Heat needed to evaporate water

In summary, the task is to find the amount of heat required to fully evaporate the water in a 1m^3 vessel that is initially half filled with water and has a pressure of 2bar. The initial enthalpy is unknown and may depend on whether or not the vessel has a pressure relief valve to maintain the pressure at 2bar. The relevant enthalpies needed for the calculation are the enthalpy of water at 100C, the enthalpy of saturated steam, and the enthalpy of vaporization. The temperature of the water is not given in the question and may need to be determined using steam tables.
  • #1
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Homework Statement



A vessel of 1m^3 volume is half filled with water. The pressure inside the vessel is 2bar.
Steam tables are given

Homework Equations



How much heat is needed to completely evaporate the water?


The Attempt at a Solution



I can find the final enthalpy by finding h(g) at 2 bar. But how do you find the initial enthalpy?
 
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  • #2
Does the vessel have a pressure relief valeve that maintains the pressure at 2 bar? If not, the pressure is going to increase linearly with the volume of water boiled off. This part is easy to calculate. As for your steam tables, I'm not sure exactly what you are looking at (different steam tables have different sets of data and use different forms of presentation). There are 3 relevant enthalpies: the enthalpy of water at 100C, the enthalpy of saturated steam, and the enthalpy of vaporization (the difference between the previous 2 numbers).

Have you written down the question completely, and exactly as it was given to you? If not, please post the question EXACTLY as it was given to you. What is the temperature of the water in the vessel?
 
Last edited:
  • #3
I quoted this question from a thermodynamics past paper. This is all that is given.
It is a short answer question ie. given only couple of lines to answer.
 

What is the definition of heat needed to evaporate water?

Heat needed to evaporate water is the amount of thermal energy required to change water from its liquid state to its gaseous state.

How is heat needed to evaporate water different from boiling point?

Heat needed to evaporate water is the total amount of energy needed for evaporation to occur, while boiling point is the specific temperature at which evaporation occurs.

What factors affect the amount of heat needed to evaporate water?

The amount of heat needed to evaporate water can be affected by factors such as temperature, humidity, surface area, and air pressure.

Is the heat needed to evaporate water consistent for all types of water?

No, the heat needed to evaporate water can vary depending on the type of water, such as fresh water or salt water, as well as impurities and other substances present in the water.

How does the heat needed to evaporate water impact the surrounding environment?

The heat needed to evaporate water can have a significant impact on the surrounding environment, as it contributes to the water cycle and affects the overall temperature and humidity levels in the atmosphere.

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