What Happens to Water Temperature and State After Heating for 25 Minutes?

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Discussion Overview

The discussion revolves around the heating of water in a tank using a heater with a specified power output. Participants explore the final temperature and state of the water after being heated for 25 minutes, considering the principles of thermodynamics and heat transfer.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation

Main Points Raised

  • One participant presents a proposed final state of the water as a combination of liquid and vapor at 100°C after heating.
  • Another participant emphasizes the importance of understanding the physical situation, suggesting that heating water may lead to evaporation.
  • A participant mentions the formula Q=mctheta and expresses uncertainty about its application in this context.
  • Further questions are posed regarding the energy added by the heater over the heating period and the energy required to raise the temperature of the water and to vaporize it.
  • Participants discuss the specific heat capacities of water and vapor, as well as the latent heat of vaporization, indicating these are relevant to the calculations needed.

Areas of Agreement / Disagreement

Participants generally agree on the need to calculate the energy added to the water and the energy required for heating and phase changes. However, there is no consensus on the final temperature and state of the water, as the discussion remains exploratory and unresolved.

Contextual Notes

Participants have not yet provided specific calculations or assumptions regarding the energy transfer, and the discussion includes various steps that remain unresolved, such as the total energy added and the calculations for temperature change and phase change.

Who May Find This Useful

This discussion may be useful for students or individuals interested in thermodynamics, heat transfer, and practical applications of physics in heating processes.

Lennonlim123
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A heater so P=500Js^-1,heats up a tank of water of 200ml from 25°C for 25 minutes. What is the final form(solid ,liquid or gas)and the final temperature of the water?
The answer:
Final form : Liquid+vapour
Final temperature: 100°C

I have no idea how to do this!
Plz help!
 
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Welcome to PhysicsForums, Lennonlim123.

Start by understanding the physical situation. Even without looking at the answer, do you see that you are heating water, maybe until some or all of it evaporates?

Do you know how to figure out how much water heats from adding a given amount of energy?
 
I only know Q=mctheta
But how to apply it here?
Wait, I forgot.
The latent heat of vapourise is 2x10^6
The heat capacity of water is 4200
Heat capacity of vapour is 2100
 
Hi Lennonlim123. Welcome to PF!

Generally, you have to follow the rules and tell us what you have tried first. I will assume you don't know where to start. To get a start, answer these questions:

How much energy does the heater add to the water in 25 min.? (hint: you are given the amount of energy is added to the water each second).
How much energy does it take to raise a kg of water one degree C.? How much energy does it take to raise .2kg one degree C?
How much energy does it take to raise .2 kg of water to the boiling point?
How much energy does it take to vaporize one kg of water at that boiling point? How much for .2 kg of water?

(Note: assume the tank is at atmospheric pressure).

AM
 
Lennonlim123 said:
I only know Q=mctheta
I usually see that written as Q=mc∆T
It says that the the amount of heat (Q) added to a body equals the product of the mass (m), the heat capacity (c) and the change of temperature (∆T)

That let's you see where Andrew Mason's first leading question comes in:
How much energy does the heater add to the water in 25 min.? (hint: you are given the amount of energy is added to the water each second).

The answer to that will give you the value to substitute for Q (assuming all the heat goes into the water and stays there until the water boils).
 

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