EXPERIMENT 10.B Enthalpy Combining these three equations yields the required equ

Question

EXPERIMENT 10.B Enthalpy Combining these three equations yields the required equation: Mg(s) + ½Odg)- MgO(s) Be aware that running an equation in the opposite direction simply changes the sign of the heat of formation Obtain 60 mL of IM HCI and measure its temperature. Weigh 0.6 g of magnesium and pla calorimeter. Add the HCl and report the highest temperature reached within several minutes of stirri re. Weigh 0.6 g of magnesium and place in the clean the calorimeter and again measure 60 mL of IM HCl. Weigh 1.0 g of Mgo calorimeter. Add the HCl solution and then measure the highest temperature as above. r and again measure 60 mL of IM HCI. Weigh 1.0 g of MgO and place in the

Explanation / Answer

Initial temperature of the solution is 24o C

Hightest temperature of the mixture is 380C

T = Final – Initial = 380C - 24o C

       = 140C

Mass of MgO = 1

Moles of MgO = Gram/ Mol.WT

                          = 1/ 40.3

                          = 0.02481mol

Heat gained by the solution

         q = (mCpT)soln

where m = mass (in grams)

           Cp = heat capacity (in J / g°C) at constant pressure

           T = Tfinal – Tinitial(°C)

These are solutions, not pure water. The specific heat of water is 4.184 J/goC. Assume that these solutions are close enough to being like water that their specific heats are also 4.1984 J/goC.

m=1 g

Cp= 4.1984 J/goC

T=14oC

Therefore

            q = (mCpT)soln

                     = 1g x4.1984 J/goC x 14oC

               = 56.77J

Heat lost by the reaction

qrxn=-qsoul

       = -56.77J

Heat of reaction per mole of MgO

   To calculate the energy per mole of any substance, divide the number of joules by the number of moles.

Energy per mole is nothing but molar enthalpy

Since molar enthalpy= qrxn / moles of MgO

                                 = -56.77J/ 0.02481mol

= -2288.19J/mol or -2.28819 kJ/mol

Heat of reaction of water = -285.9kJ/mol

Hrxn = Hf, products - Hf, reactants

                    Hf = Heat of reaction per mole of MgO + Heat of reaction of water

                            = -2.28819 kJ/mol + (-285.9kJ/mol)

                  Hf   = -288.2 kJ/mol

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