冰的latent heat

Q1. 咁系唔系20粒冰比10粒冰融解的時間長D?因為多d冰?

A: In theory, each cube of ice absorbs heat from the surroundings independently. The time of each ice cube to melt completely is thus the same, as you cannot differentiate one cube from the other. Therefore, the two cups of ice would all melt within the same time interval.

The above argument is only true if all ice cubes are placed separated from one another. But in reality, this may not be so. As the ice cubes may stack together, thus reducing their surface area in contact with the air. This in turn reduces the rate of heat flow from the ambient air towards the ice cubes. Hence, the cup with more ice cubes takes a bit longer time than the one with less ice cubes, but surely would not take twice as long.

This is the reason why crushed ice (碎冰) melts much faster than ice cubes even if the two have the same mass. It is simply because the former has a larger contact area with the air, thus enabling a much larger flow of heat.

Q2.兩個杯中的冰融解時,溫度是不變? 至到冰完全融解成0度的水,再吸室溫的熱,溫度就會上升?

A: Yes, it is true.
Thermal equilibrium between the melting ice and the water is always maintained during the melting process (process of change of state). As such, the temperature of the mixture doesn't change.

(1)E=ml latent heat公式
(2)E=Pt 功率公式
.'.Pt=ml
根據上述情況 假設1粒冰的mass=m
<>即係常數的意思
一樣係室溫 冰又一樣溫度 基於溫差一樣的關係 2杯冰升溫的速度亦一樣 所以 <P>
每粒冰mass 一樣 所以<m>
一樣都係冰 所以 <l>
10粒冰的情況:<P>(t1)=10<m><l>
20粒冰的情況:<P>(t2)=20<m><l>
比較兩條式 2(t1)=(t2) 那就是20粒冰理論上比10粒冰需要多一倍的時間溶解
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固體:分子密度大 = 分子間距離小
液體:分子密度中 = 分子間距離中
氣體:分子密度小 = 分子間距離大
係轉形態的時候變化的只是分子間距離變大/小 , 由於動能不變 ,其溫度亦不變。
而完全轉形態的物質 倘若再吸熱便會增加分子動能 從而增加溫度