Question

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

Explanation:

Step1: Understand phase - change constants

$\Delta H_{vap}$ is the enthalpy of vaporization (liquid to gas), $\Delta H_{fus}$ is the enthalpy of fusion (solid to liquid), and $\Delta H_{sub}$ is the enthalpy of sublimation (solid to gas). When melted iron freezes, it changes from liquid to solid. The reverse of the enthalpy of fusion is used for this process.

Step2: Determine the correct constant

The heat change for freezing is the negative of the heat of fusion. So, $-\Delta H_{fus}$ is used when a liquid freezes.

Answer:

$-\Delta H_{fus}$