Question

Why do you need to make an ice water slush mixture (instead of only ice) in order to calibrate your thermometer at 0°c?

Answer 1

An ice water slush mixture is used to calibrate thermometers at 0°C because it guarantees the temperature stays constant due to the thermal equilibrium between the melting ice and water, providing a precise reference for calibration.

Step-by-step explanation:

To calibrate a thermometer at 0°C, it is necessary to use an ice water slush mixture rather than just ice. The reason for this is that the mixture of ice and water will be in thermal equilibrium, ensuring that the temperature remains consistently at 0°C. This equilibrium state occurs because the melting ice absorbs heat without a change in temperature until it completely transitions to liquid water.

The presence of ice ensures that any heat added to the system does not increase the temperature but instead is utilized to change the phase of the ice to water. This phenomenon is why a cup of water with ice cubes remains at 0°C on a hot day and why it is essential for the mixture to have both ice and liquid water to create an accurate calibration point for the thermometer.

Answer 2

You want an ice water slush because you want a constant repeatable temperature to calibrate your thermometer. If you only had ice, it's possible for the ice to colder than the freezing point of water. The only real limit to how cold you could have the ice is absolute zero (-273 degrees C). So measuring the temperature of ice isn't a reliable reference. On the other side, if you only had water, it could be any temperature between 0°C and 100°C. Once again, not a reliable reference. But if you have a ice water slush, the ice is undergoing a phase change from solid to liquid and the temperature of the slush will remain constant as long as there's still ice melting. And for water, that phase change from solid to liquid occurs at 0°C, so it is a reliable reference you can use to calibrate your thermometer.