8.87 Temperatures

[Cam Bear 2F]

"How much heat is required to convert a 42.30g block of ice at -5.042 degrees C into water vapor at 150.35 degrees C?"

I think understand why you have to break it up into different steps based on the graph, but how do you know which temperature to go to. Like for the first step why do you go from -5.042 to 0 degrees C and then for the third step why do you go from 0 to 100 degrees C? Is it always these temperatures for ice to liquid and liquid to gas?

Thanks!!

[Jasmine Botello 2F]

I think it is because 0 degrees is the melting point and 100 degrees is the boiling point and those are like important states.

[Jakob von Morgenland 2C]

Yes, 0 degrees Celsius is the temperature at which ice melts, and 100 degrees Celsius is the temperature at which water vaporizes. At these temperature values, you need to calculate the enthalpy of melting/vaporization and incorporate that into your total enthalpy amount.

[Natalie LeRaybaud 1G]

Yes you would always use these temperature intervals because according to the heat curve 0 degrees is waters melting point and 100 degrees is the boiling point for water. These temperatures are significant because it is right at the point before a phase change occurs. Ex: 0 degrees: solid-> liquid and 100 degrees
liquid->gas and you must calculate the change in energy for each of these steps.

[Cam Bear 2F]

Ok thanks guys! Say it's for something other than water, how are we supposed to know what the melting point and boiling point is?

[Jakob von Morgenland 2C]

It would most likely be given in that scenario.