Trend of specific heat in aqueous solutions:\nAs the solute concentration increases in a water-based solution, the specific heat capacity generally tends to…

Introduction / Context:
Specific heat capacity (cp) is the heat required to raise the temperature of a unit mass by one degree. Water has a notably high specific heat, which is why aqueous solutions often exhibit lower cp values as solutes are added. Understanding this trend is important for heat exchanger design, reactor temperature control, and energy balances in process engineering.

Given Data / Assumptions:

• Base solvent is liquid water, cp ≈ 4.18 kJ/kg·K near ambient conditions.
• Solutes typically have lower cp per unit mass than water (ionic and many molecular solutes).
• No unusual heat capacity anomalies (e.g., very low concentrations where measurement noise dominates).

Concept / Approach:
The mixture cp is a mass-fraction-weighted property, modified by interaction effects. When replacing part of the mass of water (high cp) with solute (often lower cp), the composite specific heat capacity usually decreases. This impacts steam demand, cooling water loads, and transient thermal response of equipment containing brines, syrups, or other concentrated solutions.

Step-by-Step Discussion:

Verification / Alternative check:
Consult cp tables for sodium chloride solutions or sucrose syrups: increasing concentration correlates with lower cp compared to water at the same temperature.

Why Other Options Are Wrong:

• Increase: Opposite to the typical behavior of replacing high-cp water with lower-cp solute.
• Remain unchanged / No predictable trend: Empirical data across many solutes shows a consistent decrease, aside from narrow exceptions.

Common Pitfalls:
Forgetting temperature dependence; assuming ideal linear mixing without acknowledging interaction effects (which usually strengthen the downward trend).

Final Answer:
Decrease