A chemist records the heating curve of an unknown pure substance at 1 atm while…
PHYSICS · Multi-part · CBSE · Physics · Thermal Properties of Matter · Thermal Properties of Matter
Problem
A chemist records the heating curve of an unknown pure substance at 1 atm while supplying heat at a constant rate. The temperature of the sample is measured every 30 s and the following data are obtained (first data point at t=0s):
Time / s 0 30 60 90 120 150 180 210 240 270 300
Temperature / ∘C \,-15 \,-5 5 5 5 25 45 65 65 65 85
Additional information for the substance at 1 atm:
• Molar mass =58.0g mol−1
• Molar enthalpy of fusion ΔHfus=10.8kJ mol−1
• Molar enthalpy of vaporization ΔHvap=32.4kJ mol−1
• The sample mass is 29.0g.
Use the data to analyze the energetic aspects of the phase changes.
(a) Identify the two time intervals during which a phase change is occurring and specify which phase change is occurring in each interval.
(b) For the first phase change you identified, calculate the amount of heat (in kJ) absorbed by the sample during that interval.
(c) For the second phase change, calculate the amount of heat (in kJ) absorbed by the sample.
(d) Using your results from parts (b) and (c), determine which phase change requires the greater energy input per mole and provide a particulate-level explanation for the difference.