Presentation on theme: "Enthalpy of Solution ( H SOLN ). When substances dissolve in water, an energy change usually occurs. Enthalpy of solution is defined as the enthalpy."— Presentation transcript:
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 )
Experiment 50cm 3 of H 2 O Thermometer Balance 2g NaOH or 4g NH 4 NO 3
Measurements Taken Volume (mass) of water Mass of substance dissolves Temperature of water at start Temperature of water at end
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.
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
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.