Phase Changes and Energy Calculations Flashcards
Students will be able to explain the energy changes that occur during phase transitions (melting, freezing, vaporization, condensation, sublimation, and deposition) and apply energy calculations to determine the heat required for a substance to undergo a phase change. This includes understanding and using key concepts such as heat of fusion, heat of vaporization, and the relationship between temperature, energy, and molecular structure during phase changes.
100°C at 1 atm
The boiling point of water at standard atmospheric pressure (1 atmosphere) is 100°C, where the vapor pressure of water equals the external pressure.
Explain why the temperature of a substance remains constant during a phase change, even though heat is being added or removed.
During a phase change, the added energy is used to overcome intermolecular forces rather than increasing the kinetic energy of the molecules. This is why the temperature remains constant.
For example, when ice melts, the energy goes into breaking hydrogen bonds between water molecules, not raising the temperature.
How much energy is required to convert 250 grams of ice at 0°C into water at 0°C? The heat of fusion for ice is 334 J/g.
Energy = mass × heat of fusion = 250 g × 334 J/g = 83,500 J
The energy required to convert a solid to a liquid at its melting point is calculated using the heat of fusion, which represents the energy needed to break the intermolecular forces in the solid without raising its temperature. In this case, multiplying the mass of ice by the heat of fusion gives the total energy needed to convert 250 grams of ice at 0°C into water at the same temperature.
Explain why steam at 100°C can cause more severe burns than boiling water at 100°C, even though both are at the same temperature.
Steam contains more energy than boiling water at the same temperature because it carries the latent heat of vaporization. When steam condenses on the skin, it releases this additional energy, causing more severe burns.
The latent heat of vaporization is the extra energy required to convert liquid water into steam, which is released when steam condenses
