Question

a scientist needs to calculate the amount of heat released when a sample of melted iron freezes. which constant should be used? δh_fus -δh_fus δh_vap -δh_vap

Explanation:

Step1: Recall Phase Change Enthalpy

The enthalpy of fusion ($\Delta H_{\text{fus}}$) is the heat absorbed when a substance melts (solid to liquid). Freezing is the reverse process (liquid to solid), so the heat released will be the negative of the enthalpy of fusion (since the process is exothermic, heat is released). Vaporization ($\Delta H_{\text{vap}}$) is for liquid to gas, so it's not relevant here.

Step2: Identify the Correct Constant

Since freezing is the reverse of melting, the heat released is $-\Delta H_{\text{fus}}$.

Answer:

$-\Delta H_{\text{fus}}$