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Title: AP Chemistry Help: How to find delta H with bond energy? Post by: mikejones on Aug 22, 2012 the equation is
I2(g) + 3Cl2(g) = 2ICl3 (g) bond energies I-I = 150 Cl-Cl= 240 I-Cl = 210 I get -30 but there isn't even a 30 for the answer choices Title: AP Chemistry Help: How to find delta H with bond energy? Post by: Tom291 on Aug 22, 2012 To answer a question like this one, you need to add up all of the energy that is released by the formation of bonds, and subtract that which is expended to break bonds.
For this reaction, each mole of ICl3 formed forms three moles of I-Cl bonds. Two moles are formed, so that is six moles of I-Cl bonds formed. Each mole of I2 reacted breaks a mole of I-I bonds. One mole is reacted, so that is one mole of I-I bonds. Finally three moles of Cl-Cl are reacted, requiring the braking of three moles of Cl-Cl bonds. The reaction enthalpy is calculated from: (6 mol)(210 kJ/mol) - (3 mol)(240 kJ/mol) - (1 mol)(150 kJ/mol) = +390 kJ |