GPAT Physical Chemistry Syllabus

How is molality (m) defined?

Molality = number of moles of solute per kilogram of solvent (mol/kg). It is temperature-independent.

Define mole fraction of a component in a solution.

The ratio of the number of moles of that component to the total number of moles of all components in the solution.

State Henry's law for gas solubility.

At constant temperature, the solubility (mass) of a gas in a liquid is directly proportional to the partial pressure of the gas above the liquid: p = K_H × x.

Define oxidation and reduction in terms of electron transfer.

Oxidation is the loss of electrons; reduction is the gain of electrons (mnemonic: OIL RIG — Oxidation Is Loss, Reduction Is Gain).

What is a redox reaction?

A reaction in which oxidation and reduction occur simultaneously, involving the transfer of electrons between species.

Define oxidizing agent and reducing agent.

An oxidizing agent gains electrons and is itself reduced; a reducing agent loses electrons and is itself oxidized.

What is the oxidation number of oxygen in most compounds, and what is the common exception?

Usually −2; the exception is peroxides where it is −1 (and OF2 where it is +2).

What is the oxidation number of hydrogen in most compounds, and the exception?

Usually +1; the exception is metal hydrides (e.g., NaH) where it is −1.

Define a disproportionation reaction.

A redox reaction in which the same element in a single oxidation state is simultaneously oxidized and reduced (e.g., 2H2O2 → 2H2O + O2).

What are the four common types of redox reactions?

Combination, decomposition, displacement, and disproportionation reactions.

Define the rate of a chemical reaction.

The change in concentration of a reactant or product per unit time (e.g., mol L⁻¹ s⁻¹).

What is the difference between average rate and instantaneous rate?

Average rate is the change in concentration over a finite time interval; instantaneous rate is the rate at a particular instant, given by the slope of the tangent to the concentration–time curve.

State the rate law expression for a general reaction.

Rate = k[A]^x[B]^y, where k is the rate constant and x, y are the orders with respect to A and B.

Define order of a reaction.

The sum of the powers of the concentration terms in the experimentally determined rate law.

Define molecularity of a reaction.

The number of reacting species (atoms, ions, or molecules) that collide simultaneously in an elementary reaction; it is always a whole number.

List four factors that affect the rate of a reaction.

Concentration of reactants, temperature, presence of a catalyst, and surface area (and nature of reactants).

State the Arrhenius equation and what it describes.

k = A·e^(−Ea/RT), describing the dependence of the rate constant k on temperature; Ea is the activation energy and A is the frequency factor.

Define activation energy.

The minimum amount of energy that reactant molecules must possess for a reaction to occur (the energy barrier between reactants and products).

How does a catalyst increase reaction rate?

It provides an alternative reaction pathway with lower activation energy, without being consumed in the reaction.

Why does boiling point of a solvent rise when a non-volatile solute is added?

The non-volatile solute lowers the solvent's vapour pressure, so a higher temperature is needed to make vapour pressure equal atmospheric pressure — this rise is boiling point elevation.

Give the formula for boiling point elevation.

ΔTb = Kb × m, where ΔTb is the elevation, Kb is the molal boiling point elevation (ebullioscopic) constant, and m is molality.

Give the formula for freezing point depression.

ΔTf = Kf × m, where ΔTf is the depression, Kf is the molal freezing point depression (cryoscopic) constant, and m is molality.

What are colligative properties?

Properties that depend only on the number of solute particles in solution, not their nature: relative lowering of vapour pressure, boiling point elevation, freezing point depression, and osmotic pressure.

What is the van't Hoff factor (i) and why is it used in colligative property calculations?

i is the ratio of observed to calculated colligative effect; it accounts for dissociation or association of solute particles (e.g., i ≈ 2 for NaCl).

Why is salt spread on icy roads in winter?

Salt dissolves and depresses the freezing point of water, causing ice to melt at lower temperatures (freezing point depression).

State the First Law of Thermodynamics.

Energy can neither be created nor destroyed, only converted from one form to another; the internal energy of an isolated system is constant. ΔU = q + w.

In the equation ΔU = q + w, what does each term mean (IUPAC sign convention)?

ΔU = change in internal energy; q = heat added to the system (positive when absorbed); w = work done on the system (positive when done on it).

Define enthalpy (H) and give its relation to internal energy.

Enthalpy is the heat content of a system at constant pressure: H = U + PV; the change is ΔH = ΔU + PΔV.

What is the work done in an isothermal reversible expansion of an ideal gas?

w = −nRT ln(V2/V1) = −2.303 nRT log(V2/V1).

For a reaction at constant volume, how does heat relate to internal energy?

At constant volume no PV work is done (w = 0), so the heat absorbed equals the change in internal energy: q_v = ΔU.

Define Arrhenius acids and bases.

An Arrhenius acid produces H⁺ (hydrogen) ions in aqueous solution; an Arrhenius base produces OH⁻ (hydroxide) ions in aqueous solution.

Define Brønsted–Lowry acids and bases.

A Brønsted–Lowry acid is a proton (H⁺) donor; a Brønsted–Lowry base is a proton acceptor.

Define Lewis acids and bases.

A Lewis acid is an electron-pair acceptor; a Lewis base is an electron-pair donor.

What is a conjugate acid–base pair?

Two species that differ by a single proton (H⁺); the acid loses a proton to form its conjugate base, and the base gains a proton to form its conjugate acid (e.g., HCl/Cl⁻).

Define pH and give its formula.

pH is the negative logarithm of hydrogen ion concentration: pH = −log[H⁺]. Neutral = 7, acidic < 7, basic > 7.

What is the ionic product of water (Kw) at 25°C and the relation between pH and pOH?

Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°C, and pH + pOH = 14.