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Explain the enthalpy of dilution. |
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Answer» SOLUTION :Enthalpy of dilution is the enthalpy change observed with the addition of a specified amount of solute to the specified amount of SOLVENT at a constant temperature and pressure. e.g., enthalpy change for dissolving 1 mol of gaseous hydrogen CHLORIDE in 10 mol of water can be represented by the following equation : `HCI_((g)) + 10_(aq) to HCI . 10_("aq") ., Delta H = -69.01` kj/mol Let us consider the following set of enthalpy change `(S-1) HCI_((g)) + 25_("aq") to HCI.25_("aq") Delta H= -72.03` kj/mol `(S-2) HCI_((g)) + 40_("aq") to HCI.40_("aq") Delta H= -72.79` kj/mol `(S-3) HCI_((g)) + oo_("aq") to HCI.oo_("aq") Delta H= -74.85` kj/mol The value of `DeltaH` show general dependence of the enthalpy of solution on amount of solvent. As more and more solvent is used, the enthalpy of solution approaches a limiting value, i.e., The value in infinitely DILUTE solution for NCl this value of `DeltaH` is given above in eq. (S-3) If we substrate the (S-1) from (S-2), `HCI.25_("aq")+ 15_("aq") to HCI.40_("aq")` `DeltaH= [-72.79 - (-72.03)]=-0.76` kj/mol This is enthalpy of dilution. It is the heat withdrawn from the surroundings. Other additional solvent is added to the solution. The enthalpy of dilution of a solution is dependent on the original concentration of the solution and amount of solvent added. |
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