. A 100 g sample of water at 25 oC and 1 atm. of pressure _?_ than 100 g of water that has recently been heated to 100 oC from 0 oC and then cooled to 25 oC at 1 atm. of pressure.

To compare the two samples of water, we need to consider their thermal history and the concept of specific heat capacity. The first sample is a straightforward 100 g of water at 25 °C, while the second sample has undergone a heating and cooling process. This difference in thermal treatment affects the energy content and molecular arrangement of the water molecules.

Understanding Specific Heat Capacity

Specific heat capacity is the amount of heat required to raise the temperature of a unit mass of a substance by one degree Celsius. For water, this value is approximately 4.18 J/g°C. This means that when we heat water from 0 °C to 100 °C, it absorbs a significant amount of energy.

Energy Absorption During Heating

When the second sample of water is heated from 0 °C to 100 °C, it absorbs energy as follows:

• From 0 °C to 25 °C: 100 g × 4.18 J/g°C × 25 °C = 10,450 J
• From 25 °C to 100 °C: 100 g × 4.18 J/g°C × 75 °C = 31,350 J

So, the total energy absorbed while heating the second sample to 100 °C is:

Total Energy = 10,450 J + 31,350 J = 41,800 J

Cooling Down to 25 °C

When this heated water cools back down to 25 °C, it releases the same amount of energy it absorbed during heating, which is 41,800 J. However, the molecular structure of the water molecules may have changed slightly due to the heating process, even though they return to the same temperature.

Comparative Analysis of the Two Samples

Now, let’s compare the two samples:

• The first sample is simply 100 g of water at 25 °C, with no additional energy content.
• The second sample, despite being at the same temperature of 25 °C, has undergone a significant energy exchange during its heating and cooling process.

Implications of Thermal History

Even though both samples are at the same temperature and mass, the second sample has a different thermal history. This means that the second sample may contain more energy in the form of kinetic energy of the water molecules, which can affect properties like density and viscosity, albeit slightly. Additionally, if we were to measure the temperature of the second sample immediately after cooling, it might still exhibit some residual effects from the heating process, such as a slightly different molecular arrangement.

Final Thoughts

In summary, while both samples are 100 g of water at 25 °C, the one that was heated to 100 °C and then cooled has a different thermal history, which can influence its physical properties. Thus, they are not entirely the same, even if they appear identical at first glance. This highlights the importance of considering thermal processes when studying materials.