Gases produced by a chemical reaction can easily be collected over water. To determine the pressure of the dry gas, the vapor pressure of the water at that temperature must be subtracted from the total pressure. 1) Consider the following reaction: Mg(s) + 2 HCl(aq) MgCl(aq) + H(g) The total pressure of gas collected over water is 680.0 mmHg and the temperature is 22.5C What is the pressure of hydrogen gas formed in mmHg? Pressure = mmHg Water Vapor Pressure Table Temperature (C) 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 22.5 23.0 23.5 24.0 24.5 25.0 25.5 26.0 Pressure (mmHg) 15.5 16.0 16.5 17.0 17.5 18.1 18.6 19.2 19.8 20.4 21.1 21.7 22.4 23.1 23.8 24.5 25.2