CHEM1031

CHEM1031 Study NotesAssumed Knowledge

Acid - proton donor

Base - proton acceptor

Acidic oxides (non-metals) react with water to make acids or bases to form salts (CO2). Basic oxides (metals) react with acids to form salts but do not react with alkaline solutions (CuO, Fe2O3). Amphoteric oxides (Al, Zn, Pb, Sn) react with acids or bases to form salts. Neutral oxides (CO, N2O) dont react.

acid + metal H2 + salt

acid + carbonate CO2 + H2O + salt

GasesDistinguishing properties of gases:

very compressible

flow rapidly

take shape of and fill a container (liquids only take shape)

expand and contract with temperature changes (more so than liquids, solids is near negligible) infinitely expandable (unlike liquids, solids)

low density

Gas variables:

Pressure (Pa)=force/area. Due to particles in motion, colliding with momentum into each other and walls. 1Pa = 1N/m2 = 1J/m3 (1N = 1kgm/s2)

1atm = 760mmHg/Torr

= 101325Pa

= 101.325kPa

= 1.01325bar

= 14.7psi

Volume (m3 - 103L) number/Amount (mass - kg, moles)

Temperature (always in Kelvin; absolute temperature)These are dependent upon each other in the three Empirical Gas Laws: Boyles Law - V EQ \F(1,P) (or P1V1 = P2V2) - as pressure increases, volume decreases Charles Law - V T (or EQ \F(V1,T1) = EQ \F(V2,T2) ) - as temperature increases, volume increases Avogadros Law (also Gay-Lussacs - found when gases reacted volumetric ratios were small whole numbers - a stochiometric ratio) - V n (or EQ \F(V1,n1) = EQ \F(V2,n2) ) - as the number of moles increases, so does the volumeCombining Boyles and Charles Law:PV T or EQ \F(P1V1,T1) = EQ \F(P2V2,T2) Combining all three forms the Ideal Gas Law:PV nT

or

PV = nRTwhere R = Universal Gas Constant

= 8.3145 J mol-1 K-1 (SI)

= 0.082057 L atm K-1 mol-1Standard Temperature and Pressure (STP): 0oC (273.15K) and 1 bar (1.00105Pa or 0.98atm). 1 mole of gas at STP is 22.7L. We can also sub in n=m/M and density ( - rho) = m/V to integrate other values.

Daltons Law of Partial Pressures - in a mixture of gases, total pressure is the sum of the pressure each gas would exert if alone under the same conditions (assuming the gases are independent and do not react):

PT = Pa + Pb + Pc +

Mole Fraction - for each component A in a mixture, the mole fraction is (a value between 0 and 1 - not percentage - to express the percentage of moles of that substance in a mixture):XA = EQ \F(nA,nT)

Partial Pressure of A PA = XAPT

Each gas also obeys the Ideal Gas Law independently as if they took up all the volume, and hence were PT=PA+PB, PAV=nRT and PBV=nRT. However these conclusions in the 17th-19th century, and it wasnt until the 19th-20th century that a theory of atoms began to form, so these laws all looked at macroscopic ideas, influenced by what we know to be properties of microscopic atoms.Kinetic Theory of Gases:

molecule size is negligible compared to distance between them

molecules move randomly in straight lines in all directions at various speeds

forces of attraction/repulsion are negligible (because they are very weak) except in collisions

gas particle collisions are perfectly elastic

Ek av absolute temperatureThis explains Boyles Law as less space means more frequent collisions, and hence higher pressure (as collisions result in a force applied), and Charles Law as increasing temperature, kinetic energy (molecule speed) increases, so collisions become more frequent and with greater force.Kinetic theory states Ek av is only dependent on temperature, not gas type, and difference gases at the same temperature have the same average kinetic energy. As k = m2/2, heavier gases will travel more slowly with the same energy. It can be found that (dont need to know derivation):k = EQ \F(3RT,2NA) NA is Avogadros number. Remember this is per molecule, so to find per mole multiply by Avogadros number. Combining this with our other formula for k:Rate of Gas Movement: rms = EQ \r( \F(3RT,M) ) Root-mean-square (rms) simply means we have square-rooted the mean value.Effusion - escape of molecules through a hole of molecular dimensions (assuming no collisions between molecules)Diffusion - mixing of gases until the mixture is homogeneous

Using the above rate and these ideas (in diffusion it could be two gases reacting and producing a colour located at a particular point and speeds) we can determine molecular mass.

Grahams Law - The rates of effusion (and diffusion) of two gases at the same temperature and pressure are inversely proportional to the square roots of their densities (note time is inversely proportional to rate): EQ \F(rate1,rate2) = EQ \F(\r(1), \r(2)) EQ \F(rate1,rate2) = EQ \F(\r (M2),\r(M1)) EQ \F(time1,time2) = EQ \F(\r(M1),\r(M2)) All gases are actually non-ideal: all particles do have volume - becomes significant at high pressure (real volume > ideal volume as ideal volume hits zero)

they have attractive forces - significant at low temperatures (real volume < ideal volume as particles are brought together; gases with low interatomic dispersion forces like He do not experience this)

particles do interact - negligible at high temperature (enough energy to keep bonds apart), but significant at other temperatures (real pressure < ideal gas pressure as there are less molecules - chemically bonded together - and hence less collisions)

All known life depends upon the atmosphere, however the atmosphere doesnt have a definite end, with 99% within 30km, outer space at ~10,000km.

Atomic StructureOnly valence electrons determine chemical properties, and hence isotopes have nearly identical chemical properties. Light is electromagnetic radiation (a self-sustaining oscillation of electric and magnetic fields), and is characterised by its frequency ( - nu; Hz or sec-1) or wavelength (; m or angstrom==10-10m), which are related by c=, with visible light being 3.9-7.0 10-7m, whilst gamma rays are around 10-12m and long radio waves 104.Monochromatic Radiation - a selection of one frequency (in practicality, a narrow band of frequencies) for various scientific measurements

Polychromatic Radiation - consisting of many frequencies

Light has typical wave-like properties (refraction, diffraction and interference), however also exhibits the photoelectric effect, discovered in 1887 by Hertz who found light could eject electrons from the surface of a metal, and a current could flow to another electrode in a vacuum. He also found it required a threshold frequency that was dependent on the type of metal used which was independent of the intensity, however once above the threshold frequency the intensity increased current size, and the energy of the electrons emitted depended on the frequency. In 1905, Einstein realised light comes in packets or quanta (got Noble Prize in 1921), where each quantum of energy is proportional to frequency:E = hwhereh = Plancks constant = 6.6261034Js

A photon with enough energy could be absorbed and eject an electron, producing a current, and only one with enough energy could overcome the attraction of the atom, the remainder energy being converted to kinetic (Ek = h-W). The energy of a particular orbital can be found by the Rydberg Equation:

EQ \F(1,) = RH EQ \b(\F(1,n12) - \F(1,n22)) whereRH = Rydberg constant for H (on data sheet)

n1 = lower shell

n2 = upper shell

For hydrogen the shell is a good indicator of electron energy: E = -RH/n2White (polychromatic) light passing through a gas composed of single atoms gas lines (or specific frequencies) removed, forming an absorption spectrum (the release of the photons once electrons fall is in all directions, and hence much weaker at the detecting screen; a prism can be used to distinguish between colours). When heating a gas by electrical discharge, it produces these series of lines in an emission spectrum. This is because electrons occupy discrete energy states that they move up or down. The spectra vary with the gas used and pressure (proximity alters energy of shells).Lyman = UV Balmer = visible light Paschen = IR

The value of n for each energy level/shell is the principal quantum number. The ground state is an atoms lowest state, however it can undergo transitions to higher excited states by heating or colliding energetically with other bodies. These are unstable and result in the lowering of energy levels by emission of photons.Complete removal of an electron means the electron has been moved to n=. The energy required to move a valence electron upwards is called the ionisation energy.

Solutions to the Schrdinger equation have exact analytical forms for the hydrogen atom:

=Ewhere = Hamiltonian (an operator that corresponds to the total energy of the system - encompasses nature of proton and electron particles and their Coulombic attraction [the electrostatic attraction or repulsion between protons and electrons])

E = energy of the state (a constant of proportionality) (psi) = the wavefunction

An eigenstate (or orbital) is an allowed energy (or shell) under the contraints of the Schrdinger equation (labelled by quantum numbers - they are the outcomes or results when solving the equation). These are wave-like states with 3D shape and amplitude (this form is a direct consequence of the Schrdinger equation. The electron density (probability of an electron being at a certain point) is given by the square of the wavefunction (however the Heisenberg uncertainty principle limits the ability to know both the position and energy (thus speed) of a quantum particle like an electron):=2As the electron could be at any distance from the nucleus (although further is less probable, the volume with a 90% chance of an electron being there is called the boundary surface, and this surface is thought of as the spatial limit of the atomic orbital. There are four quantum numbers to label each electron: principal quantum number (n) - 1, 2, 3, ,

azimuthal (angular momentum) quantum number (l) - 0, 1, 2, , (n-1)

magnetic quantum number (ml) - 0, 1, 2, , l (but counted from negative to positive: -l, -l+1, , 0, , l-1, l) spin quantum number (ms) - A set of orbitals with the same n are called a shell (in hydrogen all orbitals are in the same shell as there is one electron), and a set of orbitals with the same n and l are part of the same sub-shell, labelled by letters (called orbital symbols): if l=0 s orbital if l=1 its a p orbital if l=2 its a d orbital if l=3 its an f orbital then g, h, i and so on

This is written as:(n)(orbital symbol)no. of electrons

e.g. 2s2s orbitals are spherically symmetric, however the inner orbitals often deflect the outer orbitals (by Coulombic repulsion) resulting in their electron densities peaking further away.p orbitals consist of two lobes of electron density on opposite sides of the nucleus with a nodal plane (zero electron density) between them. As there are three ml values, there are three types of orbitals: px, py and pz.d orbitals have either a cloverleaf shape (dxy, dyz, dxz, dx2-y2) or two lobes and a torus (dz2).

The Coulombic attraction between the nucleus and electrons leads to a contraction of shells as you move to the right of the periodic table, requiring more energy to pull the electron out due to the increasing nuclear charge. Multi-electron atoms are more difficult to obtain analytical solutions of through the Schrdinger equation as the electrons repel each other, however we can still approximate orbitals that resemble the hydrogen atom. These repulsions are considered electronic shielding, and do not affect the electrons of an outer shell equally: s electrons of an outer shall have at least one smaller lobe of density closer to the nucleus (inside the region of shielding electron) and hence are less affected as they are more often closer in and not further out the effect is smaller for p orbitals, then d, then f, and so on

Thus the degree of shielding goes s solid

particles spread further

solution > solid + liquidenergy localised in solid spreadsgas + liquid > solutionenergy spreads even further in gas

C2H6 > CH4

more bonds to spread energy across3mol > 2mol

entropy amount (spreads across more molecules)

20K>10K

more kinetic energy=collisions, spreads energyNote that phase (position entropy) tends to dominate molecular complexity, as the molecules can spread further apart. Knowing which is greater, we can deduce whether the S of a reaction will be positive or negative (by doing final-initial).Standard entropies (S0) are the entropy change from T=0K (where S=0) to T=298K (25oC). We can find entropy by:S = EQ \F(q,T) The propensity for energy to spread out is known in the 2nd Law of Themodynamics:

Suniverse = Ssystem + SsurroundingsFor any spontaneous process, Suniverse > 0. Using data from tables (having fH0 in kJ/mol and S0 in J/K/mol - REMEMBER UNITS), we can then determine the difference between reactants and products, and hence if a reaction will be spontaneous at 298K. Using the above value of S for surroundings, and using q=H, it can be shown that for a spontaneous process:G = Hsystem - TSsystem < 0

This is called Gibbs Free Energy, a measure of the spontaneity of a process and the useful energy available from it. For ALL chemical reactions, a graph of G against the mole fraction of a reactant/product will have a minimum, and that minimum occurs at equilibrium. As G0, K0. The tables provided are for reduction potentials (not oxidation), so everything will be backwards and upside down from HSC. Note that unlike the equilibrium constant, this does not depend on the stoichiometry, and hence multiplying by a specific number does not change the cell potential.

When the electrodes themselves are part of the chemical reaction, they are called active electrodes. We can also use inert materials like graphite (often used for halogen gases) or platinum, called inactive electrodes. They conduct electrons, but do not partake in the reaction. Generally their reactions involve a gas or another ion. Electrodes are always placed on outside of the shorthand notation, regardless if active or inactive. Initially a standard hydrogen electrode was used to make measurements off, however this is difficult to replicate accurately (as concentration may vary with the gas), so it was initially replace with a normal and then saturated calomel electrode, however this contained mercury, so now we use a silver/silver chloride standard electrode, where E0=0.22V. Using a number line, and knowing which reaction is more positive, we can deduce the other electrodes standard potential.

As concentration affects cell potential, we use a standard concentration in E0, being 1M. Varying the concentration will involve Le Chateliers principle, and if it shifts to the right the cell potential will increase, whilst shifting to the left it will decrease. This is quantified in the Nernst Equation:

Ecell = E0 - EQ \F(RT,nF) ln EQ (Q)whereEcell = the maximum potential a cell can generate (V)

E0 = cell potential if c=1M

R = 8.314 J/K/mol (universal gas constant - note units)

T = temperature (K)

n = number of electrons transferred per mole of reagent

F = Faraday constant = 96485C/mol (on data sheet) = charge of 1 mol(e-)

Q = reaction quotient (current ratio of [products]/[reactants]Alternatively, at standard conditions (T=25oC):Ecell = E0 - EQ \F(0.0592,n) log10( EQ Q)If Q>1 (more product than reactants), Ecell