Exams › JEE Main › Chemistry

For the acid-catalysed hydrolysis of ethyl acetate, CH3COOC2H5(aq) + H2O ->[H+] CH3COOH(aq) + C2H5OH(aq), the observed rate law is rate = k[ester][H2O][H+]. With water in large excess (about 55.5 M), the reaction is pseudo-first-order in ester. If k = 1.386*10⁻³ M⁻² min⁻¹ and [H+] = 1.8 M, how many seconds will it take for the ester concentration to fall to half its initial value?

1. 300
2. 150
3. 600
4. 277

Correct answer: 300

Solution

With [H2O] ~ 55.5 M and [H+] = 1.8 M, k' = 1.386*10⁻³ * 55.5 * 1.8 = 0.1385 min⁻¹, so t(1/2) = 0.693/0.1385 = 5 min = 300 s.

Related JEE Main Chemistry questions

• For the reaction A → products, the half-life is 120 min when the initial concentration of A is 8.0 × 10⁻² M. If the starting concentration is changed to 4.0 × 10⁻² M, the half-life increases to 240 min. What is the reaction order?
• For a first-order process A → B, if the rate constant is k and the starting concentration of A is 0.5 M, what is the half-life?
• For the elementary gas-phase reaction A(g) + 2B(g) → C(g) + D(g), an experiment starts with initial partial pressures p_A = 0.60 atm and p_B = 0.80 atm. If the partial pressure of C becomes 0.20 atm, then the reaction rate compared with the initial rate is
• From the experimental data below for the reaction A + B → products, identify the rate law that fits the observations. Exp. 1: [A] = 0.012, [B] = 0.035, initial rate = 0.1 Exp. 2: [A] = 0.024, [B] = 0.070, initial rate = 0.8 Exp. 3: [A] = 0.024, [B] = 0.035, initial rate = 0.1 Exp. 4: [A] = 0.012, [B] = 0.070, initial rate = 0.8
• A radioactive substance is accidentally spread on the floor of a room. If its half-life is 30 days and the initial activity is 10 times the allowed safe level, after how many days will it become safe to enter the room?
• For the reversible reaction A2 + B2 ⇌ 2AB, the activation energies are 180 kJ mol⁻¹ for the forward direction and 200 kJ mol⁻¹ for the reverse direction. If a catalyst reduces the activation energy of both directions by 100 kJ mol⁻¹, what will be the enthalpy change of the reaction A2 + B2 ⇌ 2AB in the catalyzed pathway (in kJ mol⁻¹)?

⚔️ Practice JEE Main Chemistry free + battle 1v1 →