## Chemistry and Chemical Reactivity (9th Edition)

From appendix G, the vapor pressure of water is: $@20°C: 17.5\ mmHg$ $@0°C: 4.6\ mmHg$ Partial pressures: A) $45/100×17.5=7.88\ mmHg$ B) $95/100×4.6=4.37\ mmHg$ Mol fraction of water vapor: A) $7.88/760×100\%=1.037\%$ $1.037/100×18.015=0.187\ g/mol\ air$ B) $4.37/760×100\%=0.575\%$ $0.575/100×18.015=0.104\ g/mol\ air$ Molar volume of air: $V/n=RT/P$ A) $V/n=0.082×293\ K/1\ atm=24.04\ L/mol$ B) $V/n=0.082×273\ K/1\ atm=22.40\ L/mol$ Thus, the mass of water per liter of air is: A) $0.187\ g/mol\div 24.04\ L/mol=0.0078\ g/L$ B) $0.104\ g/mol\div 22.40\ L/mol=0.0046\ g/L$ It's greater in A.