12.2.6 CIA Demonstration: Boiling Water in a Paper Cup

Question 1

CIA Demonstration: Boiling Water in a Paper Cup

Answer 1

• During a phase transition, temperature remains constant.

* Water can be boiled in a paper cup because the paper stays at about 100°C while there is still water present.

Question 2

note

Answer 2

• During a phase transition, temperature remains constant.
• Thus, when ice is melting, the temperature of the mixture of ice and liquid water remain constant at 0°C at one atmosphere. When the ice is gone the temperature will rise with further input of heat.
• Likewise, when water is boiling (changing from liquid to gas) the temperature will stay constant at 100°C (at one
  atmosphere) until all of the liquid disappears.
• Water can be boiled in a paper cup because the paper stays at about 100°C while there is still water in the cup.
• Intuitively, it seems the paper cup should burn when exposed to the flame of a gas burner. It does not because while the water in the cup is in its phase transition from liquid to vapor, the temperature of the paper is held near 100°C by the water next to it.
• The high heat capacity of water allows it to rapidly absorb heat from the paper of the cup, preventing it from burning. Other substances, with lower heat capacities would not keep the cup from burning.