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Enthalpy of Solution ( H SOLN )

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When substances dissolve in water, an energy change usually occurs. Enthalpy of solution is defined as the enthalpy change when 1 mole of a substance completely dissolves (kJ mol -1 )

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Experiment 50cm 3 of H 2 O Thermometer Balance 2g NaOH or 4g NH 4 NO 3

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Measurements Taken Volume (mass) of water Mass of substance dissolves Temperature of water at start Temperature of water at end

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Specimen Results 1.03g of NaOH was dissolved in 50g (0.05kg) of water. The temperature of water rose by 5 o C. Calculate the enthalpy of solution of NaOH.

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1. Calculate energy change EH = c x m x ΔT = 4.18x0.05x5 = -1.045kJ 2. Calculate the number of moles of NaOH 1 mole NaOH=40g so 1.03g=1.03/40= 0.026 mol 3. Calculate enthalpy of solution 0.026 moles: 1.045kJ 1 mole : 40.2kJ

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Therefore the Enthalpy of solution= -40.2kJ Note that H SOLN can be a +ve or –ve value. You can work out which it is from the question.

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