Multiple Choice
Which of the following is an endothermic process?
78
views
8. Thermochemistry
Endothermic & Exothermic Reactions
Multiple Choice
Which of the following compounds is formed from its elements by an exothermic reaction at 298 K and 101.3 kPa?
A
N2O (g)
B
NaCl (s)
C
H2O2 (l)
D
NH3 (g)
Verified step by step guidance1
Understand that the question asks which compound is formed from its elements by an exothermic reaction at standard conditions (298 K and 101.3 kPa). This relates to the compound's standard enthalpy of formation (\$\(\Delta\) H_f^\(\circ\)\$).
Recall that the standard enthalpy of formation (\$\(\Delta\) H_f^\(\circ\)\$) is defined as the enthalpy change when one mole of a compound is formed from its elements in their standard states under standard conditions.
Recognize that if \$\(\Delta\) H_f^\(\circ\) < 0\$, the formation reaction releases heat and is exothermic; if \$\(\Delta\) H_f^\(\circ\) > 0\$, the reaction absorbs heat and is endothermic.
Look up or recall the approximate standard enthalpies of formation for each compound: NaCl (s), N2O (g), H2O2 (l), and NH3 (g). Note that NaCl (s) has a strongly negative \$\(\Delta\) H_f^\(\circ\)\$, indicating an exothermic formation.
Conclude that the compound with a negative standard enthalpy of formation (exothermic formation) at 298 K and 101.3 kPa is NaCl (s).
