Three researchers propose conflicting explanations for the Mpemba effect (the observation … — ACT

Three researchers propose conflicting explanations for the Mpemba effect (the observation that warmer water can sometimes freeze faster than colder water).

Researcher 1
The effect is primarily driven by mass loss and cooling due to evaporation. Warmer water evaporates much more rapidly than colder water, which reduces the total mass of the water sample that must be cooled and carries away a significant amount of heat (latent heat of vaporization). This mechanism requires that the container is open to the atmosphere.

Researcher 2
The effect is primarily caused by the expulsion of dissolved gases. Heating water decreases the solubility of dissolved gases (such as $O_2$ and $CO_2$ ), causing them to escape. Water with lower gas concentrations has higher thermal conductivity and higher convection rates, accelerating cooling. This mechanism assumes that heating alters the physical and chemical state of the water prior to cooling.

Researcher 3
The effect is driven by changes in hydrogen bonding. In warm water, stretched hydrogen bonds force the covalent $O-H$ bonds to contract and store energy. As the water cools, these bonds relax and release energy, accelerating heat transfer out of the system. This molecular mechanism does not depend on mass loss or gas expulsion, meaning the effect can occur in completely sealed containers.

Match each of the described experimental scenarios or observations to the researcher(s) whose model predicts or is supported by that outcome.

The Mpemba effect is observed in a hermetically sealed, rigid container that prevents mass loss and gas escape.Researcher 3 only
The Mpemba effect is not observed when using water that has been thoroughly degassed prior to the experiment.Researcher 2 only
The Mpemba effect is not observed in an environment with $100\%$ relative humidity, which prevents net evaporation.Researcher 1 only
The initial heating of water alters its physical or molecular state to enhance heat transfer during the subsequent cooling phase.Researchers 1, 2, and 3

Answer

The correct pairings match: (1) the sealed container scenario with Researcher 3 only; (2) the degassed water scenario with Researcher 2 only; (3) the

100\%

humidity scenario with Researcher 1 only; and (4) the initial heating altering the state of the sample with Researchers 1, 2, and 3.

The correct pairings are determined by evaluating the constraints and mechanisms of each researcher's model: the sealed container prevents the mechanisms of Researchers 1 and 2, matching only Researcher 3; degassing specifically targets the primary variable of Researcher 2's model, matching only Researcher 2; preventing evaporation via

100\%

humidity targets the mechanism of Researcher 1, matching only Researcher 1; and the idea that initial heating alters the water's state prior to cooling is a shared premise of all three models, matching Researchers 1, 2, and 3.

Step-by-Step Solution

Analyze Researcher 1's model requirements.

Requires open containers to allow evaporation and mass loss. Disagrees with sealed containers, agrees with humidity eliminating the effect, and agrees that initial heating alters physical state (reducing mass).

To determine which scenarios align with Researcher 1's mechanism.

Analyze Researcher 2's model requirements.

Requires dissolved gases to escape upon heating. Disagrees with sealed containers (where gas cannot escape), agrees with degassed water eliminating the effect, and agrees that initial heating alters physical/chemical state (removing gases).

To determine which scenarios align with Researcher 2's mechanism.

Analyze Researcher 3's model requirements.

Requires molecular changes (hydrogen and covalent bonding) that occur regardless of container sealing or gas content. Agrees with sealed containers, disagrees with degassed water or humidity eliminating the effect, and agrees that initial heating alters the molecular state (stretching bonds).

To determine which scenarios align with Researcher 3's mechanism.

Synthesize the points of agreement and disagreement across all three models to perform the matching.

The sealed container matches Researcher 3 only; the degassed water matches Researcher 2 only; the humidity matches Researcher 1 only; and the initial heating altering the state is a common point of agreement matched to Researchers 1, 2, and 3.

To complete the matching based on the combined analysis of the three viewpoints.

Key Concept

Identifying points of agreement and disagreement among conflicting scientific hypotheses by analyzing their underlying assumptions, experimental variables, and predicted outcomes.

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