1. Water and steam are both 100 °C when water is boiling, but a burn from steam

Question

1. Water and steam are both 100 °C when water is boiling, but a burn from steam is worse than a burn from the water. Hypothesize why this is true.

2. What happens to the temperature of the water after it starts boiling?

3. Explain why temperature does not change during a phase change. Where does the heat energy go if not into increasing or decreasing temperature?

4.It takes 334 J of heat energy to melt 1 g of ice (this is called the latent heat of fusion). Use this to predict the amount of energy it should take to melt a 12-gram ice cube. Show your work.

Explanation / Answer

1. Because steam contains more heat energy than the boiling water even though both are at the same temperature.
As the water reaches 100 degree Celsius, the phase transition occurs and the temperature remains constant, the added heat is used to convert the liquid phase to the vapor phase. This extra heat is stored in the water vapor
The amount of extra heat energy make the steam more dangerous than the boiled water
2. The temperature of the water remains the same (100 degree Celsius)
3. The heat energy is used to break bonds between the molecules of the substances at the phase transition
4. The amount of energy
Q = m L
Where L is the latent heat of fusion and m is the mass of the substance
The heat energy to melt 12 g of ice is
Q = 12 x 334 J = 4008 J

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