Physical Chemistry & Stoichiometry — Part 2: 40 MCQs with Explanations

Oxalic acid is dibasic (n-factor = 2). Equivalent weight = 126/2 = 63 g/equiv.

Molar mass of CaCO3 = 40 + 12 + 48 = 100 g/mol. Number of moles = given mass / molar mass = 50/100 = 0.5 moles.

At dynamic equilibrium, the rates of forward and reverse reactions become equal. As a result, the net concentrations of reactants and products do not change with time.

State functions depend only on the initial and final state of the system, not the path taken. Enthalpy (H), Internal Energy (U), Pressure, Volume, and Temperature are state functions. Heat and work are path functions.

Absolute zero (0 K) is the temperature at which all molecular motion theoretically ceases, meaning the kinetic energy of gas molecules becomes zero.

At the anode, oxidation occurs. In aqueous NaCl, the possible reactions are 2Cl- -> Cl2 + 2e- and 2H2O -> O2 + 4H+ + 4e-. Due to overvoltage and concentration, chloride ions are oxidized more easily than water, producing chlorine gas.

Molar mass CO2 = 44 g/mol. 44g = 1 mole CO2. 1 molecule CO2 has 3 atoms. So, total atoms = 3 * NA = 3 * 6.022 x 10^23 = 1.806 x 10^24.

Ideal gas law assumes that the volume of gas molecules is negligible. At high pressures, the gas is compressed, and the volume of the molecules themselves becomes a significant fraction of the total volume, leading to deviation.

The triple point on a phase diagram is the unique temperature and pressure at which the solid, liquid, and gas phases of a substance are in thermodynamic equilibrium with each other.

The equilibrium constant (Kc) describes the ratio of products to reactants at equilibrium. It does not provide any information about the speed (rate) at which equilibrium is reached. Rate is affected by T, concentration, surface area, and catalyst.

This is the definition of the standard enthalpy of formation (ΔH°f). It is a fundamental quantity used in thermochemistry.

Graham's Law states that at constant temperature and pressure, the rate of diffusion or effusion of a gas is inversely proportional to the square root of its molar mass (or density).

A very large equilibrium constant (Kc >> 1) indicates that at equilibrium, the concentration of products is much greater than that of reactants. This means the forward reaction is highly favored and proceeds nearly to completion.

Vinegar is typically composed of 4-8% acetic acid (CH3COOH) in water. It is produced by the fermentation of ethanol.

According to Graham's law, the rate of diffusion is inversely proportional to the square root of molar mass. Hydrogen (H2) has the lowest molar mass (2 g/mol) among the options, so it will diffuse the fastest.

A catalyst works by providing an alternative reaction pathway that has a lower activation energy. This increases the rate of both forward and reverse reactions equally, so it does not change the equilibrium constant or shift the equilibrium.

In an isochoric process, the volume is constant, so ΔV = 0. Work done (w) is given by -PΔV (or -PextΔV). If ΔV=0, then w=0. Therefore, ΔU = qv (heat absorbed at constant volume).

At STP, 1 mole of any gas occupies 22.4 dm³. Number of moles = Volume in dm³ / 22.4 dm³/mol = 5.6 / 22.4 = 0.25 moles.

According to Graham's law of diffusion, the rate of diffusion is inversely proportional to the square root of its molar mass. Lighter gases diffuse faster. NH₃ (M=17 g/mol) is the lightest among the options.

The equilibrium constant Kc = [Products]/[Reactants]. If Kc > 1, the numerator (products) is larger than the denominator (reactants), meaning the reaction favors the products at equilibrium.

A catalyst increases the rate of a chemical reaction by providing an alternative pathway with lower activation energy. It is not consumed in the reaction and does not change the equilibrium constant.

At STP, 1 mole of any gas occupies 22.4 dm³. Therefore, 2 moles of O₂ will occupy 2 × 22.4 dm³ = 44.8 dm³.

For a zero-order reaction, rate = k [A]⁰ = k. So the rate constant has the same units as the rate of reaction: concentration per time (e.g., mol dm⁻³ s⁻¹).

Using Ideal Gas Law: PV = nRT. T = 27 + 273 = 300 K. P = (nRT)/V = (0.1 × 0.0821 × 300) / 2.46 = (2.463) / 2.46 ≈ 1 atm.

The pH scale runs from 0 to 14. pH 7 is neutral. pH less than 7 is acidic. A pH of 3 is far from 7 and indicates a high concentration of H⁺ ions, making it strongly acidic.

At dynamic equilibrium, the forward and reverse reactions continue to occur at equal rates. There is no net change in the concentrations of reactants and products.

The standard enthalpy of formation (ΔHf°) is defined as the heat change when one mole of a compound is formed from its constituent elements in their standard states under standard conditions (298 K and 1 atm).

The salt bridge (containing an inert electrolyte like KCl) serves multiple purposes: it completes the electrical circuit, maintains electrical neutrality by allowing ion flow, and prevents the mixing of the two electrolyte solutions.

According to Boyle's Law (at constant temperature and number of moles), pressure is inversely proportional to volume (P₁V₁ = P₂V₂). If volume is doubled (V₂ = 2V₁), then pressure becomes half (P₂ = P₁/2).

pH greater than 7 indicates a basic solution. Sodium hydroxide (NaOH) is a strong base, so its aqueous solution will have a pH greater than 7.

Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. Examples: NaOH, CaCl₂.

Tincture of iodine is a disinfectant solution containing 2-7% elemental iodine and potassium iodide (KI) dissolved in a mixture of alcohol and water. The alcohol (ethanol) is the primary solvent.

Molar mass of H₂O = 18 g/mol. Number of moles in 9g = 9/18 = 0.5 moles. Number of molecules = moles × Avogadro's number = 0.5 × 6.02 × 10²³ = 3.01 × 10²³.

According to the first law of thermodynamics, ΔE = Q + W, where Q is heat added to the system and W is work done on the system. If the system does work on the surroundings, then W (work done on system) is negative (-W). So ΔE = Q + (-W) = Q - W.

A catalyst speeds up both the forward and reverse reactions equally, so it helps the system reach equilibrium faster but does not change the position of equilibrium or the value of the equilibrium constant.

According to Henry's Law, the solubility of a gas in a liquid is directly proportional to the pressure of the gas above the liquid. Increasing pressure forces more gas molecules into the solution.

Molality (m) is defined as the number of moles of solute dissolved per kilogram (1000 g) of the solvent. It is temperature-independent because it is based on mass.

Mole (mol) is the SI base unit for amount of substance. One mole contains exactly 6.022 × 10²³ elementary entities (Avogadro's number).

One mole of H₂O contains 6.022 × 10²³ molecules. Each molecule has 3 atoms, so total atoms = 3 × 6.022 × 10²³ = 18.066 × 10²³.

Mole ratio: C = 40/12 = 3.33, H = 6.67/1 = 6.67, O = 53.33/16 = 3.33. Simplest ratio = 1:2:1 ⇒ CH₂O.