Answers:
Question 1:
The diagram for gallium will have flat, horizontal lines at <u><em>30 and 2204</em></u><em> </em>°C.
Questoin 2:
The diagram for methane will have a <u><em>diagonal </em></u>line representing the <u><em>liquid phase</em></u> between -183°C and -162°C.
Question 3:
For gold, the boiling point corresponds to the y-value at <u><em>2856</em></u><u> </u>°C of <u><em>the top horizontal line</em></u>
Question 4.
For nitrogen, the line at -210°C will be<u><em> flat</em></u>, which represents <u><em>the change from a solid to a liquid</em></u>
Explanations:
Question 1:
The diagram for gallium will have flat, horizontal lines at <u><em>30 and 2204</em></u><em> </em>°C.
The table shows that the melting point of gallium is 30°C and its boiling point is 2204°C.
<em>Melting point</em> is the temperature at which the substace changes its state from<em> solid to liquid</em>. During that change, <em>the temperature</em> of the substance <em>does not change</em>, because the heat supplied is used to accomplish the phase change. So, the temperature is constant and that means <em>that portion of the diagram is flat</em>.
The same is valid during<em> boiling</em>: the temperature remains constant while the substance is passing<em> from liquid to gas</em> at the boiling point.
Questoin 2:
The diagram for methane will have a <u><em>diagonal </em></u>line representing the <u><em>liquid phase</em></u> between -183°C and -162°C.
Between the <em>melting</em> (-183°C) and<em> boiling</em> (-162°C) points of methane, its temperature will increase more or less linearly, which is represented with a <em>diagonal</em> (slant) <em>line</em> between those points. During this interval the heat is used to <em>increase the temperature</em> and no phase of change happens.
Question 3:
For gold, the boiling point corresponds to the y-value at <u><em>2856</em></u><u> </u>°C of <u><em>the top horizontal line</em></u>
<u><em></em></u>
The table shows that the<em> boiling point</em> of gold is 2,856°C.
In a <em>temperature-vs.-time diagram</em> the<em> temperature is represented on the vertical axis (y-value)</em> and the time is represented on the horizontal axis.
Since, the temperature of the substance does not change during <em>boiling,</em> the line during the time that this change of phase is happening is flat. And since this temperatue is higher than the melting temperature, this is the <em>top horizontal line in the diagram</em>.
Question 4.
For nitrogen, the line at -210°C will be<u><em> flat</em></u>, which represents <u><em>the change from a solid to a liquid</em></u>
<u><em></em></u>
The table shows that the <em>melting point </em>of nitrogen is -210°C, that means that the temperature will remain constant at -210°C while the substance is absorbing heat to pass from solid to liquid.
<u>In conclusion, you must remember that all the phase changes, melting (from solid to liquid), freezing (from liquid to solid), boilng (from liquid to gas), and condensing (from gas to liquid) happens at constant temperature, and so the </u><em><u>temperature - vs. - time diagrams </u></em><u>show flat lines (constant y-values) during those intervals of time.</u>
