Adding Heat and Constant Temperature

[Dina Marchenko 2J]

What does it mean that when you add heat to a system, its overall temperature remains constant? Isn't ice colder than boiling water (ie they have different temperatures)? Or does water as a solid have a uniform temperature, then liquid water has its own uniform temperature, then water vapor has its own uniform temperature?

[Julie_Reyes1B]

I think what Dr. Lavelle was trying to show is that when a phase change occurs, it is possible no temperature change occurs. For example, in labs they add heat really slowly to melt ice to liquid water. The actual act of breaking hydrogen bonds to melt the ice requires energy in the form of heat. The ice will be 0° C, and when it melts to water, there will be a point when the water will also be 0°C. In this case the system is taking in heat while maintaining a constant temperature.

[Caitlyn Tran 2E]

Adding on to previous responses, the temperature is measuring a much larger outside system compared to the small system your reaction may be taking place in. Hence, any changes in temperature of the small system may not heavily impact the environment, which may explain why the temperature of the outside remains unchanged.

Also, in labs, you may conduct a reaction in a test tube placed in a reservoir. The reservoir counteracts any changes in temperature, so the outside temperature remains the same. However, you can calculate the heat given off or absorbed by the reaction by measuring the amount of energy the reservoir needed to put in to maintain a constant temperature.

Hope this helps!