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Calculating The Enthalpy of PbO -> Pb + 1/2 O2

November 5th, 2008

Free Chemistry Tutor Help Problem

Calculate the enthalpy change for the formation of PbO from Pb to O2 using this reaction
Pb+CO —-> PbO + C ΔH = -106.8KJ
2C + O2 —–> 2CO     ΔH = -221.0KJ

Answer

This is the examples of Thermochemistry that can be solve using Hess Law. rearrange the known reaction into the reaction that the problem wants. You need to calculate this reaction:

PbO -> Pb + 1/2 O2 ΔH= ?

First step we want PbO on the left or to be as reactant from the first reaction above PbO is on the right thus we should reverse this reaction

PbO + C -> Pb + CO ΔH= 106.8 KJ

second we need to reverse the second reaction above thus we get O2 on the left and divide the reaction with two to get the reaction coefficient of O2 become 1/2

CO -> C + 1/2O2 ΔH= 110.5 KJ

the reaction become

PbO + C -> Pb + CO        ΔH= 106.8 KJ

CO          -> C + 1/2O2     ΔH= 110.5 KJ

——————————————–

PbO -> Pb + 1/2 O2  ΔH= 217.3 KJ

Entry Filed under: Thermochemistry