The beginning of the graph looks almost flat, but the last part started to spike up. What happened between 25 minutes and 30 minutes? Well, it turns out, through careful observation, that at this point, all the ice melted! The ice/water mixture was close to 0°C until the ice was completely melted.
It turns out that the energy added to the mixture was used to melt the ice rather than raise the temperature. In fact, if we extend this graph in both directions, we would get something of this shape:
We call the energy that goes into melting the ice the latent heat of fusion. This energy does not raise the temperature of the ice/water mixture, that's why the graph is flat (zero slope) at that point. The other flat area near the top is when the water boils and we call that the latent heat of vapourization.
Here are the notes:
Latent Heat
The energy it takes to melt or freeze a substance is called the latent heat of fusion, QF
The energy it takes to evaporate or condense a substance is called the latent heat of vaporization, Qv
Specific Latent Heat of Fusion: LF = QF/m
Specific Latent Heat of Vaporization: Lv = Qv/m
- different for every substance
- measured in J/kg
Here are the terms you need to know:
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Here are the different states of matter:
What is the temperature of this water?
Zero degrees! We know this because when ice and water are both present, the temperature must be zero degrees! If it was higher, it'd be all water, if it were colder, it'd be all ice.
Can water be solid, liquid and gas at the same time? Yes! It depends on the pressure. Here's the complicated graph I showed and tried to explain. You will NOT need to know this graph in this course. It's purely for the sake of interest.
You do need to know these example questions I did:
Continue with your textbook homework and remember your lab is due tomorrow!
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