Energy Required to Change Water into Steam

In summary, water changes into steam through a process called evaporation, where water molecules absorb enough energy to break their bonds and escape as water vapor. The energy required for this process is known as the heat of vaporization, which varies depending on temperature and pressure but averages around 2260 kJ per kilogram of water. Water's high heat of vaporization is due to its strong intermolecular bonds, making it more difficult to break and requiring more energy. The starting temperature of the water also affects the energy required, with higher starting temperatures needing less energy. Pressure also plays a role, with higher pressures requiring more energy and lower pressures requiring less energy, which is why water boils at a lower temperature at higher altitudes.
  • #1
Seinfeld4
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Homework Statement



How much energy is required to change one-quarter of 8.0kg of water at 25 C into steam?

The way I see it, the entirety of the 8.0kg of water must be brought from 25 C to 100 C, then only 2.0kg is changed to steam so...

Specific heat capacity (of water) = 4200 J / kg C
Latent heat of vaporization (of water) = 2.3 * 10^6 J/kg

Q total = (8.0kg) (4200 J / kg C) (100-25) + (2.0kg) (2.3 * 10^6 J/kg)
Q total = 7.12 * 10^6 J

I'm not 100% sure if I'm doing this properly. Does this look correct?
 
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  • #2
That looks correct to me!
 
  • #3
Cool, thanks!
 

1. How does water change into steam?

Water changes into steam through a process known as evaporation. This occurs when the water molecules absorb enough energy to break their bonds and escape into the air as water vapor.

2. What is the energy required to change water into steam?

The energy required to change water into steam is known as the heat of vaporization. It varies depending on the temperature and pressure of the water, but on average, it takes around 2260 kJ of energy to turn one kilogram of water into steam.

3. Why does it take more energy to change water into steam compared to other substances?

Water has a high heat of vaporization because of its strong intermolecular bonds. These bonds must be broken in order for the water molecules to escape into steam, which requires a significant amount of energy.

4. Does the energy required to change water into steam depend on the starting temperature of the water?

Yes, the energy required to change water into steam does depend on the starting temperature of the water. The higher the starting temperature, the less energy is needed to reach the boiling point and turn into steam.

5. How does pressure affect the energy required to change water into steam?

Pressure plays a significant role in the energy required to change water into steam. Higher pressures require more energy to turn water into steam, while lower pressures require less energy. This is why water boils at a lower temperature at higher altitudes, where the air pressure is lower.

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