Chemistry Labs

International Chemistry Olympiad · 1978

Problems

  1. Problem 4A vessel of volume 5.0 dm3^3 was filled with ethane at 300 K and 101.325 kPa, sealed, and then heated. The measured pressures were: at 300 K: 101.3 kPa (theoretical p′=101.3p'=101.3 kPa); at 500 K: 169.8 kPa (p′=168.7p'=168.7 kPa); at 800 K: 276.1 kPa (p′=269.9p'=269.9 kPa); at 1000 K: 500.7 kPa (p′=337.4p'=337.4 kPa). (a) Explain why the measured pressure exceeds p′p' at higher temperatures and write the reaction equation. (b) Calculate the degree of conversion α\alpha and equilibrium constant KpK_p at 800 K and 1000 K. (c) Using the integrated van 't Hoff equation ln⁡(Kp,2/Kp,1)=−ΔH∘R(1T2−1T1)\ln(K_{p,2}/K_{p,1}) = -\frac{\Delta H^\circ}{R}\left(\frac{1}{T_2}-\frac{1}{T_1}\right), calculate the mean reaction enthalpy ΔH∘\Delta H^\circ between 800 K and 1000 K. (R=8.314R = 8.314 J mol−1^{-1} K−1^{-1})Solutions: 1