Dalton's Law vs. Raoult's Law

[RedRifle31]

Is there a difference?


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[Bingwen]

Dalton's law is looking at total pressure of a system and Raoult's law is looking at vapor pressure. Raoult's you use the pressure of a pure solvent times the mole fraction to get the new pressure.

Dalton's law looks at if you add pressures together you get a total pressure and the pressure of a particular gas is the total pressure times the mole fraction.

They are similar but look at different things.

 

[Syxx]

To add on to Bingwen's post it's very important to distinguish the fact that partial pressure is not the same as the vapor pressure and that each law is looking at mole fraction in a different phase.

Partial pressure is simply the pressure exerted by one gas species in a mixture of gases. It is dependent only on the mole fraction of that species in the gas phase.

Vapor pressure by definition is the pressure of the vapor phase when the number of moles of that substance evaporating into the vapor phase is equal to the number of moles condensing into the condensed phase.

What Raoult's law allows you to do is calculate the partial vapor pressure of each component in a mixture. This is dependent on what the component is and how much of it there is in the condensed phase. After you get the partial vapor pressures of every component in the mixture then assuming the vapor phase you are looking it behaves like an ideal gas Dalton's law can be used to determine the total pressure of the vapor phase in that system.

 

[Bingwen]

To add on to Bingwen's post it's very important to distinguish the fact that partial pressure is not the same as the vapor pressure and that each law is looking at mole fraction in a different phase.

Partial pressure is simply the pressure exerted by one gas species in a mixture of gases. It is dependent only on the mole fraction of that species in the gas phase.

Vapor pressure by definition is the pressure of the vapor phase when the number of moles of that substance evaporating into the vapor phase is equal to the number of moles condensing into the condensed phase.

What Raoult's law allows you to do is calculate the partial vapor pressure of each component in a mixture. This is dependent on what the component is and how much of it there is in the condensed phase. After you get the partial vapor pressures of every component in the mixture then assuming the vapor phase you are looking it behaves like an ideal gas Dalton's law can be used to determine the total pressure of the vapor phase in that system.

Thank you for adding that!