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Why would the amount of energy required to increase the temperature of a defined mass of water depend on the temperature? This goes against the idea of specific
by bonsai_spool 5mo ago
Why would the amount of energy required to increase the temperature of a defined mass of water depend on the temperature? This goes against the idea of specific heat
(editing to add - I didn't realize that water's specific heat has a temperature dependence and changes around 5% over reasonable indoor temperatures
https://www.engineeringtoolbox.com/specific-heat-capacity-water-d_660.html https://www.engineeringtoolbox.com/specific-heat-capacity-wa...
)
- actionfromafar 5mo agoPhase change?
- kgwgk 5mo agoNo, it doesn't go against the idea of specific heat. You may be thinking of ideal gases and even then specific heat may or may not be constant: https://en.wikipedia.org/wiki/Perfect_gas https://en.wikipedia.org/wiki/Perfect_gas
- bonsai_spool 5mo agoA specific heat is the amount of energy needed to raise a defined mass of a substance by a defined temperature. What does that have to do with a perfect gas?
- Tade0 5mo agoThe ideal gas model assumes point particles with no interparticle interactions, while all the interesting stuff with regards to all kinds of specific heat happens due to these things in... particular.
- kgwgk 5mo agoThe question was > Why would the amount of energy required to increase the temperature of a defined mass of water depend on the temperature? and the answer is that it does, except if you have a very restrictive model where it doesn't. (Edit: I see there was an edit to the previous comment, I had missed that.)
- bonsai_spool 5mo agoYes, I wrote both comments. Why does water relate to the ideal gas law?
- kgwgk 5mo agoIt doesn't. Your initial assumption that the heat capacity is a thing that doesn't depend on temperature did (because it may apply to ideal gases as opposed to water where it just doesn't stay constant as you noticed later).
- defrost 5mo agoTraditionally it's not a "mass" of water, it's a pound (unqualified) of water. There's an issue right there and one that cracks the door open to "how is pound of water created". Leading into (depending on path to above) the issue of density of water, while famously and often described as incompressible, water reaches max density at 4 C, 3.99 degrees (Kelvin or Celsius) above water's triple point.
- PowerElectronix 5mo agoSpecific heat usually varies with the temperature itself.
- willis936 5mo agoThey're not saying the rate varies but the starting point. Going from 30C to 100C takes less energy than going from 20C to 100C even if specific heat remains physical. Both might get labeled a BTU.
- stavros 5mo agoThey specifically said "one degree Fahrenheit", so the GP's question was "why does going from 30 F to 31 F take a different amount of energy than going from 20 F to 21 F?".
- ChiperSoft 5mo agoWell in the later scenario the water would be frozen and conduct heat within the volume poorly, so applying heat would result in a phase change at the contact point. Latent heat transfer is then going to complicate things.
- stavros 5mo agoIt doesn't matter how well it conducts the heat, since you measure the amount the energy you apply to it (after losses).
- simonebrunozzi 5mo agoSee water's triple point.