Question

Phase changes of water

1. is enrgy required for each phase change

2. Can both liguid water and steam exist at 100c

Answer 1

yes, and yes. And both ice and water can exist at 0C

Answer 2

1. An energy change is necessary for each phase change but it need not be added. For example, heat must be added to make water boil (change it from liquid to vapor) but heat is given off when steam condenses to liquid.

2. yes, liquid water and steam (especially if we define steam as water vapor) can co-exist at 100. Water at 100 degrees C has a vapor pressure.