Given 2 Al2 O3( s) ⟶4 Al(s)+3 O2( g) ΔH^∘=3351.4 kJ (a) What is the standard molar enthalpy o

step 1 So what we have is the thermochemical expression represents the standard enthalpy of decompositi

Given 2 Al2 O3( s) ⟶4 Al(s)+3 O2( g) ΔH^∘=3351.4 kJ (a)...

Given $2 \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s}) \longrightarrow 4 \mathrm{Al}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{~g}) \quad \Delta H^{\circ}=3351.4 \mathrm{~kJ}$ (a) What is the standard molar enthalpy of formation of aluminum oxide? (b) What is $\Delta H^{\circ}$ for the formation of $12.50 \mathrm{~g}$ aluminum oxide?

Given
$2 \mathrm{Al}_{2} \mathrm{O}_{3}(\mathrm{~s}) \longrightarrow 4 \mathrm{Al}(\mathrm{s})+3 \mathrm{O}_{2}(\mathrm{~g}) \quad \Delta H^{\circ}=3351.4 \mathrm{~kJ}$
(a) What is the standard molar enthalpy of formation of aluminum oxide?
(b) What is $\Delta H^{\circ}$ for the formation of $12.50 \mathrm{~g}$ aluminum oxide?

Key Concepts

Standard Enthalpy of Formation

This concept refers to the enthalpy change when exactly one mole of a compound is formed from its constituent elements in their standard states under standard conditions (usually 1 atm pressure and 25°C). It is a foundational idea in thermodynamics and is used to compare the relative stabilities of compounds by measuring how much energy is released or absorbed during formation.

Hess's Law

Hess’s Law states that the total enthalpy change for a reaction is the same regardless of the pathway taken from reactants to products. This principle allows one to calculate unknown enthalpy changes by manipulating known reaction enthalpies, by reversing or scaling reactions as necessary.

Stoichiometry

Stoichiometry involves the quantitative relationships between the amounts of reactants and products in a chemical reaction. It is used to relate the moles of substances involved, ensuring that the proportions specified by the balanced chemical equation are maintained when calculating energy changes or converting between mass and moles.

Mole-to-Mass Conversions

Converting between grams and moles is an essential step in thermodynamic calculations. This process uses the molar mass of a compound to determine the number of moles present in a given mass, allowing one to apply thermochemical data—which are usually expressed on a per mole basis—to practical quantities.

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