If Q = 2000 J released in a reaction involving 1 mole, what is ΔH?

If Q = 2000 J released in a reaction involving 1 mole, what is ΔH?

• A. -2 kJ
• B. 2 kJ
• C. -0.2 kJ
• D. 0 kJ

Answer: (A)

The concept here is enthalpy change and the sign of heat flow. If a reaction releases heat, it is exothermic, so ΔH is negative. You’re told 2000 J of heat is released for 1 mole of reaction. Convert to kilojoules: 2000 J = 2 kJ. Since this heat leaves the system, ΔH = -2 kJ per mole. This negative value reflects the heat loss to the surroundings. If the reaction had absorbed heat instead, ΔH would be positive.

The concept here is enthalpy change and the sign of heat flow. If a reaction releases heat, it is exothermic, so ΔH is negative. You’re told 2000 J of heat is released for 1 mole of reaction. Convert to kilojoules: 2000 J = 2 kJ. Since this heat leaves the system, ΔH = -2 kJ per mole. This negative value reflects the heat loss to the surroundings. If the reaction had absorbed heat instead, ΔH would be positive.