Q 8.67

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William Lan 2l
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Q 8.67

Postby William Lan 2l » Thu Jan 18, 2018 10:06 pm

How do we approach this problem? Especially for a, what are the steps for estimating the enthalpy of formation of H20? Where do we start?

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Re: Q 8.67

Postby miznaakbar » Fri Jan 19, 2018 12:04 am

For this problem, we use bond enthalpies to find the enthalpy of formation of the given compounds in their liquid state. For H2O, I wrote the balanced rxn as H2(g) + (1/2)O2(g) -> H2O(g) and then another phase change rxn to find the enthalpy for the liquid state: H2O(g)->H2O(l). For the first rxn for the formation of H2O, you add the energy required to break 1 H-H bond and to break (1/2) times O-O bond and then subtract the energy required to form 2 O-H bonds. For the phase change, it will take approx -44.0kJ to go from the gas to liquid state. The other parts involve similar steps, hope this helps.

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