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Gas Pressure Over Water Equation:
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The gas pressure over water equation calculates the partial pressure of a gas collected over water by subtracting the water vapor pressure from the total measured pressure. This accounts for the contribution of water vapor to the total pressure in the system.
The calculator uses the gas pressure equation:
Where:
Explanation: When a gas is collected over water, the total pressure includes both the pressure of the gas and the vapor pressure of water. This equation isolates the pressure contribution from the dry gas alone.
Details: Accurate gas pressure calculation is essential for determining the true amount of gas produced in chemical reactions, calculating gas volumes at standard conditions, and ensuring precise measurements in gas collection experiments.
Tips: Enter total pressure and water vapor pressure in Pascals (Pa). Ensure the water vapor pressure value is appropriate for the temperature at which the gas was collected. Water vapor pressure must be less than total pressure.
Q1: Why do we subtract water vapor pressure?
A: Water vapor contributes to the total pressure measurement. Subtracting it gives the true partial pressure of the dry gas being measured.
Q2: How do I find the water vapor pressure?
A: Water vapor pressure depends on temperature and can be found in standard reference tables or calculated using appropriate formulas for the specific temperature.
Q3: What units should I use for pressure?
A: While Pascals (Pa) are used here, the equation works with any consistent pressure units (atm, mmHg, etc.) as long as all values use the same unit.
Q4: When is this calculation necessary?
A: This calculation is essential whenever gases are collected over water in laboratory experiments, particularly in chemistry demonstrations and gas law experiments.
Q5: What if the water vapor pressure exceeds total pressure?
A: This is not physically possible as water vapor pressure cannot exceed the total system pressure. Please verify your input values.