Part A For which of the following reactions is ? H ?rxn equal to ? H ?f of the p

Question

Part A For which of the following reactions is ?H?rxn equal to ?H?f of the product(s)? Check all that apply.

Li(s)+12F2(l)?LiF(s)

S(s)+O2(g)?SO2(g)

SO3(g)?12O2(g)+SO2(g)

SO(g)+12O2(g)?SO2(g)

Li(s)+12F2(g)?LiF(s)

2Li(s)+F2(g)?2LiF(s)

Part B The combustion of pentane, C5H12, occurs via the reaction C5H12(g)+8O2(g)?5CO2(g)+6H2O(g) with heat of formation values given by the following table: Calculate the enthalpy for the combustion of pentane. Express your answer to four significant figures and include the appropriate units. ?H?rxn =___value___ ____units___

Explanation / Answer

Part A

?Hrxn=??vp?H?f(products)???vr?H?f(reactants)

?Hrxn=??vp?H?f(products) means ??vr?H?f(reactants) should be zero

All elements in their standard states have a standard enthalpy of formation of zero, as there is no change involved in their formation.

So we need to check the reactants of each reaction whether they are in their standard states or not.

if they are in standard state then their ?Hrxn=??vp?H?f(products)

S(s)+O2(g)?SO2(g)

Li(s)+12F2(g)?LiF(s)

2Li(s)+F2(g)?2LiF(s) these are the reactions having reactants in their standard state so their ?Hrxn=??vp?H?f(products)

Part B

C5H12(g)+8O2(g)---->5CO2(g)+6H2O(g)

?Hrxn=??vp?H?f(products)???vr?H?f(reactants)

        =5x(-393.5)+6(-241.8)-(-119.9-8(0))=-3298.4 kJ/mol

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