Physical Chemistry
What is an ideal gas and what is the equation that links pressure, volume, temperature and amount?
Ideal gas: particles with negligible volume and no forces between them. PV=nRT.
How does atomic radius change across a period and down a group? Give a short reason.
Across a period atomic radius decreases (increasing nuclear charge pulls electrons closer); down a group radius increases (extra electron shell)
Give the IUPAC definition of a transition metal in one sentence and name two first‑row transition metals.
IUPAC: element whose atom has an incomplete d subshell, or which can give rise to cations with an incomplete d subshell. Examples: Fe, Cu.
What is ΔH (enthalpy change of reaction)? Is bond‑making exothermic or endothermic?
ΔH is heat change at constant pressure. Bond‑making is exothermic.
What is the aim of a titration?
To find the unknown concentration of one solution by reacting it with a solution of known concentration.
For the reaction A → products with rate = k[A]^2, what does the k represent and how does doubling [A] affect the rate?
k is the rate constant; doubling [A] for second‑order doubles the rate by a factor of four.
What is first ionisation energy?
First ionisation energy = energy required to remove one electron from a gaseous atom
Why are scandium and zinc sometimes not counted as transition metals? Give a short electron‑configuration reason.
Sc3+ is 3d0 and Zn2+ is 3d10 so their common ions do not have incomplete d subshells.
State Hess’s law in one sentence.
Hess’s law: total enthalpy change for a reaction is the same regardless of the route taken.
Give one good practice tip for accurate mass measurement on a balance.
Tare the balance, use a clean dry weighing boat, avoid drafts and handle samples with clean tweezers.
What is activation energy in simple terms and where is it shown on a reaction energy diagram?
Activation energy = minimum energy needed for reactants to form products; shown as the peak (energy of transition state) above reactants on the energy diagram.
Explain why ionisation energy generally increases across a period.
Ionisation energy increases across a period because nuclear charge increases while shielding changes little, so electrons are held more strongly.
Name two common oxidation states of iron and say which has more unpaired d electrons (assume high‑spin where relevant)
Common: Fe2+ (d6) and Fe3+ (d5). Assuming high‑spin, Fe2+ has 4 unpaired electrons (d6 high‑spin) and Fe3+ has 5 unpaired electrons (d5)
What is Gibbs free energy formula and when is a reaction spontaneous in terms of ΔG?
ΔG=ΔH−TΔS; spontaneous if ΔG<0.
List the main steps to prepare a 250.0 cm3 standard solution from a solid sample.
Accurately weigh sample, dissolve in distilled water, transfer to 250.0 cm3 volumetric flask, rinse and make up to the mark, invert to mix.
How does increasing temperature change the fraction of molecules with enough energy to react?
Increasing temperature increases the proportion of molecules with energy ≥ Ea, so rate increases.
Give one example of an anomaly in first ionisation energy across a period (e.g., Mg→Al or P→S) and give a short reason for the anomaly.
Example: Mg → Al shows a small drop because the outer electron in Al enters a higher‑energy p orbital (less tightly held) compared with Mg’s s orbital. P → S anomaly: electron pairing in S causes extra repulsion, slightly lowering IE.
What is coordination number? Give the coordination number and shape for a typical octahedral complex.
Coordination number = number of ligand donor atoms bound to the metal. Octahedral complex: coordination number 6, shape octahedral.
If a process has negative ΔS but is still spontaneous, what must be true about ΔH (qualitative)?
ΔH must be sufficiently negative to overcome the unfavorable (negative) TΔS term so that ΔG is negative.
Name one experimental method to measure the enthalpy change of a reaction and one common source of error.
Use a calorimeter (e.g., coffee‑cup); common error: heat loss to surroundings or incomplete reaction.
Turn the Arrhenius equation into a linear formula, and state what a graph of ln(k) vs. 1/T will help you find.
ln(k) = -Ea/R * 1/T + ln(A). The gradient will help calculate Ea and the Y intercept will help calculate A.
Describe how shielding and effective nuclear charge affect trends in atomic radius and ionisation energy using one clear example.
Effective nuclear charge (Zeff) increases across a period as protons are added without much extra shielding, decreasing radius and increasing IE; shielding from inner shells reduces Zeff down a group (example: Na vs K — K has larger radius and lower IE due to added shell).
For a d4 metal ion in an octahedral field: in one sentence say what decides if it is high‑spin or low‑spin, and name a strong ligand and a weak ligand.
High‑ vs low‑spin depends on competition between pairing energy P and splitting Δoct: if Δoct > P → low‑spin; strong ligand example CN–, weak ligand example H2O.
Write the Arrhenius equation and say what the frequency factor A represents in simple terms.
k=Ae(−Ea/RT) A is the frequency factor — how often molecules collide with correct orientation.
In one sentence, how does atomic absorption spectroscopy (AAS) measure the concentration of a metal in solution?
AAS measures how much light at a specific wavelength is absorbed by free atoms of the metal; compare absorbance to standards to determine concentration.