If you turn the heat off of boiling water, it cools down pretty quick, and if you leave ice out, it quickly melts. But once it escapes it’s extreme temperature, it then takes much longer for it to get to room temperature. Why is this? /r/
In: Chemistry
The speed of heat transfer is proportional to the temperature difference between the two area.
The closer it get from room temperature, the longuer it takes to dissipate the same amount of energy, the longuer it take to cool off more
Water as do all things has a specific heat capacity, which is a set amount of energy required to raise (or lower) the temperature for a given volume of water. In general the larger the difference between the temperature of the water and the ambient temperature of the surroundings the quicker the temperature of the water will start to move towards the ambient temperature. Now with ice we have something different again in that we have something called latent heat that is a specific amount of energy required to turn ice a 0 centigrade to water at 0 centigrade, the amount of energy required is substantial and is about the same energy required to raise the same amount of water by 80 centigrade https://youtu.be/18pK7rPtAAk
The rate of heat transfer is directly proportional to the temperature difference the water and it’s surrounding but the energy required to change the water 1 degree is quite constant for liquid water.
The result is that water with a temperature farther away from the surrounding air will change temperature faster.
So if the room is at 25C and you have water at 95 C the difference is 50C.
Then the water cools to 35C the difference is only 10C.
So if it took 1 minute for the water to drop from 95C 94C it will take 50/10=5 times longer to drop from 35C to 34C or 5 minutes.
At 27C the difference is only 2C so a drop to 26C will take 50/2 = 25 times longer or 25 minutes.
Melting ice actually takes quite a long time since it requires 333kj/kg versus 4kj/kg per degree to heat water. So melting ice requires the same energy as to heat 0C water to 333/4=83C.
If you have ice and water in a container all of it will be close to 0C until all ice has melted
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