CHY111 Assignment 2 Chemistry Past Paper

# ASSIGNMENT-2: The conversion of cyclopropane to propene in the gas phase is a first order reaction with rate constant of 6.7 × 10⁻⁹ s⁻¹ at 500°C. **(a)** If the initial concentration of cyclopropane was 0.25 M, what is the concentration after 8.8 min? **(b)** How long (in min) will it take for t...

# ASSIGNMENT-2: The conversion of cyclopropane to propene in the gas phase is a first order reaction with rate constant of 6.7 × 10⁻⁹ s⁻¹ at 500°C. **(a)** If the initial concentration of cyclopropane was 0.25 M, what is the concentration after 8.8 min? **(b)** How long (in min) will it take for the concentration of cyclopropane to decrease from 0.25 M to 0.15 M? **(c)** How long (in min) will it take to convert 75% of the starting material? **→ (a) C₃H₆(g) → C₃H₆(g)** n = 1 ; k = 6.7 × 10⁻⁴ s⁻¹, T = 500°C = 773 K [A]₀ = 0.25 M, t = 8.8 min **Using,** [A]t = ln[A]₀ - kt => [A]t = e⁻ᵏᵗ x [A]₀ => [A]t = (e⁻6.7×10⁻⁴ × 8.8 × 60) × (0.25) [A]t = (0.25)e⁻⁰.₃₅₃₇₆ [A]t = 0.176 M **(b)** t = ? [A]₀ = 0.25 M , [A]t = 0.15 M **Using** ln[A]t = ln[A]₀ - kt => t = ln [[A]₀/[A]t] / k t = ln (0.25/ 0.15) / 6.7 × 10⁻⁴ => t = ln(5/3) × 1 / 6.7 × 10⁻⁴ t = 0.510 / 6.7 × 10⁻⁴ = 0.07611 × 10⁴ t = 761.1 sec => t = 761.1 / 60 = 12.685 min **(c)** t = ? percentage converted = 75% => [A]t / [A]₀ = (1 - 75/100) = (100 - 75) / 100 = 25 / 100 = 0.25 **To find t ;** t = ln[A]₀ / [A]t / k => t = ln (0.25) / 6.7 × 10⁻⁴ t = ln 4 / 6.7 × 10⁻⁴ = 1.386 / 6.7 × 10⁻⁴ = 0.20686 × 10⁴ t = 2068.6 sec => t = 2068.6 / 60 = 34.47 min