Each of the questions or incomplete statements below is followed by five suggested answers or completions. Select the one that is best in each case.
A thermometer is placed in a test tube containing a melted pure substance. As slow cooling occurs, the thermometer is read at regular intervals until well after the sample has solidified. Which of the following types of graphs is obtained by plotting temperature versus time for this experiment?
Select an Answer
This is a question on states of matter. You must convert the description of the physical phenomenon given in the question to graphical form. When a liquid is cooled slowly, its temperature will decrease with time. Thus, the first portion of a graph depicting this phenomenon must show a decrease when temperature is plotted against time. When a pure liquid substance reaches its fusion (melting) point, continued cooling will release heat with time as the substance solidifies. During this period there is no drop in temperature. After the substance has completely solidified, further cooling will cause an additional drop in temperature. The only graph shown that accurately depicts the events described is choice (B), which is the correct answer.