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Zorluk: ZorLatent Heat and Changes of State

The specific latent heat of vaporization of a pure substance is substantially greater than its specific latent heat of fusion because vaporizing requires completely separating the molecules against intermolecular forces and performing work against external pressure, whereas melting requires only overcoming the long-range order of the crystalline lattice.

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True. The specific latent heat of vaporization is substantially larger than the specific latent heat of fusion because vaporization requires completely overcoming intermolecular cohesive forces to transition molecules into the gas phase, in addition to performing work against atmospheric pressure during expansion, whereas melting only disrupts long-range lattice order while keeping molecular spacing nearly identical.
The statement is true because vaporization involves breaking all intermolecular bonds to create a gas phase and doing external work against atmospheric pressure during large volume expansion, whereas fusion only weakens lattice alignment without significant separation or expansion.

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1
Analyze energy and structural changes during fusion (melting).
Melting breaks long-range crystalline order, but molecules remain in close contact in the liquid state with minimal volume change.
Only a small fraction of intermolecular potential energy is changed, and negligible work is done against external pressure.
2
Analyze energy and structural changes during vaporization (boiling).
Vaporization requires complete separation of molecules against attractive forces to form a gas, accompanied by a large increase in volume.
Energy must be supplied both to overcome intermolecular attractions completely and to perform mechanical work (PΔVP\Delta V) against surrounding atmospheric pressure.
3
Compare the thermodynamic energy requirements (LvL_v vs. LfL_f).
Because full molecular separation and expansion work require far more energy than minor lattice disruption, Lv≫LfL_v \gg L_f.
This confirms the physics reasoning in the statement is true.

Anahtar Kavram

Microscopic and Thermodynamic Basis of Latent Heat of Fusion vs. Vaporization
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Konular

Latent Heat and Changes of State

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