Managing Chemical Processes Flashcards
(108 cards)
1
Q
What is a rate of reaction?
A
The rate at which the chemical reaction occurs overtime. This can be expressed as either the rate at which a product is formed, or the rate at in which a reactant is consumed.
2
Q
How is the rate of reaction measured?
A
Through a concentration vs time graph.
3
Q
How is the average rate of change calculated?
A
Using the highest and lowest point on the function.
4
Q
How is the instantaneous rate of change calculated?
A
By drawing a tangent to that point, and using the intercepts (x and y) of that tangent.
5
Q
What does the slope of the reaction tell us?
A
It provides the information on the speed of the rate of the reaction.
Steep slope - rapid rate of change
Shallow slope - slow rate of reaction
Zero slope - no reaction occurring or the reaction has reached equilibrium.
6
Q
What do all chemical reactions entail?
A
The breaking then making of bonds.
7
Q
What does breaking of bonds do?
A
Uses energy (endothermic)
8
Q
What does the forming of bonds do?
A
Releases energy (exothermic)
9
Q
What happens in an exothermic reaction?
A
Net release of heat energy to the surroundings.
Temperature of the surroundings increases.
e.g: combustion, respiration, acid-base neutrilisations.
10
Q
What happens in an endothermic reaction?
A
Net absorbance of heat energy from the surroundings.
Temperature of the surroundings decreases.
e.g: photosynthesis, melting and evaporation.
11
Q
What is Enthalpy (H)?
A
It is the total energy/heat of the system at at constant pressure and volume.
12
Q
Draw exothermic and endothermic energy profile diagrams
A
13
Q
What is the collision theory used to explain?
A
Collision theory is used to explain chemical reaction and the factors that affect the rate of reactions. The reactants are particles that must collide with each other in order to react and form products.
14
Q
What do successful collisions result in?
A
Product formation. The kinetic energy of the colliding particles exceeds the activation energy for the reaction.
15
Q
What do unsuccessful collisions result in?
A
No products formed and no chemical change. The kinetic energy of the colliding particles does not exceed the activation energy for the reaction leading to the particles bouncing off one another.
16
Q
For a successful collision what three criteria must be met?
A
The reactant particles must collide.
The colliding particles must have energy equal or more than the activation energy.
The reactant particles must collide in the correct orientation for a reaction to occur.
17
Q
What does the rate of reaction depend on?
A
The frequency of successful collisions.
High frequency of successful collisions - Rapid reaction rate
Smaller frequency of successful collisions - Slow reaction rate
18
Q
What factors can alter the conditions in which the particles collide in?
A
Temperature
Concentration
Pressure
Surface Area
Catalysis
Enzymes
19
Q
How does the temperature of a reaction impact the rate of reaction?
A
The temperature of a substance is the average kinetic energy of particles in the substance.
The higher the temperature, the particles move faster due to the greater amount of kinetic energy.
This increases the chances of a molecule colliding with energy equal to or greater than the activation energy.
The frequency of successful collisions increases, thus increasing the rate of reaction.
20
Q
How does concentration impact the rate of reaction?
A
The higher the concentration, the more particles per unit volume.
The closer particles are and more likely they are to collide.
Increasing the concentration of the reactants, increases the frequency of successful collisions.
21
Q
What impact does pressure have on the rate of reaction?
A
Pressure of a gas can be increased by decreasing the volume, allowing particles to collide more frequently.
Decreasing the container size, increases the gas pressure, which increases the probability of successful collisions and indirectly, the frequency of successful collisions/
22
Q
What impact does surface area have on the rate of reaction?
A
It increases the rate of reaction as only the particles on the surface of a solid are able to collide with other reactant particles.
Increases the surface area of a reactant, increase the number of surface/exposed particles which increase the frequency of successful collisions.
23
Q
What impact do catalysts have on the rate of reaction?
A
Catalysts increase the rate of reaction by providing alternate energy pathways that lower activation energy.
Introducing a catalyst increases the proportion of reactants that possess energy equal to or greater than the activation energy. This increases the frequency of successful collisions.
Catalysts are not consumed during the reaction and remain unchanged at the completion of the reaction - requiring only small amounts.
Homogenous catalysts - same state (solid, liquid or gas).
Heterogeneous catalyst - different states.
24
Q
What impact do enzymes have on the rate of reaction?
A
Enzymes are large protein molecules that act as biological catalysts. The catalytic ability of enzyme is linked to its unique 3D structure, in particular the shape/structure of the active site where the reaction occurs. It constrain the molecule to certain molecules. This lowers the activation energy, increasing the frequency of successful collisions.
25
Describe the conditions of an irreversible reaction
- Reactants collide to form products.
- Products cannot collide to form reactants
- Only the 'forward' reaction occurs
- This is the typical reaction
26
Describe the conditions of an reversible reaction
- Reactants collide to form products.
- Products collide to form reactants.
- Both the 'forward' and 'backwards' reactions occurs.
This is an equilibrium balancing act.
27
What is equilibrium?
When the rate of a forward reaction and backward reaction are equal, the system is said to be at equilibrium.
- Equilibrium is a dynamic (moving) process. The reaction has not stopped, it is just happening equality as fast in both directions.
- At equilibrium there is no in observed or measured properties such as colour, temperature, pH, pressure or concentration.
- The concentration remains the same.
Equilibrium is when the products and reactants are being consumed and formed at the same rate. NOT MOLAR RATIO!
28
Describe the conditions of equilibrium
It is a system (reaction) can only reach equilibrium.
- It is a closed reaction (reactants and products cannot be lost or gained to/form surroundings).
- Its at a constant pressure.
If these conditions are not met, the forward (right) or the backward (left) reaction will be favoured.
We can force equilibrium to favour a forward or backwards reaction.
29
What is an equilibrium constants?
The position of equilibrium (whether the reactants or products are favoured) can be described using the equilibrium constant (Kc).
The magnitude of the equilibrium constant provides an indication on how far the reaction has proceeded at equilibrium and the yield (amount) of products relative to the quantities of reactants at equilibrium.
29
How to track equilibrium?
At the start of the reaction only reactants are present.
The rate of the forward reaction is greater than the rate of the backward reaction.
As product forms the rate of the backward reaction increases.
As more reactants are consumed the rate of the forward reaction decreases.
Eventually the rate of the forward and backward reactions are equal.
When at a straight line the system has reached equilibrium.
30
What is the formula for equilibrium constants?
aA + bB <-> cC + dD
Kc = [C]^c[D]^d/[A]^a[B]^b
Kc = [product]^ coefficient value/[Reactants]^ coefficient
[A], [B], [C] and [D] are concentrations of the species A, B, C and D at equilibrium.
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).
31
What does it meant by a higher Kc value?
- Higher yield of products at equilibrium.
- Forward reaction has proceeded to a large extent (reactants -> products) at equilibrium.
32
What is meant by a lower Kc value?
- Lower yields of products at equilibrium.
- Forward reaction has proceeded to a smaller extent (reactants -> products) at equilibrium.
33
If Kc > 1 what does this mean?
- The equilibrium lies to the right and the forward reaction is favoured.
- Concentration of products greater than concentration of reactants.
34
If Kc < 1 what does this mean?
- The equilibrium lies to the left and the backward reaction is favoured.
- Concentration of reactants greater than concentration of products.
35
How to spell LCP
Le chatelier with a hat on the a
36
What is le chateliers principle?
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 charge and a new equilibrium is established.”
It predicts how a stress on a system at equilibrium affects the positions of equilibrium.
The system always opposes the stress by shifting the position.
The system opposes the stress except with volume it accepts it.
37
Describe concentration as a stress
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.
38
What happens if we increase reactant concentration?
System will work to consume reactant, shift equilibrium to the right.
39
What happens if we decrease reactant concentration?
System will want to produce more product, equilibrium shifts to the left.
40
Increase in the reactant concentration...
System response - consume the added reactant
Equilibrium position - equilibrium shifts to the right.
41
Decrease in the reactant concentration...
System response - produce more of the removed reactant.
Equilibrium position - Equilibrium shifts to the left
42
Increase in the product concentration...
System response - consume the added product
Equilibrium position - equilibrium shift to the left
43
Decrease in the product concentration...
System response - produce move of the removed product
Equilibrium position - equilibrium shifts to the right
44
Example answer for le chateliers principle
· Increasing the concentration of the reactant places a stress on the system.
· According to Le Châtelier’s Principle states that the system will move in the direction to counteract the change by reducing the concentration of reactants by shifting the position of equilibrium to the right.
· The concentration of products will increase.
45
Describe the temperature with equilibrium
Within equilibrium reaction, the reverse 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.
If temp is increased is increased, endothermic reaction is favoured.
If temp is decreased, exothermic reaction is favoured.
46
Increase in the pressure (by decreasing volume)
System response - shifts to reduce the pressure by producing fewer moles of gaseous particles (occupy less volume).
Equilibrium Position - Equilibrium shifts to the side with the fewer number of moles of gaseous particles.
47
Decrease in the pressure (by increasing the volume)
System response - Shifts to increase the pressure by producing more moles of gaseous particles (occupy more volume).
Equilibrium position - equilibrium shifts to the side with the greater number of moles of gaseous particles.
48
Increase in temperature...
System response - shift to decrease the temperature.
Equilibrium position - equilibrium shifts in the endothermic direction.
49
Decrease in the temperature...
System Response - shifts to increase the temperature.
Equilibrium position - equilibrium shifts in the exothermic direction
50
Describe the effect on a Kc value when a catalyst is added...
Adding a catalyst to a reaction will not change the position of equilibrium (Kc), only the speed at which the system reaches equilibrium. It lowers the activation energy, providing an alternate energy pathway with less activation energy. Adding the catalyst will not change the position of equilibrium, it will change the speed at which the reaction will react equilibrium.
51
Describe the effect of increase in temperature on equilibrium...
Effect on equilibrium - shifts in the direction of the endothermic reaction
Ration of reactants to products - In the endothermic direction; [reactant] decreases, [product] increases.
Effect on Kc - change
52
Effect of decrease in concentration of products on equilibrium...
Effect on equilibrium - shift in the direction to increase [products]
Ration of reactants and products - no change
Effect on Kc - no change
53
Effect of increase in pressure on equilibrium...
Effect on equilibrium - shifts in the direction of the fewer moles of gas
Ration of reactants and products - no change
Effect on Kc - no change
54
Effect of addition of a catalyst on equilibrium...
Effect on equilibrium - reaches equilibrium faster
Ratio of reactants and products - no change
Effect on Kc - no change
55
What is ion exchange chromatography used?
To separate positively and negatively charged ions, often known as zwitterions.
56
Describe the process of ion exchange chromatography...
A glass cylindrical column is pack with resin that is either positively or negatively charged. During the column equilibrium, one specific anion/cation is adhered to the resin.
Analyte sample is added and displaces the ion adhered to the resin.
To get the sample to desorb column is flushed with original ion aqueous solution, displacing analyte ions.
57
If the resin of ion exchange chromatography is positively charged what does it attract?
Anions, releasing cations. - anionic exchange
58
If the resin of ion exchange chromatography is negatively charged what ions will it attract?
Cations - cation exchange
59
What are the two conditions of ion exchange chromatography that can be manipulated?
Changing pH
Changing concentration
60
Describe the process of changing pH to manipulate ion exchange chromatography...
Manipulating pH can change the charge of the ion.
61
Describe the process of manipulating concentration to alter the conditions of the ion exchange chromatography...
X_ (resin) + Y- (aq) <-> Y- (resin) + X- (aq)
The position of equilibrium can be shift form one side to the other.
If the concentration of ion Y in solution is increased the equilibrium shifts in the forward direction.
If at equilibrium, this can be altered using stresses like concentration.
62
Describe the benefits, disadvantage, stationary phase and mobile of TLC...
Use - quick, cheap, fast
Disadvantage - cannot get substance off of the the plate after use.
Stationary phase - solid adsorbed on the surface of the pale.
Mobile phase - Solvent moving due to capillary action.
63
Describe the benefits, stationary phase and mobile of Column chromatography...
Use - Allows separated components to be collected and analysed.
Stationary phase - solid adsorbent packed into the column.
Mobile phase - solvent moving with gravity.
64
Describe the benefits, disadvantage, stationary phase and mobile of GSC...
Use - for volatile substances
Disadvantage - once in the gas form it cannot form a solid or liquid.
Stationary phase - solid adsorbent on the inner surface or filling the coil.
Mobile phase - carrier gas
65
Describe the benefits, stationary phase and mobile of HPLC...
Use - for substances
Stationary phase - solid adsorbent on the inner surface or filling the coil.
Mobile phase - liquid (eluent) pumped under pressure
66
Describe the benefits, disadvantage, stationary phase and mobile of ion exchange...
Use - ions/charged particles
Disadvantage - only works for ions
Stationary phase - Resin (+ or -) packed into a column
Mobile phase - solvent moving with gravity
67
What is hard water?
Hard water is essentially any water with a high concentration of calcium or magnesium cations.
This can lead to mineral build up, problems with washing clothes, skin irritations and brittle hair.
Houses use water softeners to counteract this.
68
What is a zeolite?
Zeolites are hydrated aluminosilicates composed of SiO4 and AIO4 tetrahedral symmetrically stacked together to create open porous honeycomb-like structures.
A variety of zeolites can be synthesised to have pores, tunnels and cavities of precise size, all with vast surface area, providing vast surface area for interactions between the solvent and the surface of the zeolite material.
The pores in zeolites are negatively charged, thus they hold cations through electrostatic interactions.
Water can be passed through a zeolite and the cations in the pores may be exchanged for cations in the water (this is ion exchange).
69
What are the advantages of zeolites?
They're customisable and can be made to capture ions of interest.
They can be made very big and therefore operate on a large scale.
70
Describe the role of zeolites in ion exchange...
Zeolites can be used as water 'softeners' to remove the Ca2+ and Mg2+ ions from water.
Mg2+(water) + Na+(zeolite) <-> Mg2+(zeolite) + Na+(water)
Hard water(contains calcium or magnesium ions), is passed through zeolite containing Na2+ ions in the pores.
The Ca2+ and Mg2+ ions replace Na2+ 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.
Through this, zeolite, 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.
71
What is chlorination of water?
Water must be treated before being suitable for drinking, for household used or in swimming pools. This removes bacteria and ensures an acceptable odour, colour and taste.
Disease killing bacteria are killed by chemical treatment with an oxidising agent such as chlorine gas (Cl2), or hypochlorite ions, (OCl-).
72
Describe the process of chlorinating water...
When Cl2 has is added to water, the equilibrium of the below equation is established.
Cl2(g) + 2H2O(l) <-> HOCl(aq) + H3O+(aq) + Cl-
Adding a base removes the H3O+ ions and shifts the equilibrium to the right, increasing the concentration of the hypochlorous acid, HOCl, and lowering the concentration (due to Le Chatiler's principle.
This is done because the back reaction is favoured producing the harmful HOCl.
73
Describe how HOCl ionises in water...
Hypochlorous acid is a weak acid so it partially ionises in solution producing the hypochlorite ion -
HOCl(aq) + H2O(l) <-> H3O+(aq) + OCl-(aq)
Chlorine (Cl2), hypochrolous acid (HOCl) and the hypochlorite ion (OCl-) are all oxidising agents that can kill bacteria. They are all reduced to the chlorine ion (Cl-), as they oxidise (kill) bacteria.
74
What is the most effective oxidising agent?
Hypochlorous acid (HOCl), is the most effective at killing bacteria.
It is small (H and O atoms are smaller than a Cl atom).
It has no charge allowing it to penetrate the non-polar walls of bacteria and oxidise proteins.
75
What and how are salts added to water to chlorinate it?
NaOCl or Ca(ClO)2
When added to the water, the hypochlorite ion establishes the following equilibrium with hypochlorous acid -
OCl-(aq) + H2O(l) <-> HOCl(aq) + OH-(aq)
76
What is a silicate?
Silicon is the most abundant element in the Earth's crust. It is not found in elemental state, yet in its oxidised form (SiO2) commonly referred to a silica, silicates and alumosilicates.
77
What are all silicate materials composed of?
SiO4^4- tetrahedral units. These can exist either on their own or as complex polymetric structures; forming chains, rings or three-dimensional networks.
The SiO4 tetrahedra join through O - Si - O bonds.
78
What is an aluminosilicate?
silicates which some Si atoms have been replaced with Al atoms. This commonly occurs in 3D networks and sheet silicates.
Each time an Si atom is substituted for an Al atom, the overall charge decreases by one (negative charge increases by one).
Silicon ion Si4+, has a higher positive charge than the aluminium ion Al3+.
Negative charge on silicates and aluminosilicates must be counteracted with a metal cation.
Forms a neutral silicate or aluminosilicate mineral. Other anions such as hydroxide and fluorides may be present in the mineral as well as water.
79
What are the two different methods for constructing a silicate/aluminosilicate?
1. formula of a mineral (silicate or alumina silicates with metal ions) known
2. Formula of mineral not known
80
Describe the first method of constructing a silicate/aluminosilicate...
Formula of mineral (silicate or alumina silicate with metal ions) known
The formula of a silicate anion or aluminosilicate anion can be deduced from the formula of the silicate or aluminosilicate mineral.
1. The overall charge of the mineral is zero. (The charges on the metal cations balance the charge on the silicate/aluminosilicate anion).
2. Determine the total charges of the metal cations and anions other than the silicate/aluminosilicate present in the mineral.
3. Determine the charge on the silicate/aluminosilicate required to have a neutral charge in the mineral.
81
Describe the second method of constructing a silicate/aluminosilicate...
Formula of mineral not known
The formula of a silicate anion or aluminosilicate anion can also be determined using oxidation numbers.
1. Determine the total oxidation number of the Si atoms.
2. Determine the total oxidation number of the O atoms.
3. (Determine the total oxidation number of the Al atoms - if an aluminosilicate anion).
4. The sum of these oxidation numbers is the charge on the silicates (or aluminosilicates).
82
What are the oxidation numbers of silicon, oxygen and aluminium?
+4, -2, +3
83
What are clays?
Clays consist of silicates or aluminosilicates with particles size than 2 ppb, formed from the weathering and decomposition of rocks and containing silicates.
Clays are the most important constituents of solid because they are involved in the absorption, retainment and transfer of nutrients (cations).
Clays are made up of parallel sheet of silicates and/or aluminosilicates. The surface of the sheets contain hydrated hydroxyl function groups.
84
Describe the process of cation exchange in clays...
The overall negative charge of the surface of the silicates/aluminosilicate sheets allows cation to adsorb onto the surface via electrostatic attractions.
Cations adsorb onto the clay surface can be exchanged with cations present in the soil solution in a process called cation-exchange.
Equilibrium based process - there is a continual exchange of cations between clay and water.
85
What needs to be maintained for clay cation exchange?
the surface net charge
86
Describe the process of plants assimilating ions...
When plants assimilate ions, more cations are released from the clay into water to be made available.
This can be though shifting the position of equilibrium to the forward direction.
87
What is soil acidity measuring?
Soil acidity (or pH) is a measure of the concentration of hydrogen ions within the soil.
88
Describe the disadvantages of soil acidity...
High soil acidity, low pH effect the rate of plant growth, the cation exchange process and the action of bacteria in the soil.
89
How does acid rain impact soil acidity?
Acid rain causes an increase in soil acidity, these ions are attracted to the negatively charged clay surface and displace the cations currently adsorbed to the clay.
H+(aq) + Ca2+(clay) <-> H+(clay) + Ca2+(aq)
The equilibrium is shifted to the right:
- Benefits are metal cations are released for uptake by plants
- If there is an increase in rain fall, cations will be washed away removing nutrients - plants then die
- If aluminium ions are released plant life dies due to toxicity.
90
What is soil salinity?
Soil salinity is a measure of the concentration of soluble salts, e.g Na+, Cl-, Ca2+, and Mg2+ in the soil.
Salts are present in the soil due to the weathering of rocks containing minerals e.g silicates and aluminosilicates.
Although plants require many cations as nutrients, a high concentration of soluble salts can have negative impacts on plants.
The concentration of salts in the soil may become high if the soil does not have adequate drainage or if there has been limited rainfall.
High soil salinity effects water and therefore nutrient uptake by plant (via osmosis).
91
What three general types of material generated in chemical industry?
- Basic chemicals (petroleum, polymers and fertilisers)
- Consumer products (soap, surfactants and cosmetics)
- Specialty chemicals (paper, paints inks and pesticides)
92
What are flow charts used for?
To detail chemical processes.
93
What is a raw material?
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).
94
What is a waste product?
It is an undesirable substance 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.
95
What is a by-product?
Substances produced from the chemical process that are not desired end products but have commercial value, can be reused/recycled or can be used in another chemical industrial process to generate energy.
96
What is yield?
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.
% yield = (actual yield/theoretical yield) x 100
97
What is actual yield?
The quantity of product made.
98
What is theoretical yield?
The quantity of the product expected (assuming all limiting reagents are converted).
99
What makes a chemical process ideal for yield?
Reactions that provide the most yield in the shortest amount of time.
100
Describe the relationship between low pressure and temperature?
Moderate temp is a trade off between yield and rate of reaction.
Low rate of reaction increases time required to carry out the reaction, increasing operating costs.
Atmospheric pressure is a trade off between yield and cost.
- Generating high pressures is expensive (vessels and pumps) and unsafe.
A vanadium pentoxide catalyst is also used to increase the rate of formation of sulfuric acid, speeding up the rate of reaction.
The catalyst does not change the equilibrium it just speeds up the reaction.
101
How do you optimise the Haber Process?
The haber process is used to produce ammonia (NH3) for use in fertilisers, explosives, cleaning products and pharmaceuticals.
N2(g) + 3H(g) <-> 2NH3(g)
^H = -43kJ mol^-1
102
Describe the energy cost when managing chemical process...
Economics important in industrial chemical processes. Energy is a huge cost!
103
How do you reduce energy cost?
Use heat energy (feedback into process or convert).
Operate at a lower temperature (e.g use a catalyst)
Run process continuously - starting and stopping takes more energy.
104
Why does hard water interfere with the process of saponification?
The soap consists of a charged hydrophilic head and a non-polar hydrophobic tail.
Hydrophobic tail should dissolve in non-polar grease and hydrophilic head should dissolve in water.
Agitation separates grease from the surface.
However, went a large concentration of Ca2+ and Mg2+ are in water, the anionic hydrophilic head is attracted to the cationic charge of the calcium and magnesium ions. Preventing the head from forming hydrogen bonding, preventing the micelles from being formed and the grease from being removed.
105
Describe the process of soil salinity
* High soil salinity effects water and therefore nutrient uptake by plant (via osmosis).
- Ca2+ and Mg2+ bind layers of clay.
- In cation exchange, they are replaced with Na+. This is larger. The electrostatic attraction is weakened causing separation of layers of clay.
- Structural collapse occurs, and the soil porosity and aeration is decreased, leading to decreased movement of water and gases
- Roots are unable to obtain water and penetrate soil. Soils can become waterlogged.
106
What are the advantages of zeolites
They have a very high surface area, increasing the efficiency of the ion exchange.
They are porous, allowing for water to flow through their chemical structure and maximise ion exchange.
107
