hess\'s law When a reaction can be expressed as the algebraic sum of a sequence

Question

hess's law When a reaction can be expressed as the algebraic sum of a sequence of two or more simpler reactions the heat of reaction is the algebraic sum of the heats of these simpler reactions This generalization has been found to be true for every reaction that has been tested In this experiment you will use this generalization to determine the AH for a reaction that is difficult to measure directly using a Styrofoam calorimeter Magnesium metal burns very rapidly as you have observed in photo flash-bulbs releasing much light and heat The reaction is represented by the equation This equation can be obtained by combining equations (2), (3). and (4)

Explanation / Answer

Solution :-

Equations added in the part A are correct

Part B

Equation for the Delta H1 in the form of Delta H values is as follows

Delta H1 = Delta H2 + Delta H4 – Delta H3

Here delta H3 is subtracted because the equation is reversed therefore the value of Delta H remains same but the sign changes

Part C

Delta H reaction = sum of Delta Hf products – sum of delt aHf reactant

Delta H4 = [1*H2O(l)]-[(1*H2)+(0.5*O2)]

In the elemental state delta H formation = 0 kJ

Therefore delta Hf of the H2 and O2 = 0.0 kJ per mol

Now lets put the values in the formula

Delta H4 = [-285.8 kJ*1] –[(0.0*1)+(0.5*0.0)]

                = -285.8 kJ /mol

Te=herefore the delta H4 = -285.8 kJ /mol

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