Energy release from 75c drop in water temp, 1L?

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Discussion Overview

The discussion centers around the energy released when cooling 1 liter of water from 100°C to 25°C, including inquiries about the significance of this energy release and whether the energy change per degree Celsius is linear across different temperature ranges.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asks how much energy is released in joules when cooling 1 liter of water from 100°C to 25°C and questions if this amount is significant.
  • Another participant suggests that calculating the energy release would be beneficial and questions the meaning of "significant."
  • A participant calculates the energy released as approximately 268,800J and compares this to the energy in AA batteries, expressing surprise at the amount.
  • There is a discussion about whether the heating and cooling of water is linear, with one participant questioning if the energy required to raise the temperature from 20°C to 21°C is the same as from 90°C to 91°C.
  • Another participant responds that for the temperature ranges cited, the specific heat of water can be considered constant, but notes that this is not always the case and mentions the importance of phase changes and latent heat.

Areas of Agreement / Disagreement

Participants express uncertainty about the linearity of heating and cooling and whether the specific heat of water remains constant across different temperatures. The discussion includes competing views on the significance of the energy release and the calculations involved.

Contextual Notes

Some participants reference the specific heat capacity of water and its dependence on temperature, as well as the concept of latent heat, indicating that these factors may complicate the discussion of energy release.

supak111
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Hey everyone can anyone tell me how much energy is released (joules) if you take 1 liter of water at 100C and drop it down to 25C (room temp, reg pressure)? Is it significant amount?

Better even how much energy is released (approximately) for every 1c drop in temp? Is the release in energy linear? Say 90C to 89C vs 50C to 49C, both same amount of energy?
 
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supak111 said:
Hey everyone can anyone tell me how much energy is released (joules) if you take 1 litter of water at 100c and drop it down to 25c (room temp, reg pressure)?
Most people here can, but you will benifit more by working it out for yourself.
http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/spht.html
... answers all your questions.
Is it significant amount?
Dunno - what do you mean by "significant"?

Niggle:
You mean, 1 litre of water at 100C drop to 25C?
A "1 litter" is "one platform for carrying people on", and "100c" is a dollar.
 
Lol. So it basically: 80C x 800g x 4.2J= 268,800J? Or am I not doing this right?

Seeing how a AA battery only has about 10,000J, I would consider that significant ;-). In fact I'm kind of shocked it would take about 27 AA batteries
 
That's right - this is why water plays such a big role in temperature regulation. Though it takes 27 AA batteries to heat the water ... it cools down all by itself.

You can check that it makes sense by considering how long it takes for your kettle to bring a cup of water to boil.
 
Yea this is true. Is the heating and cooling linear? What I mean is does it take same amount to go from 20 to 21C and it does to go for 90 to 91C for example?
 
supak111 said:
Yea this is true. Is the heating and cooling linear? What I mean is does it take same amount to go from 20 to 21C and it does to go for 90 to 91C for example?
In terms of the link I gave you, this question amounts to asking if the specific heat is a constant with temperature... for the temperature ranges you cite, for water, yes. However, this is not generally the case, which is why tables of specific heats also list the temperature where they were measured.

Then there is the case of phase changes - look up "latent heat".
 
Will do and thanks.
 

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