What does heat capacity (C) measure in thermodynamics?

Heat capacity (C) is defined as the amount of energy required to raise the temperature of a substance by a certain amount, usually by one degree Celsius (or one Kelvin). This concept captures how much thermal energy is absorbed or released by a substance as its temperature changes, making it a central measure in thermodynamics when looking at temperature changes.

When you consider the options, the correct interpretation aligns perfectly with what heat capacity signifies: it quantifies the relationship between the quantity of heat added to a substance and the resulting temperature change. For example, a substance with a high heat capacity can absorb a lot of heat without experiencing a significant increase in temperature, indicating that more energy is required to induce a temperature change in that substance compared to one with a lower heat capacity.

In contrast, the other options touch on different thermodynamic concepts. The change needed to increase the volume of a substance relates more to work done on or by the substance rather than heat transfer and temperature change. Energy change during a phase transition involves latent heat, which is different from the specific heat capacity that focuses primarily on temperature changes at constant volume or pressure. Lastly, the total energy of the system refers to the sum of all forms of energy in the system, including kinetic and potential energy,