Which Has More Thermal Energy: 150 g Iron Skillet at 100°C or 150 g Water at 100°C?

Understanding Thermal Energy and Heat Capacity

Thermal energy, also known as heat, is the internal energy of a system due to the kinetic energy of its particles. The determination of thermal energy can be approached in several ways. One common method is to use standard enthalpies, a basis for calculating thermal energy at 25°C. However, this does not provide the absolute amount of thermal energy present in a substance, merely the amount of energy needed to change the state of the substance at that temperature.

Different Ways to Determine Thermal Energy

Absolute thermal energy can be defined by integrating the heat capacity from zero Kelvin, incorporating all transitions from zero to the temperature of interest. Unfortunately, experimental conditions at zero Kelvin are virtually impossible to achieve, making this approach impractical in most cases.

Another, more practical method is to use a standard temperature, such as 25°C, and the associated standard enthalpies. For instance, the standard enthalpy for iron is used to determine the thermal energy at this temperature. This method simplifies calculations significantly but still does not provide the exact amount of thermal energy at any given temperature.

Specific Heat Capacity and Thermal Energy Calculation

When comparing 150 g of iron at 100°C to 150 g of water at the same temperature, the specific heat capacities play a crucial role in determining the thermal energy. Specific heat capacity is the amount of heat required to raise the temperature of one gram of a substance by one degree Celsius.

For water, the specific heat capacity is approximately 4.2 J/(g·°C), while for iron, it is about 0.45 J/(g·°C). Given that both substances have the same mass (150 g) and the same temperature (100°C), we can calculate the thermal energy gained during a change in temperature using the specific heat capacity.

Example Calculation

To calculate the thermal energy for each substance, we use the following formula:

Thermal energy (Q) mass (m) × specific heat capacity (c) × change in temperature (ΔT)

For iron: Qiron 150 g × 0.45 J/(g·°C) × 75°C (from 25°C to 100°C) 4,687.5 J

For water: Qwater 150 g × 4.2 J/(g·°C) × 75°C 45,562.5 J

As expected, the water requires significantly more energy to raise its temperature from 25°C to 100°C compared to the iron, despite both starting at the same temperature of 100°C.

Conclusion

While both the iron skillet and the water have the same temperature of 100°C, the amount of thermal energy each possesses is significantly different. The water has more thermal energy due to its higher specific heat capacity. This makes it important to consider not just the mass and temperature of a substance but also its specific heat capacity when discussing thermal energy.

For more in-depth information on heat, refer to the Wikipedia article on Heat - Wikipedia.