Question

In an isochoric process, which parameter remains constant?

• A. Temperature remains constant
• B. Pressure remains constant
• C. Volume remains constant
• D. Concentration remains constant

Hint:

Break down the word isochoric into its root meaning related to space or volume.

Answer 1

The Correct Option is C

Step 1: Classify this using the standard family of thermodynamic processes named by what they hold fixed: isothermal keeps $T$ constant, isobaric keeps $P$ constant, isochoric keeps $V$ constant, and adiabatic keeps heat exchange $q$ at zero.

Step 2: The prefix chor refers to space or volume (as in the word choric), which immediately identifies isochoric with volume, not temperature, pressure, or concentration.

Step 3: Apply the first law, $\Delta U = q + w$, with $w = -P\Delta V$. Because $\Delta V = 0$ throughout an isochoric change, $w = 0$, so every bit of heat supplied goes directly into changing the internal energy, $\Delta U = q_v$.

Step 4: This is exactly why constant volume calorimetry (a bomb calorimeter) is used to measure $\Delta U$ directly. If pressure or temperature were the fixed quantity instead, this simplification of the first law would not hold.

\[ \boxed{V = \text{constant}} \]