Adding Brine to ice water

[theonlytycrane]

This should lower the freezing temperature of the solution which will start to melt the ice. Will the temperature of the solution decrease? Or will it stay constant at 0 celsius during the phase change of ice to water?

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[BerkReviewTeach]

Think about whether the melting of ice is exothermic or endothermic. That should tell you whether the system is gaining heat energy from the environment (and thereby cooling the surrounding solution down) or releasing heat to the environment (and thereby heating the surrounding solution up). Once you answer the endothermic versus exothermic question, you'll have the information to answer your question here and the tools to answer similar questions elsewhere.

 

[theonlytycrane]

Melting of ice is endothermic as it requires heat to melt. Heat taken in from the surrounding water will melt the ice at it's melting point and during the phase change the temperature of the solution will not change. After the ice has melted, the temperature of the solution will be decreased as heat was taken from the surroundings during this process.

Am I thinking about this correctly?

 

[BerkReviewTeach]

Exactly! The melting of the ice will keep the ice/water interface at o˚C, but the water below the interface can drop to a lower temperature because of the presence of solute. This will likely result in a gradient (assuming it is not stirred), until the ice completely melts, at which time the solution will have a temperature below 0˚C, but above the freezing point of the slightly diluted brine solution.