The continuous stirring in the method of mixtures to determine the specific thermal capacity of a substance ensures

Analyze the question: The method of mixtures determines specific heat capacity by mixing a hot substance with a cooler liquid (usually water in a calorimeter). The question asks what continuous stirring achieves.

Concept: In the method of mixtures, we use the principle:

Heat lost by hot body = Heat gained by cold body (plus calorimeter)

m₁c₁(θ₁ − θ) = m₂c₂(θ − θ₂) + m_c c_c(θ − θ₂)

For this equation to work, we need one final steady temperature θ for the whole mixture. If the liquid were not stirred, the water near the hot solid would be warmer than the water far from it, and the thermometer would read a temperature that does not represent the whole mixture.

Evaluating the options:

• A. Continuous dissipation of heat to the room: Wrong. We want to minimize heat loss (by lagging, using a lid, and so on), not encourage it.
• B. Uniform distribution of thermal energy to all parts of the mixture: Correct. Stirring spreads the heat evenly, so the whole mixture reaches the same temperature and the thermometer reading is accurate.
• C. That the thermal energy is confined to the mixture: Wrong. Confinement is achieved by insulation and a lid, not by stirring.
• D. That there is rapid heat exchange: This is partly true, since stirring speeds up the process. But the main purpose is to make sure the temperature is uniform so that the reading is accurate. Option B describes this better.

Answer: B.

Exam tip: For method of mixtures questions, remember the key ideas: stirring gives uniform temperature, lagging and a lid reduce heat loss, and a quick transfer of the hot solid avoids heat loss to the surroundings. If an option mentions "uniform" or "even" with stirring, it is usually the right one.