Phase Change

Why does a phase change graph have flat lines?

A phase change graph demonstrates how the temperature is affected by how much energy is added to a substance. For example, in order for an ice cube to melt it has to absorb energy from it's surroundings. As the ice melts it's temperature will, in fact, stay the same (this was seen in an experiment done in class). The flat lines on a phase change graph show that during that period of time there was no change in temperature. The water is absorbing energy which is being converted into potential energy. This potential energy is used to change the water from one state of matter into another (solid - liquid - gas ). The graph shows that there are two types of energy being absorbed: kinetic and potential. The kinetic energy creates a change in temperature and is demonstrated in the sloping lines. When potential energy is absorbed is creates a change in the state of matter. The temperature will stay the same, hence the flat lines. The water will never absorb both kinetic and potential energy at the same time. Observe the graph above.

Calculate Q1, Q2, Q3

M x C x DT = Q

Q1:
394.5g x 4.184J/goC x 0 = 0 J

Q2:
394.5 x 4.184J/goC x 50 = 82529.4

Q3:
 394.5g x 4.184J/goC x 97 = 160107.036 J