A pure sample of Substance S is put into an evacuated flask. The flask is then heated steadily and the temperature measured as time passes. The results are graphed below, in the middle (in green).Identical experiments are now run on Substance Y and Substance Z. Substance Y is just like S except that it has a lower enthalpy of vaporization △Hv. Substance Z is just like S except that it has a higher enthalpy of fusion △Hf.Select the graphs below, on the left and right, that show the results you expect for these new experiments.
Question
A pure sample of Substance S is put into an evacuated flask. The flask is then heated steadily and the temperature measured as time passes. The results are graphed below, in the middle (in green).Identical experiments are now run on Substance Y and Substance Z. Substance Y is just like S except that it has a lower enthalpy of vaporization △Hv. Substance Z is just like S except that it has a higher enthalpy of fusion △Hf.Select the graphs below, on the left and right, that show the results you expect for these new experiments.
Solution
The graph for Substance Y, which has a lower enthalpy of vaporization △Hv, would likely show a quicker rise in temperature during the phase change from liquid to gas. This is because less heat is required to vaporize Substance Y compared to Substance S. Therefore, the graph for Substance Y should be the one on the left, where the phase change from liquid to gas occurs at a lower temperature.
On the other hand, Substance Z has a higher enthalpy of fusion △Hf, meaning it requires more heat to change from solid to liquid. Therefore, the graph for Substance Z would likely show a slower rise in temperature during the phase change from solid to liquid. This would be represented by the graph on the right, where the phase change from solid to liquid occurs at a higher temperature.
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