Definitions Flashcards
(106 cards)
1
Q
READ THE MATHEMATICS 3 TIMES
A
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2
Q
What are isotopes?
A
Atoms with the same number of protons but differing number of neutrons
3
Q
what are isobars?
A
Atoms with the same atomic weight but differing number of protons and electrons
4
Q
what are isotones?
A
Atoms with the same number of neutrons but differing atomic weights?
5
Q
what does the first quantum number represent?
A
n, the energy level quantum number, describes the proximity to source of attraction.
the higher the energy level, the further away the electron can be found
6
Q
what does the second quantum number represent?
A
l, the Angular quantum number, determines the shape of the electron cloud.
l=0, spherical shape (s orbital)
l=1, p orbitals
l=2, d orbitals,
l=3, f orbitals
L ranges from 0 to n-1
7
Q
what does the third quantum number represent?
A
m, the Magnetic quantum number, determines the orbitals orientation in space.
Values range from -L to L
8
Q
what does the fourth quantum number represent?
A
s, the Spin quantum number, is used used to explain behavior of individual electrons as if they were spinning clockwise or anticlockwise.
has value of plus/minus half
9
Q
what are the 5 Goldschmidt rules of element distribution?
A
- If two ions have the same radius and the same charge, they would enter solid solution in each mineral with equal ease in amounts roughly proportional to their abundance. The ionic radii must not differ more than 15%; substitution is limited or rare if radii differ by 15 to 30% and non-existent of the difference is more.
- When two ions possessing the same charge but different radii compete for a lattice site, the ion with the smaller radius would be incorporated preferentially because the smaller ion forms a stronger ionic bond.
- When two ions having different charges but similar radii compete for the same lattice site, the ion with the higher charge forms a stronger ionic bond and would be incorporated preferentially
- Ions whose charge differ by one unit may substitute for one another provided electrical neutrality of the crystal is maintained by coupled substitution.
- Nature of bond, i.e. degree of covalence should not change.
10
Q
What are the three types of molecular orbitals and which is the strongest?
A
Sigma, s, constructed from s-AO (strongest)
Pi, p, constructed from p-AO
Delta, d, constructed from d-AO
11
Q
what is electronegativity and how does it vary across the periodic table?
A
Electronegativity describes the power of an atom to attract electrons to itself in a chemical bond
Electronegativity increases towards the right and decreases towards the bottom of the periodic table
12
Q
describe the difference between ionic and covalent compounds in terms of PARTICIPATING ELEMENTS
A
IONIC
Commonly between two elements with quite different electronegativity’s, usually a metal and a nonmetal
COVALENT
Commonly between two elements with similar electronegativity’s, usually nonmetals. Homonuclear molecules (such as Cl2 comprised of only one element) are covalent
13
Q
describe the difference between ionic and covalent compounds in terms of MELTING POINT
A
IONIC
They are solids with high melting points (typically > 400°C). Ionic compounds do not exist as gases in nature
COVALENT
They are gases, liquids, or solids with low melting points (typically < 300°C)
14
Q
describe the difference between ionic and covalent compounds in terms of SOLUBILITY
A
IONIC
Many are soluble in polar solvents such as water, and most are insoluble in nonpolar solvents such as carbon tetrachloride (CCl4 ).
COVALENT
Many are insoluble in polar solvents, and most are soluble in nonpolar solvents such as carbon tetrachloride (CCl4)
15
Q
describe the difference between ionic and covalent compounds in terms of ELECTRICAL CONDUCTIVITY
A
IONIC
Molten compounds and aqueous solutions are good conductors of electricity because they contain charged particles (ions)
COVALENT
Due to lack of charged particles, liquid and molten compounds do not conduct electricity, and aqueous solutions are usually poor conductors of electricity
16
Q
what is metallic bonding?
A
Describes bonding that exists among atoms within the crystal structure of a metallic element
Most metallic elements display closed-packed structures
17
Q
what is van der Waals bonding?
A
Weak attractive and repulsive forces among the molecules
18
Q
what is a hydrogen bond?
A
forms between H atom in a polar bond such as O-H and an electronegative element such as O, N and Cl
19
Q
what are the four groups in Goldschmidt’s classification?
A
Siderophile (iron loving) elements
Chalcophile (sulphur loving) elements
Lithophile (rock loving) elements
Atmophile elements, which are normally found in the gas phase
20
Q
what is meant by chemical equilibrium? Recall the equations.
A
A reaction attains equilibrium when the rate of forward reaction becomes equal to the rate of the reverse reaction
The properties of the system will not change with time
21
Q
what is the Le Chatelier Principle?
A
This is nothing more than a description of the equilibrium constant
If a system in equilibrium is disturbed by some external influence, the system will react in such a way as to alleviate the disturbance.
22
Q
what is a homogeneous reaction in terms of thermodynamics?
A
A homogeneous thermodynamic system is defined as the one whose chemical composition and physical properties are the same in all parts of the system, or change continuously from one point to another.
In a system of this kind, acted upon by the force of gravity, both the composition of the system and its physical properties will continuously change from one point to another.
23
Q
what is a heterogeneous reaction in terms of thermodynamics?
A
A heterogeneous system is denned as one consisting of two or more homogeneous bodies.
The homogeneous bodies of a heterogeneous system are referred to as phases.
Each phase is separated from other phases by interfaces, or boundaries, and in passing over such a boundary the chemical composition of the substance or its physical properties abruptly change.
This phase boundary must not be regarded as a mathematical surface but as a thin layer separating the phases, a layer where the properties of one phase pass, or turn, rapidly into the properties of the other phase.
24
Q
what is the basis behind henrys law? Recall the equation
A
Henry’s law relates the fugacity of the gas to its activity in solution
25
Recall the variance equation. what do the three possible values of this equation tell us about the system?
When f = 0, the system is described by an ‘invariant point’
When f = 1, the system is described by ‘uni-variant curves’
When f = 2, the system is described by ‘di-variant curves’
26
state the first law of thermodynamics. Recall the equations
The energy in a system can neither be created, nor destroyed, only transferred from on form into another
The definition of energy is the ability to do work, thus, with energy comes the proceeding of geochemical reactions
The change in the internal energy, ∆U, of the studied thermodynamic system during a process is equal to the difference between heat, Q, and word done, W.
27
state the second law of thermodynamics
Any process leads to a change in order of the system, or entropy
The higher the randomness, the higher its entropy; the more organized a system, the lower its entropy
28
what is entropy? Recall the equations
Entropy is a measure of the spontaneous dispersal of energy at a specific temperature in a system
Entropy is highest in gaseous phases and lowest in solid phases
29
what are the two implications of the second law of thermodynamics?
Naturally occurring, or "spontaneous" processes will always proceed towards the state that has the least potential energy
Spontaneous chemical reactions increase the disorder in the system. We know from the first law of thermodynamics that energy cannot be lost, but it can change forms. What is lost, when a reaction is finished, is energy that is useful for doing more work
30
how can the change in enthalpy be determined? recall the formula
The change in enthalpy due to a reversible or irreversible change in the state of a system via a process can be determined by measuring the heat absorbed (or released) by the system during that change at constant pressure.
31
what is enthalpy? Recall the formula
The total heat content of a system.
It is equal to the internal energy of the system plus the product of pressure and volume.
32
what value is the change in enthalpy for an exothermic reaction?
heat is outputted, so the change in enthalpy is negative
33
what value is the change in enthalpy for an endothermic reaction?
heat is inputted, so the change in enthalpy is positive
34
where is enthalpy stored and how is it released?
Enthalpy is stored in chemical bonds: forming bonds liberates energy and breaking bonds requires energy.
Bond enthalpy is the enthalpy change required to break and separate 1 mole of bonds in a molecule of a gaseous compound.
The strength of the bonds in the reactants and products decides whether a reaction is exothermic or endothermic.
35
what is heat capacity? recall the formula
The heat capacity of a substance is the amount of heat required to raise the temperature of 1 mol of substance by 1 ̊C
36
how many heat capacities describe a system? recall the formulae
A system has two values of heat capacity, one for heat being added at constant pressure and one for heat being added at constant volume
if volume is constant, he heat absorbed equals the change in internal energy.
if pressure is constant, the heat absorbed goes into both temperature rises and expansion
37
what is gibbs free energy and how can we compute it? recall the formula.
∆G expresses the ability of substances to react and the extent to which reactions will go
The free energy is not directly measurable for any system, but its value can be computed from its enthalpy and entropy
38
what are the three key points about the gibes free energy?
Negative ∆G indicates that the reaction is exergonic and spontaneous.
If the reactants have a lower ∆G than the products, there will be an increase in free energy, and the reaction is
non-spontaneous.
• In this situation, energy (in the form of heat, light, etc.) will be required for the reaction to take place.
A spontaneous reaction will not necessarily occur on its own.
• This is because an initial activation energy is needed to start the reaction and even a spontaneous reaction
may need some form of energy input.
39
why is chemical potential used in thermodynamics? recall the relevant formula
To extend the application of the auxiliary thermodynamic functions to systems that may undergo a change in composition
The chemical potential of a constituent i is its partial molar free energy at constant temperature and pressure.
40
what does the extent of a reaction allow us to do?
To find conditions of equilibrium at constant temperature and pressure for a reaction in terms of chemical potentials
41
what is activity a measure of? recall the formula
Activity is a measure of the effective concentration of a species in a mixture.
By convention, activity is treated as a dimensionless quantity, although its actual value depends on customary choices of standard state for the species. The activity of pure substances in condensed phases (solid or liquids) is
normally taken as unity (the number 1).
42
what does the activity of a species depend upon?
Activity depends on temperature, pressure and composition of the mixture, among other things
43
for gases, what is the effective partial pressure referred to as?
fugacity
44
why is there a difference between activity, as well as other measures, in a composition?
Molecules in non-ideal gases or solutions interact with each other, either to attract or to repel each other. The activity of an ion is particularly influenced by its surroundings.
45
what are activities used to define?
Activities should be used to define equilibrium constants, but, in practice, concentrations are often used instead.
The same is often true of equations for reaction rates.
However, there are circumstances where the activity and the concentration are significantly different and, as such, it is not valid to approximate with concentrations where activities are required.
46
recall the relationship between the gibbs free energy of a system and the equilibrium constant.
what three points can be made about this relationship?
This relationship is universally valid, with the two sides of the equation referring to completely different physical situations, it is only a numerical equality
The left-hand side refers to the energy change of a reaction involving substances at chosen standard state without the connotation of an equilibrium state.
The right-hand side refers to a system in which the constituents have achieved mutual equilibrium under the pressure-temperature-composition conditions of interests.
47
what is the reactant quotient?
Q
ratio of product activities to reactant activities.
48
what is a rate law? recall the rate law for aA + bB -> cC
an expression for the reaction rate in terms of the concentration of the species that occur in the overall chemical reaction.
49
what is the overall order of the reaction: aA + bB -> cC
a+b
50
what is an integrated rate law?
an expression for the concentration of a reactant or product as a function of time
51
what is meant by the phrase half life? recall the formula
The half-life of a reaction is the time it takes for the concentration to fall to half of its value.
52
in a first order reaction, what do we plot? what does the line look like? recall the formula
linear line
LN(initial conc / current conc) vs. t
53
what is the activation energy? recall the relationship between the rate constant and the activation energy
energy required to initiate a reaction
54
what happens if the activation energy is large/small?
the rate of reaction is slow/fast
55
how is activation energy represented?
Plotting the reaction pathway of energy versus reaction progress shows the energy relations in a reaction requiring activation.
The reactions go forward only at the rate which some of its particles acquire enough energy to get over the ‘energy hump’ represented by the activation energy, Ea.
56
what are the four main points regarding dissolution of silicate minerals?
The initial reaction is a rapid non-stoichiometric dissolution, giving a solution with much higher Sodium/Silicon ratios and Aluminium/Silicon ratios slightly higher than those in the original mineral
The large dissolution rates in the first days are best explained with formation of surface layers that have been altered, loss of Sodium by exchange with Hydrogen ions and dissolution of very fine particles.
The straight lines after 5 to 10 days indicate that the rate is constant or at a steady state and their slopes show that the dissolution is congruent.
A rate constant for steady state dissolution of albite in what with a pH of 5.6 can be estimated from the experimental data.
57
what is a catalyst? define the two different forms?
a substance that accelerates the rate of a thermodynamically favourable chemical reaction without being transformed or consumed itself.
A catalyst cannot make a thermodynamically unfavourable reaction possible
homogenous, entire reaction in a single phase
heterogeneous, surface or contact catalyst
58
what are the two main processes for mass transfer in an aqueous solution?
Mass transfer by advection is the most important process for redistributing chemical components in the earth.
The driving force of advection is gravity, whereby fluids move upwards or downwards due to density differences with their surroundings.
Advection serves to transport reactants and therefore speeds up reactions, however, it is rarely effective on very small scales.
On these small scales, diffusion, the spontaneous dispersion of ions and molecules into a fluid or solid, is usually the process responsible for the transportation of chemical components.
Except in gases, diffusion is too slow to transport components more than a few meters.
Consequently, mass transfer and chemical transport generally involve both advection and diffusion, with advection for large-scale transport and diffusion for small scale transport.
59
why does water act as a solvent?
High polarity and an angular momentum.
Formation of large Clusters
60
what is ion strength? recall the formula
The electrostatic forces between charged solute species in an aqueous solution depend on the charges of the species and the total concentration of the specie
61
what is a base?
A base is a molecule or ion capable of uniting with H+, a proton acceptor, or containing OH- that yields OH- on dissolving in water.
62
what is an acid?
An acid is a molecule or ion that can give H+ to another molecule or ion, a proton donor.
63
what is pH? recall the formula
The pH gives the concentration of protons in the system.
64
how do we differentiate between a strong and weak acid? recall the acid dissociation constant
Large Y values indicate a small ZYI.
if pKa > 0, the acid is weak
if pKa < 0 the acid is strong
Strong acids will dissociate fully and the H+ concentration is simply given by the molarity of the acid.
65
what is the difference between an open and closed system in thermodynamics?
In a system open to the atmosphere, we consider the exchange of gases with the atmosphere
In a system that is closed to the atmosphere, we treat the acid as a non-volatile acid.
66
what is acidity of a solution?
the capacity of a solution to donate protons.
67
what is the alkalinity of a solution?
the capacity of a solution to accept protons.
68
what is a buffer and what is it made of? recall the formula for the buffer intensity
Buffers are solutions which can resist changes in pH on addition of acid or alkali.
Buffers usually consist of either a solution of weak acid in the presence of one of its salts, or a solution of a weak base in the presence of one of its salts.
69
define the concept of solubility?
The solubility of a substance in water is the concentration of the substance in water that is in equilibrium with the substance at pressure and temperature of interest.
70
where do we find ion pairs? what is there effect on a system?
In more concentrated solutions, we find the formation of dissolved complex ions due to short range interactions among opposite charged ions.
This has an important effect on mineral dissolution, with solubility and ion strength being positively correlated.
71
recall the saturation index formula. was are the key values?
if S = 0 then the solution is just saturated
if S > 0 then the solution is super-saturated, the solution should precipitate since the dissolved salt is to restore equilibrium
if S< 0 then the solution is under saturated, some more of the salt can be dissolved in the solution to achieve saturation
72
what are the four factors affecting calcite solubility?
Temperature
The solubility of calcite and other forms of calcium carbonate in pure water decreases as temperature rises.
Pressure
The effect of pressure by itself, independent of its effect on FŒ', is to increase the solubility of calcite slightly.
This is important in the deep sea, where solubility increases to about twice its surface value
Organic Activity
Many organisms use calcium carbonate in the construction of their shells.
Green plants may cause precipitation of calcium carbonate indirectly by removing CO2 from water during photosynthesis.
pH and CO2
most important controls, inversely correlated to one another
Precipitation of calcite is favoured by an increase in pH
73
what are the three influences for calcite precipitation?
Mechanical disturbances.
Dust particles in the solution.
Unevenness of surfaces in contact with the solution.
74
what is the carbonate concentration depth?
CCD
Below this depth, seawater is under-saturated with respect to calcite.
75
what are the two factors affecting silica solubility?
Temperature
The solubility of silicates in pure water increases somewhat as the temperature rises unless the temperature exceeds 1000°C (for a pressure of 1000bars).
Pressure
The effect of pressure itself is, independent of its effect on FŒ', to increase the solubility of silicates slightly.
76
what are the three types of adsorption surfaces?
Mineral particles
Organic particles
Colloids, particles that occupy the size range between true solution and suspension: 10 and 0.01 μm
77
what are the three types of surface attachment in adsorption? describe each
Physical adsorption
Van der Waals interactions that are long range but weak
Chemical adsorption
Molecules stick to the surface by forming a chemical bond, usually covalent in nature
Hydrophobic adsorption
Many organic substances are highly insoluble in water
These substances become adsorbed to surfaces because they are repelled by water
78
what are the three types of surface complexes? describe each
Inner sphere complexes
Surface complexes that involve some degree of covalent bonding between the surface and ions
Outer sphere complexes
Form when one or more water molecules intervenes between the surface and the ions
Electrostatic forces
Ions held in the diffusive layer
79
how does water interact with surfaces during adsorption?
Metal ions on a mineral surface are incompletely coordinated leading to a partial charge on the surface.
When the mineral surface is immersed in water, water molecules coordinate metal ions on the surface.
Water molecules dissociate leaving hydroxyl groups coordinating with metal ions.
Protons will associate with surface oxygen.
80
how can we determine surface charge?
If the amount of acid or base added is known, the surface charge can be determined by measuring the pH.
There is a defined pH at which a mineral surface has no charge, the point of zero charge, or PZC.
We define the point of zero net proton charge, or PZNPC, when the charge due to the binding and release of protons is zero.
An important feature of the PZC is that it is independent of ionic strength
81
what does the force exerted on ions by surface charge do? recall the gouy-chapman theory
gives rise to an electric potential
82
what is the adsorption isotherm and what assumptions are made about it?
The variation of adsorption with concentration at a chosen temperature is called the adsorption isotherm.
This isotherm model is called the Langmuir model, which is now derived for the adsorption of gases on mineral surfaces.
ASSUMPTIONS
Adsorption cannot proceed beyond monolayer coverage
All sites are equivalent and the surface is uniform
The ability of a molecule to adsorb at a given sire is independent of the occupation of neighbouring sites
83
what is coordination?
Ions in solutions often associate with other ions, forming new species called complexes
Complex formation is important because it affects solubility and reactivity of ions.
Complexation is usually described in terms of a central ion, generally a metal, and ions or molecules that surround it, or coordinate it, referred to as ligands.
The atoms, molecules, or ions involved tend to improve the stability of their electron configuration, that is, of the electrons in their outer shell
Any combination of cations with molecules or anions containing a free pair of electrons, bases, is called coordination or complex formation and can be electrostatic, covalent or a mixture of both.
84
what two species are in coordination?
The metal cation is called the central atom and the anions or molecules are referred to as ligands.
85
what happens if a ligand consists of more than one atom?
If a ligand is composed of several atoms, the one responsible for the basic or nucleophilic nature of the ligand is called the ligand atom.
If a base has more than one ligand atom and this can occupy more than one coordination number, it is referred to as a multi-dentate complex.
86
what are the two complexes in water coordination?
The most common complexes are formed between metals and water.
Beyond aqua-complexes, we distinguish two different types of complexes, often called inner sphere complexes:
Ion pairs
Complexes where the two ions are in contact and a bond forms between them that is at least partly covalent
87
what happens in hydrolysis?
The positive charge of the central ion tends to repel hydrogen in the water molecules so that water molecules in the aqua-complexes are more readily hydrolysed.
The power of a metal to hydrolyse is a function of the ratio of ion charge to ionic radius
88
recall the ability of a metal to hydrolyse as a function of z/r. what happens for each size of this value?
SMALL
Hydration
INTERMEDIATE
Extracts OH-
Forms Insoluble Complexes
HIGH
Extracts O^2-
Forms soluble oxy-anion
89
What is an A type metal?
A, or hard, metals have an inert gas type electron configuration.
90
what is a B type metal?
B, or soft, metals have a more readily deformable electron sheet.
The complexes of B metals tend to have more covalent character.
91
how can ligands be classified in relation to A and B type metals?
Certain ligands tend to form more stable complexes with type A metals, with others forming more stable complexes with B metals.
This led to a classification of ligands into type A ligands, which tend to complex with type A metals, and type B ligands, which tend to complex with type B metals.
92
what is oxidation?
Oxidation is defined as a reaction involving the loss of one or more electrons.
93
what is reduction?
Reduction is defined as a reaction involving the gain of one or more electrons.
94
what is the oxidation state a measure of?
The oxidation state is a measurement of the degree of oxidation of an atom
95
what is an electrochemical cell used for?
To study the electrochemical processes or measure electrochemical potentials in the environment
96
what makes up an electrochemical cell?
A cell consists of two electrodes, or metallic conductors, which are in contact with an electrolyte, an ionic conductor, which may be liquid or solid in phase.
An electrode and its electrolyte compromise an electrode compartment.
A huge variety of electrodes are used: metal/metal ion, gas, metal/insoluble salt and redox.
The simplest type of cell has a single electrolyte common to both electrodes.
97
what happens in an electrochemical cell?
When a spontaneous reaction takes place, electrons are deposited in one electrode (the site of oxidation, the anode) and collected from another (the site of reduction, the cathode), resulting in a net flow of current which can be used to do work.
98
what is meant by cell potential? recall the formula
A cell in which the overall cell reaction has not reached chemical equilibrium can do electrical work as the reaction drives electrons through an external circuit.
The work that a given transfer of electrons can accomplish depends on the potential difference between the two electrodes.
When the cell reaction is at equilibrium, the cell potential is zero.
Cell potential can then be related to the activities of the participants in the cell reaction.
99
what does the nernst equation tell us? recall the formula.
sed to calculate the electromotoric force, or emf, of an oxidation-reduction reaction under any condition.
100
what is the standard electrode potential? recall the formula
The established convention is to measure potentials in a standard hydrogen electrode cell at STP.
The cell consists on one side of a platinum plate coated with fine platinum powder that is surrounded by hydrogen gas, maintained at a partial pressure of 1 atm and emerges in a solution of unit H+ activity.
A potential of zero is assigned to the half-cell reaction.
The other side consists of the electrode and solution under investigation.
101
what is the harned cell?
Silver Chloride Electrode
The procedure for measuring a standard potential can be illustrated by considering a specific case of the silver chloride electrode.
102
what is The Saturated Calomel Electrode (SCE)?
The saturated calomel electrode is a reference electrode based on the reaction between elemental mercury and mercury (I) chloride.
It has been widely replaced by silver chloride electrodes, however, the SCE has a reputation for being more robust.
The aqueous phase in contact with the mercury and the mercury (I) chloride is a saturated solution of potassium chloride in water.
103
what is the pe concept? recall the formula and relation with the equilibrium constant
it is a theoretical unit and concept
The greater pe, the greater the tendency of species to lose their valance electrons
When an electron acceptor is abundant relative to the abundance of electron donors, the pe is high and electron donors will be in electron-poor states
104
how can we assess the stability limits of water?
To make predictions about geological processes, we need at least a rough idea as to the ranges of natural E and pH values.
The upper limit for pH-E in nature is given by the stability of water in contact with the atmosphere, recalling that O2 is the strongest oxidizing agent found in nature.
The lower (reducing) limit of stability is given by the evolution of H2.
105
what are the limitations in a pe vs pH diagram?
We assume we know all the components that are likely to be present.Consequently, E-pH diagrams are over simplified
We also need to know the concentrations of the species
They ignore colloids and non-stated species
Each diagram considers only one set of p-T conditions
106
describe the significance of redox chemistry in nature.
In the natural environment, the natural oxidizing agent is atmospheric oxygen and the major reducing agent is organic carbon.
The oxidation of organic matter first utilizes the dissolved oxygen in the system.
If the amount of oxygen is limited, the decomposition proceeds with the reduction of nitrate, nitrite and sulphate.
Redox interface between aerobic and anaerobic groundwater:
The redox interface or redox front is a zone of rapidly changing E.
This zone may be sharp or extend over only several millimetres or it may extend over many meters and tens of meters.
The Role of Micro-Organisms:
Microorganisms play an important role in facilitating several chemical reactions which are based on the transfer of electrons.
