객관식
Given the following chemical reaction: 2H2(g) + O2(g) → 2H2O(l), which of the following best describes how to calculate the enthalpy change (ΔH) for the overall reaction using standard enthalpies of formation?
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8. Thermochemistry
Enthalpy of Formation
객관식
The enthalpy of formation of water is –285.8 kJ/mol. What does this value indicate?
A
The enthalpy of formation of water is positive, indicating an endothermic reaction.
B
The formation of 1 mol of H2O from its elements absorbs 285.8 kJ of energy.
C
The formation of 1 mol of H2O from its elements releases 285.8 kJ of energy.
D
285.8 kJ of energy is required to decompose 1 mol of H2O into its elements.
검증된 단계별 안내1
Understand that the enthalpy of formation (\( \Delta H_f^\circ \)) of a compound is the heat change when 1 mole of the compound is formed from its elements in their standard states.
Note that the given enthalpy of formation for water is \( -285.8 \, \text{kJ/mol} \), where the negative sign indicates the direction of heat flow.
Recognize that a negative enthalpy of formation means the reaction is exothermic, so energy is released when water forms from hydrogen and oxygen.
Interpret the value \( -285.8 \, \text{kJ/mol} \) as the amount of energy released when 1 mole of water is formed from its elements under standard conditions.
Understand that the reverse process, decomposing 1 mole of water into hydrogen and oxygen, would require an input of \( 285.8 \, \text{kJ} \) of energy, making it endothermic.
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