Multiple Choice
In a reaction energy diagram, which part of the diagram represents the change in enthalpy (ΔH) for the reaction?
72
views
8. Thermochemistry
Thermochemical Equations
Multiple Choice
What is the standard enthalpy of formation (ΔH_f^ext{°}) value for CO_2(g) in kJ/mol?
A
0 kJ/mol
B
-110.5 kJ/mol
C
-393.5 kJ/mol
D
+393.5 kJ/mol
Verified step by step guidance1
Understand that the standard enthalpy of formation (\( \Delta H_f^{\circ} \)) of a compound is defined as the enthalpy change when one mole of the compound is formed from its elements in their standard states under standard conditions (usually 1 atm and 25°C).
Recognize that for carbon dioxide gas (\( \text{CO}_2(g) \)), the formation reaction from its elements in their standard states is: \(\n\)\(\n\)\( \text{C (graphite)} + \text{O}_2(g) \rightarrow \text{CO}_2(g) \)
Recall that the standard enthalpy of formation of an element in its standard state (like graphite for carbon or \( \text{O}_2 \) gas for oxygen) is defined as zero. This is why the enthalpy of formation for \( \text{CO}_2(g) \) is not zero.
Use standard thermodynamic tables or reliable data sources to find the value of \( \Delta H_f^{\circ} \) for \( \text{CO}_2(g) \), which is typically given in kJ/mol.
Interpret the sign and magnitude of the value: a negative value indicates that the formation of \( \text{CO}_2(g) \) from its elements releases energy (exothermic process), which is consistent with combustion reactions.
Related Videos
Related Practice
