Refrigerator appliance with self-adjusting mullion

A refrigerator appliance includes a housing, a mullion, and a biasing element. The housing defines an internal cavity and door frame that accesses the internal cavity. The mullion is disposed within the cavity and divides the cavity into a freezer compartment and a refrigerator compartment. A position of the mullion is adjustable within the cavity such that movement of the mullion away from the freezer compartment and toward the refrigerator compartment increases a volume of the freezer compartment and decreases a volume of the refrigerator compartment, and such that movement of the mullion away from the refrigerator compartment and toward the freezer the compartment decreases the volume of the freezer compartment and increases the volume of the refrigerator compartment. The biasing element is secured to the housing and the mullion. The biasing element is configured to bias the mullion toward the freezer compartment.