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Henry's Law

 

 

 

At a constant temperature, the amount of a given gas dissolved in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid.

P=KC 

P=pressure of the gas (atm)  K=Henry's Law Constant (atm/M)

 C=Concentration of the Gas  (M)

Examples-The Henry's law constant for He gas in water at 30C is 2.70 x 103 atm/M. The constant for N2 at the same temperature is 1.67 x 103 atm/M. If the two gases are each present at 1.43 atm pressure, calculate the solubility, in M, of each gas.

P=KC  or P/K=C

He 
1.43 atm
/ 2.70x103 atm = 5.30 x10-4 Molar


N2
1.43 atm/ 1.67 x 103 atm = 8.56 x10-4 Molar

 

***Watch the units  some chemist use the equation S=KP  (solubility= Henrys constant x pressure)

Henrys constant will have the units of    M/atm  for this equation

Example-The Henry's Law constant for the solubility of nitrogen in water is 6.40x10^-4 M/atm at 25.0 Celsius. At .750 atm how many grams of N2 can be dissolved in .250 L of water at 25.0 degrees Celsius

Answer-S = (6.40 x 10^-4 M/atm)*(0.750 atm) = 4.8 x 10^-4 M

 

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