AP Chemistry Flashcards: Energy of Phase Changes
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
What happens to the temperature of a pure substance while it is undergoing a phase change?
The temperature of a pure substance remains constant during a phase change.
Card 1 of 10
All Flashcards (10)
What happens to the temperature of a pure substance while it is undergoing a phase change?
The temperature of a pure substance remains constant during a phase change.
Which phase changes require an input of energy, and what is the effect on the system's energy?
Melting and boiling require an energy transfer to the system, which increases the system's energy.
Explain the relationship between the energy of a phase change and its complementary process (e.g., melting and freezing).
The energy absorbed during a phase change is equal in magnitude to the energy released during the complementary phase change.
Which phase changes release energy, and what is the effect on the system's energy?
Freezing and condensation release energy from the system, which decreases the system's energy.
Describe the energy transfer during melting.
During melting, energy must be transferred to the system, which causes the system's total energy to increase.
If melting 2 moles of a substance requires 12 kJ of energy, how much energy is released when 2 moles of that substance freezes?
The energy released during freezing is equal in magnitude to the energy absorbed during melting, so 12 kJ of energy will be released.
A pure liquid is placed in a freezer. As it turns to a solid, its temperature remains constant. What is happening to the energy of the system?
The system is undergoing freezing, which means energy is being released and the system's energy is decreasing.
What two factors determine the amount of heat (q) absorbed or released during a phase transition?
The heat (q) depends on the amount of the substance in moles and the molar enthalpy of the phase transition.
Describe the energy transfer during condensation.
During condensation, energy is released from the system, which causes the system's total energy to decrease.
How does the magnitude of energy absorbed during vaporization compare to the energy released during condensation?
The energy absorbed during vaporization is equal in magnitude to the energy released during condensation.