chapter 8 slides

# Its partial pressure p according to henrys law z s k

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its partial pressure, P , according to Henry’s Law: z s = k H P z k H is Henry’s constant, which depends in the gas, the solvent, and the temperature. z The law implies that, at constant temperature, doubling of the partial pressure of a gas doubles its solubility.

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Henry’s Constants
Example Problem z Calculate the solubility of carbon dioxide and neon in water at 20 °C and give a potential explanation for the difference. k H (CO 2 ) = 2.3 × 10 -2 , P = 3.6 × 10 -4 and k H (Ne) = 5.0 × 10 -4 , P = 1.8 × 10 -5 . z s = (2.3 × 10 -2 mol L -1 atm -1 ) × (3.6 × 10 -4 atm) z s = 8.3 × 10 -6 mol L -1 for CO 2 z s = (5.0 × 10 -4 mol L -1 atm -1 ) × (1.8 × 10 -5 atm) z s = 9.0 × 10 -9 mol L -1 for Ne

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Temperature and Solubility
Temperature and Solubility z Most gasses become less soluble as the temperature of the solution is raised. z A majority of solids become more soluble as the temperature of the solution is raised; however, there are many exceptions to this rule as well. z Some compounds, like sodium sulfate, can show mixed behavior depending on the speciation of the compound.

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Enthalpy of Solution z The change in enthalpy per mole of formula units when a substance dissolves is called the enthalpy of solution, Δ H sol . z The change in enthalpy can be measured calorimetrically from the heat absorbed or released when the substance dissolves at constant pressure. z The enthalpy of solution is the sum of the lattice enthalpy and the enthalpy of hydration: z Δ H sol = Δ H L + Δ H hyd
Enthalpy of Solution

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Free Energy of Solution z Dissolving depends on the balance between the change in entropy of the solution and the change in entropy of the surroundings. z A substance with a strongly positive enthalpy of solution is likely to be insoluble because the entropy of the surroundings may decrease so much the dissolution overall decreases disorder. z A solute dissolves spontaneously only until Δ G = 0, when a dynamic equilibrium is established.
Free Energy of Solution
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