Hess

             MgSO4 + 7H2O =  MgSO4•7H2O.
             As we can not measure this enthalpy change directly, we will use the following two equations to calculate the enthalpy change for the equation above.
             MgSO4 + H2O =  Mg2+ + SO42- + H2O.
             MgSO4•7H2O + H2O =  Mg2+ + SO42- + 7H2O + H2O.
             To determine the change in enthalpy of each equation, we use the formula: ∆H=m.s.∆T, where ∆H is the change in enthalpy (measured in Joules per unit mass - eg. joules per 15.5 grams), m is the mass of either the anhydrous or hydrated magnesium sulfate, measured in grams, s is the specific heat capacity of water (4.18Jg-1K-1), and ∆T is the change in temperature, measured in Kelvin. .
             Then, the value obtained for ∆H for each equation, is converted in to kilojoules by dividing by one thousand, and then converted into kilojoules per mole.
             One of these values will be exothermic (the one in which the temperature increased), and the other will be endothermic (the one in which the temperature decreased). To get a value for the enthalpy change of the equation:.
             MgSO4 + 7H2O =  MgSO4•7H2O.
             Take the ∆H.
             As we did this experiment twice, I will do two sets of Data Collection, & Analysis.
             Data Collection (1) :.
             ANHYDROUS MAGNESIUM SULFATE.
             Time (seconds) Temperature (°C) Observations.
             0 19.9 White powder, chalky.
             20 24.2 White, fizzy.
             40 26.0 .
             60 26.2 White, murky.
             80 26.2 Smells like chalk.
             100 26.2 .
             120 26.2 Still murky, still smells.
             Mass of MgSO4 = 7.5010g ± 0.0005g.
             Mass of H2O = 100.0g ± 0.5g.
             Change in temperature = 6.3°C ± 0.1°C.
             HYDRRATED MAGNESIUM SULFATE.
             Time (seconds) Temperature (°C) Observations.
             0 20.5 White granules.
             20 20.0 Milky white.
             40 19.8 .
             60 19.0 Milky white.
             80 18.5 .
             100 18.3 Colourless & clear.
             120 18.0 .
             140 18.3 Still colourless.
             Mass of MgSO4•7H2O = 15.5030g ±0.0005g.
             Mass of H2O = 100.0g ±0.5g.
             Change in temperature = 2.5°C ±0.1°C.
             Data Analysis (1):.
             MgSO4.
             Error analysis: mwater = 100.