IIT JAM CY flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

First law of thermodynamics

The energy change of a closed system equals heat absorbed plus work done on it: ΔU = q + w. For expansion against constant external pressure, w = −P_extΔV.

Gibbs energy equation

ΔG = ΔH − TΔS. A process at constant temperature and pressure is spontaneous only when ΔG is negative; at equilibrium ΔG = 0 and ΔG° = −RT ln K.

Arrhenius equation

The rate constant varies as k = A exp(−Ea/RT). A plot of ln k against 1/T is linear with slope −Ea/R and intercept ln A.

First-order half-life

For a first-order reaction t½ = ln2/k ≈ 0.693/k. It is independent of the initial concentration, so each successive half-life has the same duration.

Particle in a one-dimensional box

For a particle of mass m in a box of length L, E_n = n²h²/(8mL²) with n = 1, 2, 3…. The lowest level has a non-zero zero-point energy.

Nernst equation

E = E° − (RT/nF) ln Q. At 298 K this becomes E = E° − (0.0592 V/n) log Q, where n is the number of electrons transferred.

Beer–Lambert law

A = εcl, where A is absorbance, ε the molar absorptivity, c the concentration and l the path length. Absorbances of non-interacting species at one wavelength are additive.

Clausius–Clapeyron equation

ln(P₂/P₁) = −(ΔH_vap/R)(1/T₂ − 1/T₁). It links vapour pressure to temperature, and the slope of ln P versus 1/T gives −ΔH_vap/R.

Spectrochemical series

Ligands ordered by increasing field strength: I⁻ < Br⁻ < Cl⁻ < F⁻ < OH⁻ < H₂O < NH₃ < en < NO₂⁻ < CN⁻ < CO. Strong-field ligands give large Δo and low-spin complexes.

Octahedral crystal field splitting

In an octahedral field the five d orbitals split into lower t2g (each −0.4Δo) and upper eg (each +0.6Δo). Δo grows with metal charge and ligand field strength.

Spin-only magnetic moment

μ = √(n(n+2)) Bohr magnetons, where n is the number of unpaired electrons. Orbital contribution makes observed moments of some ions exceed the spin-only value.

18-electron rule

Many stable organometallic complexes have 18 valence electrons at the metal, counting the metal d electrons plus two electrons from each two-electron donor ligand.

Jahn–Teller distortion

A nonlinear molecule with a degenerate electronic ground state distorts to lift the degeneracy. Octahedral d⁹ copper(II) and high-spin d⁴ complexes show marked tetragonal elongation.

HSAB principle

Hard acids such as Al³⁺ and Fe³⁺ prefer hard bases like F⁻ and O donors; soft acids such as Ag⁺ and Hg²⁺ prefer soft bases like S donors, I⁻ and CN⁻.

Lanthanide contraction

Poor shielding by 4f electrons steadily reduces ionic radius across the lanthanides, so Zr and Hf, and Nb and Ta, have almost identical sizes and very similar chemistry.

Chelate effect

Polydentate ligands form more stable complexes than comparable monodentate ligands because chelation releases more bound solvent molecules, increasing the entropy of the system.

SN2 mechanism

Bimolecular substitution with rate = k[RX][Nu]. A nucleophile attacks the carbon backside as the leaving group departs, inverting configuration; methyl and primary halides react fastest.

SN1 mechanism

Unimolecular substitution with rate = k[RX]. Slow ionisation gives a carbocation that is then captured by a nucleophile; tertiary substrates in polar protic solvents react fastest, with racemisation.

Markovnikov's rule

In electrophilic addition of HX to an alkene, hydrogen goes to the carbon with more hydrogens, placing the halogen on the more substituted carbon via the more stable carbocation.

Hückel aromaticity rule

A cyclic, planar, fully conjugated system with 4n+2 π electrons is aromatic; 4n π electrons give antiaromatic character. Benzene (6π) and cyclobutadiene (4π) illustrate this.

Cannizzaro reaction

Aldehydes with no α-hydrogen, such as methanal and benzaldehyde, disproportionate in concentrated base to give the corresponding alcohol and carboxylate salt.

Grignard reagent incompatibility

Grignard reagents act as strong bases and are destroyed by acidic hydrogens in water, alcohols, amines and terminal alkynes, so such groups must be protected or absent.

E2 elimination

Bimolecular elimination with rate = k[RX][base]. Proton and leaving group are removed in a concerted anti-periplanar fashion to give an alkene; bulky strong bases favour it.

Friedel–Crafts acylation

Acyl chloride with AlCl₃ generates an acylium ion that substitutes the aromatic ring to give a ketone. It fails on strongly deactivated rings and does not rearrange.

EDTA titration stoichiometry

EDTA complexes most metal ions in a 1:1 ratio whatever the charge. The conditional formation constant depends on pH, so the titration is buffered at a chosen value.

Mohr method

Chloride is titrated with silver nitrate using potassium chromate as indicator; red silver chromate appears at the end point. The solution must be nearly neutral.

Iodometric titration

An oxidising analyte liberates iodine from excess iodide, and the iodine is titrated with sodium thiosulfate. Starch is added near the end point and turns blue with iodine.

Retention factor in chromatography

k = (t_R − t₀)/t₀, where t_R is the analyte retention time and t₀ the time of an unretained solute. Values between about 1 and 5 are usually desirable.

Confidence interval

x̄ ± ts/√n, where t is the Student factor for n − 1 degrees of freedom at the chosen confidence level and s is the sample standard deviation.

Standard addition method

Known amounts of analyte are added to several aliquots of sample, and the response is extrapolated to zero signal; matrix effects are compensated because standards are in the sample matrix.

Hollow cathode lamp

A sharp-line source for atomic absorption spectrometry whose cathode contains the element being determined, so the emitted resonance lines match the analyte absorption lines.

Distribution ratio

D = total solute concentration in the organic phase divided by that in the aqueous phase. It sums all species present and determines the fraction extracted.