Pressure & Dalton's Law

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Presentation Transcript

Gases : 

Gases Pressure & Dalton’s Law of Partial Pressures

Pressure : 

Pressure When gas particles collide with the walls of their container, they exert a force This force is called pressure Pressure is determined by: Number of gas particles Temperature of the gas

Standard Atmospheric Pressure : 

Standard Atmospheric Pressure 101.325 kPa 760 mmHg 760 torr 14.7 psi 1 atm 29.92 inHg All of these representthe same pressure – Standard AtmosphericPressure – just in different pressure units

Converting Pressure Units : 

Converting Pressure Units Write down what you’re given Conversion factor: Cancel units and solve

Example : 

Example Convert: 477 kPa = ___________ torr What would the pressure 26.5 psi be if it were expressed in units of in Hg?

Measuring Pressure : 

Measuring Pressure Pressure Gauge – used to measure the pressure of a gas inside a container (bike tire, basketball, oxygen tank, etc.) Manometer – measures the pressure of a sample gas Open – compared to atmospheric pressure Closed – absolute measure

Dalton’s Law of Partial Pressures : 

Dalton’s Law of Partial Pressures In a mixture of gases, the total pressure of the mixture equals the sum of the individual gas pressures Ptotal = Pgas1 + Pgas2 + … + Pgasn When a gas is collected over water, you have a mixture of your sample gas as well as water vapor

Slide 8: 

When dealing with a gas collected over water, you must determine the pressure of the dry gas Pgas = Ptotal - Pwater Determine Pwater by looking at a table of Water Vapor Pressure values

Water’s vapor pressure at various temperatures : 

Water’s vapor pressure at various temperatures

Dalton’s Law Example : 

Dalton’s Law Example A quantity of gas is collected over water at 8ºC. The manometer indicates a pressure of 84.5 kPa. What would the pressure of the dry gas be at 8ºC? Pgas(P1) = Ptotal – Pwater = 84.5 kPa – 1.1 kPa = 83.4kPa Pwater = 1.1 kPa