Thermochemistry pt 3

Melting: negative ΔH; Freezing: positive ΔH

No enthalpy change occurs during phase changes

Melting: positive ΔH (absorbs heat); Freezing: negative ΔH (releases heat)

Both melting and freezing have positive ΔH

3.01 kJ is released

6.01 kJ is released

12.02 kJ is released

No energy is released

Evaporation (liquid → gas)

Melting (solid → liquid)

Both require the same energy

Sublimation (solid → gas)

The temperature decreases during melting

Energy is released

Energy is absorbed

The solid becomes less dense when melting

The temperature at which liquids evaporate

The energy needed to convert 1 mole of liquid to gas

The energy released during freezing

Only applicable to water

enthalpy of condensation is always greater

enthalpy of condensation= ½ enthalpy of vaporization

They are unrelated

enthalpy of vaporization = -enthalpy of condensation?

Fluorine gas (F₂) – Its weaker forces make it easier to vaporize

Hydrogen sulfide (H₂S) – Its polar bonds create stronger attractions between molecules

Both need the same energy

It depends on the container size

Astatine (the largest halogen atom)

Chlorine (medium-sized atom)

Fluorine (the smallest halogen atom)

All halogens vaporize equally easily

Evaporation happens when a few high-energy particles escape; boiling requires most particles to have enough energy

Boiling produces bubbles; evaporation never does

Evaporation only occurs in sunlight; boiling needs a stove

Evaporation requires more energy than boiling

Divide mass by temperature and add ∆H

Multiply moles of the substance by its molar enthalpy of phase change (∆H)

Use only the substance’s boiling point temperature

Subtract ∆H of products from reactants