Molecules move in random motion within a liquid. The total internal energy of the liquid depends on all of the following except its?

Analyze the question: We need the property that does NOT affect the internal energy of a liquid.

Concept: The internal energy of a substance is the sum of the kinetic energy (random motion of molecules) and the potential energy (intermolecular forces) of all its molecules. The change in internal energy is linked to heat by:

Q = mcΔθ

where m is mass, c is specific heat capacity, and Δθ is the change in temperature.

Checking each option:

• A. Temperature: Temperature is a measure of the average kinetic energy of the molecules. A higher temperature means more internal energy, so it does affect internal energy.
• B. Mass: More mass means more molecules, so a larger total energy. It does affect internal energy.
• C. Specific heat capacity: This determines how much energy is stored for a given temperature rise (Q = mcΔθ). It relates to how the substance stores energy, so it is connected to internal energy.
• D. Melting point: This is the temperature at which the substance changes from solid to liquid. It is a fixed characteristic of the material and does not determine how much energy the liquid holds at a given state. A liquid's internal energy is not determined by where its melting point is.

Answer: D. Melting point is the one factor the internal energy does not depend on.

Tip: For "internal energy depends on all except..." questions, remember that internal energy depends on the amount of substance (mass), temperature, and the type of substance (specific heat capacity). Fixed reference points like melting or boiling points are not part of it.