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What happens to temperature during a phase change?
remains constant
What is the enthalpy of fusion (ΔH_fus)?
The heat required to melt one mole of a solid at constant temperature.
What is the enthalpy of vaporization (ΔH_vap)?
The heat required to convert one mole of a liquid into a gas at constant temperature.
What happens to energy when ice melts? (energy absorbed or released)
Energy is absorbed to break the hydrogen bonds between water molecules.
What happens to kinetic energy when water is boiling?
It remains constant because all the added energy goes into breaking intermolecular forces.
What is the boiling point of water in Celsius?
100°C.
What type of intermolecular force affects the phase changes of water?
Hydrogen bonding.
What is the mathematical relationship between ΔH_fus and ΔH_solid?
ΔH_fus = -ΔH_solid
What happens to the temperature of water at 100°C when it is boiling?
It remains at 100°C until all the liquid has vaporized.
Which phase change absorbs more energy: melting or vaporization?
Vaporization absorbs more energy.
What is the unit for measuring enthalpy change?
Kilojoules per mole (kJ/mol).
Why does evaporation occur only at the surface of a liquid?
Only surface molecules with enough energy can escape into the gas phase.
Why does the temperature remain constant during phase changes?
All the absorbed energy is used to change the phase, not increase kinetic energy.
How much heat is needed to melt 50.0g of ice at 0°C?
16.7 kJ
Why does diethyl ether (C2H5OC2H5) evaporate faster than water?
It has weaker intermolecular forces
What phase changes occur when a substance loses energy but stays the same chemically?
Condensation or freezing.
