H2+(1)/(2) O2 ⟶H2 O ; Δl I=-68.39 kcal K+aq ⟶KOH(aq)+(1)/(2) H2( g) ; Δ/ I=-48 kca 1 KOII+aq ⟶KO

step 1 Hydrogen gas reacts with half molecule of oxygen forming water. Change of endropi is minus 68 .3

H2+(1)/(2) O2 ⟶H2 O ; Δl I=-68.39 kcal K+aq ⟶KOH(aq)+(1)/(2)...

$\mathrm{H}_{2}+\frac{1}{2} \mathrm{O}_{2} \longrightarrow \mathrm{H}_{2} \mathrm{O} ; \Delta l I=-68.39 \mathrm{kcal}$ $\mathrm{K}+\mathrm{aq} \longrightarrow \mathrm{KOH}(\mathrm{aq})+\frac{1}{2} \mathrm{H}_{2}(\mathrm{~g}) ; \Delta / I=-48 \mathrm{kca} 1$ $\mathrm{KOII}+\mathrm{aq} \longrightarrow \mathrm{KOHI}(\mathrm{aq}) ; \Delta H=14 \mathrm{kcal}$ The heat of formation (in kcal) of KOII is (1) $-68.3948-14$ (2) $-68.39-48+14$ (3) $68.39-48+14$ (4) $68.39+48+14$

$\mathrm{H}_{2}+\frac{1}{2} \mathrm{O}_{2} \longrightarrow \mathrm{H}_{2} \mathrm{O} ; \Delta l I=-68.39 \mathrm{kcal}$
$\mathrm{K}+\mathrm{aq} \longrightarrow \mathrm{KOH}(\mathrm{aq})+\frac{1}{2} \mathrm{H}_{2}(\mathrm{~g}) ; \Delta / I=-48 \mathrm{kca} 1$
$\mathrm{KOII}+\mathrm{aq} \longrightarrow \mathrm{KOHI}(\mathrm{aq}) ; \Delta H=14 \mathrm{kcal}$
The heat of formation (in kcal) of KOII is
(1) $-68.3948-14$
(2) $-68.39-48+14$
(3) $68.39-48+14$
(4) $68.39+48+14$

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Key Concepts

Enthalpy of Formation

This concept refers to the heat change that occurs when one mole of a compound is formed from its constituent elements in their standard states. It is a fundamental thermodynamic property used to assess the energy content of a chemical compound relative to its elements.

Hess's Law

Hess's Law states that the total enthalpy change for a chemical reaction is the same, regardless of the pathway taken, because enthalpy is a state function. This principle allows the calculation of unknown reaction enthalpies by algebraically combining known enthalpy changes of related reactions.

Thermochemical Equations

Thermochemical equations represent chemical reactions along with their associated enthalpy changes. These equations can be manipulated—by reversing or scaling reactions—to help in the calculation of overall enthalpy changes for combined processes, as required in energy bookkeeping.

Reaction Enthalpy and Sign Conventions

Understanding the sign conventions for reaction enthalpies is essential; a negative value indicates an exothermic process (release of heat), while a positive value signifies an endothermic process (absorption of heat). This knowledge is crucial when summing enthalpy changes to determine the overall energy change of a reaction.

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