Use bond energies to estimate the enthalpy change for the formation of HBr(g) from H2(g) and Br2(g). Given: BE(H-H) = 436 kJ/mol, BE(Br-Br) = 192 kJ/mol, BE(H-Br) = 366 kJ/mol.
A
103 kJ/mol
B
-230 kJ/mol
C
230 kJ/mol
D
-103 kJ/mol
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1
Identify the chemical reaction: The formation of HBr(g) from H2(g) and Br2(g) can be represented as: .
Calculate the total energy required to break the bonds in the reactants: Use the bond energies provided to find the energy needed to break one mole of H-H bonds and one mole of Br-Br bonds. This is calculated as: .
Calculate the total energy released when forming the bonds in the products: Use the bond energy of H-Br to find the energy released when forming two moles of H-Br bonds. This is calculated as: .
Determine the enthalpy change for the reaction: Subtract the total energy released from the total energy required. The enthalpy change is calculated as: .
Interpret the sign of the enthalpy change: If the result is negative, it indicates that the reaction is exothermic, meaning it releases energy. If positive, the reaction is endothermic, meaning it absorbs energy.