The vapor pressure of methanol is 143 mmhg. identify the best reason to explain why methanol spontaneously evaporates in open air at 25.0∘c and standard pressure (760 mmhg). the vapor pressure of methanol is 143 . identify the best reason to explain why methanol spontaneously evaporates in open air at 25.0 and standard pressure (760 ). under these nonstandard conditions, the partial pressure of methanol is lower than its vapor pressure. calculations for a closed container show a partial pressure of methanol lower than its vapor pressure. the calculated standard free energy change corresponds to a spontaneous reaction. heat can be added under these nonstandard conditions to increase the vapor pressure of methanol.