Among the following the number of state variable is ______. Internal energy (U) Volume (V) Heat (q) — Thermodynamics and Thermochemistry Chemistry Question

💡 Solution & Explanation

**Step 1: Identify what a state variable is.** A state variable (or state function) depends only on the initial and final states of a system, not on the path taken. Its value is independent of how the system reached that state. **Step 2: Classify Internal Energy (U).** Internal energy is a state variable because it depends only on the current state of the system (temperature, pressure, composition). ΔU is path-independent. ✓ State variable **Step 3: Classify Volume (V).** Volume is a state variable because it depends only on the current conditions of the system (temperature, pressure, amount of substance). ✓ State variable **Step 4: Classify Heat (q).** Heat is NOT a state variable because it depends on the path taken. The amount of heat absorbed varies depending on whether the process is adiabatic, isothermal, isobaric, etc. ✗ Not a state variable **Step 5: Classify Enthalpy (H).** Enthalpy (H = U + PV) is a state variable because it is defined by state variables (U, P, and V). Its change ΔH is path-independent. ✓ State variable **Step 6: Count the state variables.** State variables: U, V, and H = 3 state variables Non-state variable: q = 1 Therefore, the answer is 3.00.