standard enthalpy vap. of acetic anhydride ((CH3CO)2O)=45.7 kJ/mol. normal BP is 139.6 C  vap. pressure of acetic anhydride at 125.6°C?

1 Answer

Relevance
  • 3 weeks ago
    Best answer

    Use the Clausius-Clapeyron equation. Temperatures need to be in Kelvin. The normal boiling point is the temperature at which a liquid boils at 1 atmosphere of pressure.

    Clausius-Clapeyron equation:

    ln(P₂/P₁) = (∆H°vap / R) x [(1/T₁) - (1/T₂)]

    P₁ = 1 atm

    T₁ = 139.6°C = (273.15 + 139.6) K = 412.75 K

    P₂ = ?

    T₂ = 125.6°C = (273.15 + 125.6) K = 398.75 K

    ∆H°vap = 45.7 kJ/mol = 45700 J/mol

    R = 8.314 J/(mol•K)

    Omitting the units to avoid clutter,

    ln(P₂/P₁) = (∆H°vap / R) x [(1/T₁) - (1/T₂)]

    ln(P₂ / 1) = (45700 / 8.314) x [(1/412.75) - (1/398.75)]

    ln(P₂) = -0.46757

    P₂ = e^(-0.46757)

    P₂ = 0.627 atm …….. to 3 sig figs

Still have questions? Get answers by asking now.