IB Physics Higher Level (HL) Practice Exam

Specific latent heat refers to the amount of energy required to change the phase of a unit mass of a substance without changing its temperature. This concept is crucial when understanding phase transitions such as melting, boiling, or sublimation.

When a material undergoes a phase change, like ice melting into water, the energy supplied does not increase the temperature but instead is used to break the molecular bonds holding the solid structure together. Therefore, the specific latent heat is expressed in joules per kilogram (J/kg) and is unique to each substance depending on the phase transition type—latent heat of fusion for melting and latent heat of vaporization for boiling.

In comparison, the other options do not accurately represent the concept of specific latent heat. For instance, temperature change of a heated object (first choice) refers to sensible heat, not latent heat. The total energy of a gas at constant pressure (third choice) pertains to thermodynamic principles but isn't related to phase changes. Finally, the work done by a gas expanding in a vacuum (fourth choice) is about mechanical work in a thermodynamic context rather than energy absorbed or released during a phase transition. Thus, the correct understanding of specific latent heat is encapsulated by the option provided.