Let us define a new reference state as \"elements as monatomic gas atoms\" Thus

Question

Let us define a new reference state as "elements as monatomic gas atoms" Thus we will define our formation heats now as being "The enthalpy required to form 1 mole of molecules from elements as monatomic gases." d.) Using the following energy values, calculate the new formation value for each of the reactants and produce in the previous reaction. 111.88 kJ/mol Br (l) Br(g) H2 (g) H(g) C(graphite) C(g) 716.68 kJ/mol New AH Substance CH4 Brz(g) CH3Br(g) HIB Br2 hite H2(g) e.) Now, using the new values and using the products minus reactants approach, calculate the enthalpy of the reaction. Compare with the previous values.

Explanation / Answer

d) substance CH4

dHf = 1 x 716.68 + 4 x 217.97 = 1588.56 kJ/mol

Substance Br2(g)

dHf = 2 x 111.88 = 223.76 kJ/mol

Substance CH3Br(g)

dHf = 1 x 716.68 + 3 x 217.97 + 1 x 111.88 = 1482.47 kJ/mol

Substance HBr(g)

dHf = 1 x 716.68 + 1 x 111.88 = 828.56 kJ/mol

Substance Br2(l)

dHf = 2 x -111.88 = -223.76 kJ/mol

Substance Cgrahite

dHf = 716.68 kJ/mol

Substance H2(g)

dHf = 2 x 217.97 = 435.94 kJ/mol

e) If the reaction is, CH4 + Br2 ---> CH3Br

dHfrxn = 1482.47 - (1588.56 - 223.76)

           = 117.67 kJ/mol

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