Final answer:
To estimate the temperature at which the vapor pressure of a substance is 90 kPa, one would use the Clausius-Clapeyron equation, input the given data, and solve for the unknown temperature.
Step-by-step explanation:
The question involves estimating the temperature at which a substance's vapor pressure is 90 kPa, given its vapor pressure at 30°C is 70 kPa, and its enthalpy of vaporization is 20 kJ/mol.
To approximate this temperature, we use the Clausius-Clapeyron equation, which relates the change in the vapor pressure to the change in temperature. The equation is ln(P2/P1) = -(AHvap/R)(1/T2 - 1/T1), where AHvap is the enthalpy of vaporization, R is the universal gas constant (8.314 J/(mol K)), and T1 and T2 are the initial and final temperatures in Kelvin, respectively.
When entering the values into the equation, and solving for T2, we will find the temperature that correlates with a vapor pressure of 90 kPa. The closest fitting answer from the options given will be the estimated temperature.