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The vapor pressure of ethanol is [tex]1.00 \times 10^2[/tex] mmHg at [tex]34.90^\circ C[/tex]. What is its vapor pressure at [tex]55.32^\circ C[/tex]? (ΔH_vap for ethanol is 39.3 kJ/mol)

Answer :

Vapor pressure of ethanol is 286 mmHg.

We can use the Clausius-Clapeyron equation to calculate the vapor pressure of ethanol at 55.32°C:

  • ln(P2/P1) = (ΔHvap/R)(1/T1 - 1/T2)

where:

  • P1 is the vapor pressure of ethanol at 34.90°C

  • P2 is the vapor pressure of ethanol at 55.32°C

  • ΔHvap is the heat of vaporization of ethanol (39.3 kJ/mol)

  • R is the gas constant (8.314 J/mol K)

  • T1 is the temperature of ethanol at 34.90°C (34.90 + 273.15 = 308.25 K)

  • T2 is the temperature of ethanol at 55.32°C (55.32 + 273.15 = 328.67 K)

We can plug these values into the equation to solve for P2:

  • ln(P2/1.00×10^2 mmHg) = (39.3 kJ/mol)/(8.314 J/mol K)(1/308.25 K - 1/328.67 K)

  • P2/1.00×10^2 mmHg = 0.286

  • P2 = 0.286 * 1.00×10^2 mmHg

  • P2 = 286 mmHg

Therefore, the vapor pressure of ethanol at 55.32°C is 286 mmHg.

About Vapor pressure

In chemistry, vapor pressure is the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system. The equilibrium vapor pressure is an indication of a liquid's thermodynamic tendency to evaporate. The pressure exhibited by vapor present above a liquid surface is known as vapor pressure. As the temperature of a liquid increases, the attractive interactions between liquid molecules become less significant in comparison to the entropy of those molecules in the gas phase, increasing the vapor pressure.

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