In an exothermic process, the sign of ΔH is what?

In an exothermic process, the sign of ΔH is what?

• A. Positive
• B. Zero
• C. Indeterminate
• D. Negative

Answer: (D)

When heat is released by the system, the enthalpy decreases, so ΔH is negative. In an exothermic process, energy exits as heat to the surroundings, meaning the enthalpy of the products is lower than that of the reactants. Since ΔH = H(products) − H(reactants), this results in ΔH < 0. At constant pressure, ΔH essentially equals the heat exchanged with the surroundings, so the observed heat flow is negative as well. An example is combustion, where the reactants start with higher enthalpy and the reaction releases heat, yielding a negative ΔH.

When heat is released by the system, the enthalpy decreases, so ΔH is negative. In an exothermic process, energy exits as heat to the surroundings, meaning the enthalpy of the products is lower than that of the reactants. Since ΔH = H(products) − H(reactants), this results in ΔH < 0. At constant pressure, ΔH essentially equals the heat exchanged with the surroundings, so the observed heat flow is negative as well. An example is combustion, where the reactants start with higher enthalpy and the reaction releases heat, yielding a negative ΔH.