Let 1.00 kg of liquid water at 100∘C be converted to steam at 100∘C by boiling at standard atmospheric pressure (which is 1.00 atm or 1.01 × 105 Pa) in the arrangement as shown. The volume of that water changes from an initial value of 1.00×10−3 m3 as a liquid to 1.671 m3 as steam.
What is the change in the system's internal energy during the process?
Let 1.00 kg of liquid water at 100∘C be converted to steam at 100∘C by boiling at standard atmospheric pressure (which is 1.00 atm or 1.01 × 105 Pa) in the arrangement as shown. The volume of that water changes from an initial value of 1.00×10−3 m3 as a liquid to 1.671 m3 as steam.
What is the change in the system's internal energy during the process?
The correct option is D 2.09mJ
Though from the last problem we have the intuition that the internal energy doesn't change until the temperature of the system varies, that is not the most complete picture.
In this case there is a phase change that takes place. When water turns to steam the water molecules have lesser inter-molecular bonding and each molecule's average kinetic energy goes up. This will result in a higher internal energy for the entire system, which can be calculated using first law -
Q=ΔU+W
where
Q = heat provided = 2256 kJ
W = Work done by gas = 169 kJ.
Eint = (2256 - 169) kJ = 2087 kJ ≃ 20.9 mJ.
Remember thatEint will remain constant for a constant temperature only when there is no phase change.
2.09mJ
Though from the last problem we have the intuition that the internal energy doesn't change until the temperature of the system varies, that is not the most complete picture.
In this case there is a phase change that takes place. When water turns to steam the water molecules have lesser inter-molecular bonding and each molecule's average kinetic energy goes up. This will result in a higher internal energy for the entire system, which can be calculated using first law -
Q=ΔU+W
where
Q = heat provided = 2256 kJ
W = Work done by gas = 169 kJ.
Eint = (2256 - 169) kJ = 2087 kJ ≃ 20.9 mJ.
Remember thatEint will remain constant for a constant temperature only when there is no phase change.
