Compared to the vapor pressure of ethanol at 1.0 atm and 25°C, the vapor pressure of water at 1.0 atm and 25°C is

Regents Chemistry Exam August 2025 Question 38

38 Compared to the vapor pressure of ethanol at 1.0 atm and 25°C, the vapor pressure of water at 1.0 atm and 25°C is

(1) lower because water has weaker intermolecular forces

(2) lower because water has stronger intermolecular forces

(3) higher because water has weaker intermolecular forces

(4) higher because water has stronger intermolecular forces

Solution:

Table H on the Reference table gives vapor pressures for different substances at various temperatures. The vapor pressure of ethanol at 25C is around 9kPa and that of water is around 5kPa. The vapor pressure of water is lower because it has stronger intermolecular forces. The stronger the intermolecular forces (forces of attraction between molecules), the harder it is for molecules to separate from one another go into gaseous phase. Less gas means lower vapor pressure. Choice 2 is the correct answer.

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