores can be regenerated for future use once all the negative sites on the surface of the zeolite are occupied with cations from hard water by flushing with a high concentration of Na+ ions, forcing the equilibrium back to the left.

75
Q

What is chlorination of water used for?

A

Chlorination of water kills bacteria by forming oxidising agents, disinfecting the water to make it suitable for household use.

76
Q

How does water chlorination work (equation)?

A

Hypochlorous acid is a weak acid and partially ionises in solution, producing the hydochlorite ion:
HOCl(aq) + H2O(l) <–> H3O+(aq) + OCl-(aq)
Chlorine, hypochlorous acid and the hypochlorite ions are all oxidising agents that can kill bacteria. They are all reduced to the chloride ion, Cl-, as they kill bacteria.

77
Q

Why is hypochlorous the most effective at killing bacteria?

A
  • it is small (H and O atoms are smaller than a Cl atom)
  • has no charge allowing it to penetrate the non-polar walls of bacteria and oxidise proteins
78
Q

Why is chlorine gas not used to treat water? What is used instead (equation)?

A

Chlorine gas is not used to treat water as it is a corrosive and highly toxic gas. Hypochlorite salt, such as NaOCl or Cal(ClO)2, is used to chlorinate water. When combined with water, it establishes the following equilibrium equation to form hypochlorous acid:
OCl-(aq) + H2O(l) <–> HOCl(aq) + OH-(aq)

79
Q

What are silicates?

A

Silicon is the most abundant element in the Earth’s crust. Not found in elemental state, yet in its oxidised form (SiO2) commonly referred to as silica, silicates and aluminosilicates.

80
Q

What are all silicates composed of?

A

All silicate materials are composed of SiO4^4- tetradhedral units. These can exist either on their own or as complex polymetric structures; forming chains, rings or three-dimensional networks. The SiO4 tetrahedral join through single O-Si-O bonds, meaning they will always have 4 bonds. It is the stacking that gives them their shape.

81
Q

What are aluminosilicates and how does this impact the charge of the structure?

A

Aluminosilicates are silicates with some Si atoms being replaced with Al atoms. Each time an Si atom is substituted for an Al atom, the overall charge decreases by one (Si^4+ and Al^3+).

82
Q

How is the negative charge on silicates and aluminosilicates counteracted?

A

This negative charge is counteracted with a metal cation, forming a neutral silicate and aluminosilicate mineral. Other anions may also be present in the mineral, such as hydroxide and fluorides, as well as water.

83
Q

How is a silicate/aluminosilicate formula constructed?

A

Use the overall neutral charge of the ion, and charges/oxidation numbers of individual atoms, to determine the charge on the silicate.

84
Q

What are the relevant oxidation numbers of silicon, oxygen and aluminium?

A

Silicon +4
Oxygen -2
Aluminum +3

85
Q

Why are clays important in terms of silicates/aluminosilicates?

A

Plants would be unable to survive without clays, meaning humans would also be dead. Clays consist of silicates or aluminosilicates with particle size of 2x10^-6m, formed from the weathering and decomposition of rocks that contain silicates. They are involved in the absorption, retainment and transfer of nutrients (cations).

86
Q

What is the structure of clay?

A

Clays are made up of parallel sheets of silicates and/or aluminosilicates. The surface of the sheets contain hydrated hydroxyl functional groups.

86
Q

How does cation exchange function within clay?

A

The overall negative charge on the surface of the silicate/aluminosilicate sheet allows cations to absorb onto the surface via electrostatic attractions. The net charge of the clay surface must be constant, meaning the cations absorbed onto the clay surface must exchange with cations present in the soil solution. This process is called cation-exchange, and it is equilibrium based so there is a continual exchange of cations between clay and water.

87
Q

What does soil solution refer to?

A

The water within the soil.

88
Q

What happens to equilibrium within cation-exchange in the soil solution and why?

A

When plants assimilate ions (take up ions via roots), more cations are released from the clay into water to be made available. This shifts the position of equilibrium in the forward direction.

89
Q

What is the general equation for cation-exchange within soil?

A

X+(aq) + Y+(clay) <–> X+(clay) + Y+(aq)

90
Q

What is soil acidity a measure of?

A

Soil acidity (or pH) is a measure of the concentration of hydrogen ions in the soil.

91
Q

How do soils become acidic?

A

Most soils are naturally acidic, dur to the hydrogen ions present in the soil from rain water and the use of ammonium-based fertilisers. Plants also pump hydrogen ions out of their roots and into the soil solution to encourage the release of nutrients from clay particles.

92
Q

How does soil acidity impact society?

A

High soil acidity (low pH) affects the rate of plant growth, the cation-exchange process and the functionality of bacteria within the soil.

93
Q

How would acid rain affect cation-exchange?

A

Acid rain causes an increase in soil acidity (H+ in water). These ions are attracted to the negatively charged clay surface and displace the cations currently absorbed to the clay. This shifts equilibrium in the forward direction meaning metal cations are released for uptake by plants.

94
Q

What does soil salinity measure?

A

Soil salinity is a measure of the concentration of soluble salts e.g. Na+, Cl-, Ca2+, and Mg2+ in the soil.

95
Q

How does soil salinity occur?

A

Salt are present in the soil due to the weathering of rocks that contain silicates and aluminosilicates.

96
Q

How may soil salinity impact the environment?

A

Although plants require many cations as nutrients, a high concentration may have negative effects on plants. The concentration of salts in the soil may become high if the soil does not have drainage or if there has been limited rainfall. Sodium ions replace larger metal ions, decreasing the strength and tension of the soil to form cracks within the soil.

97
Q

Within industrial processes, what are raw materials, waste products and by-products?

A

Raw materials: Unprocessed substances converted by chemical or physical means into useful products or energy (coal, oil, natural gas, hydrocarbons, air, water, salt, metal ores and minerals.
Waste products: Undesirable substances produced from the chemical process that have no commercial value, cannot be reused//recycled, and cannot be used in other chemical processes to generate energy. Must be disposed of via either landfill, dumping into the ocean or emitting into atmosphere.
By-products: Substances produced from the chemical process that are not the desired end products but have commercial value, can be reused/recycled or can be used in another chemical industrial process to generate energy

98
Q

What is yield?

A

The yield is the quantity (how much) of the product was obtained from a chemical process. It is a measure of the efficiency of a chemical process.

99
Q

What is the calculation used to find percentage yield?

A

% yield = (actual yield/theoretical yield) X100

THEORETICAL YIELD - dependent on limiting reagent

100
Q

Why is moderately low pressure and temperature used in industrial applications, despite affecting the optimisation of chemical processes?

A

A moderate temperature is a tradeoff between yield and rate of reaction. An increased time to carry out the reaction, due to a slower reaction rate, will increase operating costs.

Atmospheric pressure is a tradeoff between yield and cost. Generating high pressures is both expensive and unsafe.

Catalyst may be used to increase the rate of reactions, however, they can also be expensive.

101
Q

How can the Haber process (exothermic) be optimised?

A

According to LeChatliers Principle, when stress is put on a system at equilibrium, the equilibrium shifts to counteract the stress. To optimise the Haber process, lower temperatures will cause the exothermic reaction (forwards) to be favoured – increasing the yield of ammonia. However, according to collision theory, lowering the temperature will decrease the frequency of collisions – causing reduced kinetic energy to be present and potentially not enough energy to overcome the activation energy, meaning limited rate of reaction. A catalyst could be used to increase the rate of reaction. Increased pressure would also cause the forwards reaction to be favoured as there are more moles of reactants present than moles of products. However, increasing pressure requires a substantial amount of energy and, thus, cost. Therefore, the reaction should be done at moderately high temperatures, with a catalyst and at atmospheric pressure, to optimise the yield and limit cost. The product could also be removed throughout production to increase yield.

102
Q

What are some methods to reduce energy costs within industrial chemical processes?

A
  • using heat energy (feedback into process or convert)
  • operating at a lower temperature (e.g. use a catalyst instead)
  • running process continuously (starting and stopping requires more energy)
103
Q

What do ICE tables represent?

A

Initial presence of substances (reactants are given, products will be zero). Change in moles, based on molar ratios within the equation. Presence at equilibrium.

Stage 2 Chemistry (4 decks)

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