Phase changes of water
1. is enrgy required for each phase change
2. Can both liguid water and steam exist at 100c
yes, and yes. And both ice and water can exist at 0C
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.
1. Yes, energy is required for each phase change of water. When water changes from one phase to another, such as from solid (ice) to liquid (water) or from liquid to gas (steam), the energy needs to be added or removed to break or form intermolecular bonds between water molecules.
To quantify this energy requirement, we use the concept of heat of transformation, also known as specific heat or enthalpy of fusion (for solid to liquid) and enthalpy of vaporization (for liquid to gas). The heat of fusion represents the energy required to convert a given amount of solid into liquid at a specific temperature, while the heat of vaporization represents the energy needed to convert a specific amount of liquid into gas at a particular temperature.
2. At 100°C, under standard atmospheric pressure (1 atm or 101.3 kPa), both liquid water and steam can coexist. This temperature, known as the boiling point of water, is the temperature at which the vapor pressure within the liquid becomes equal to the atmospheric pressure. At this point, water molecules in the liquid phase gain enough kinetic energy to overcome the intermolecular forces and transition into the gaseous phase.
It's important to note that if the pressure is below 1 atm (such as at higher altitudes), the boiling point of water decreases, and steam can exist at temperatures lower than 100°C. Additionally, if the pressure is above 1 atm, the boiling point increases, and water may remain in the liquid phase even at temperatures above 100°C. This concept is utilized in pressure cookers, where an increase in pressure allows water to reach higher temperatures before boiling.