If Q = -1500 J and n = 0.5 mol, what is ΔH?

If Q = -1500 J and n = 0.5 mol, what is ΔH?

• A. 3 kJ
• B. -3 kJ
• C. 1.5 kJ
• D. -1.5 kJ

Answer: (A)

Heat flow at constant pressure equals the enthalpy change, and the molar enthalpy change is found by dividing the heat by the amount of substance: ΔH = q/n. Here, the heat exchanged is -1500 J, which is -1.5 kJ, and the amount is 0.5 mol. So ΔH = (-1.5 kJ) / (0.5 mol) = -3 kJ per mole. The negative sign shows the reaction releases heat (exothermic) per mole of substance involved. If you were asked for the total enthalpy change for the 0.5 mol, it would be -1.5 kJ.

Heat flow at constant pressure equals the enthalpy change, and the molar enthalpy change is found by dividing the heat by the amount of substance: ΔH = q/n.

Here, the heat exchanged is -1500 J, which is -1.5 kJ, and the amount is 0.5 mol. So ΔH = (-1.5 kJ) / (0.5 mol) = -3 kJ per mole.

The negative sign shows the reaction releases heat (exothermic) per mole of substance involved. If you were asked for the total enthalpy change for the 0.5 mol, it would be -1.5 kJ.