Question

Mid term tomorrow pleaseee help !
Calculate the amount of heat released when 100kg of water freezes at 0 degrees Celcius.

Answer 1

just walk me through the method, i dont know where to start from, please !

Answer 2

Perhaps use the formula
\[E=ml_f\]
If the water is at 0 degree Celsius. If not, add the term mcΔT to the right.

Answer 3

the only formulas we're allowed to use are \[q=mc \Delta t\] and \[\Delta H= |q_{surroundings}|\]

Answer 4

In that case, may I know how you can calculate \(|q_{surroundings}|\)? I mean for the delta t.
If I still remember what I've learnt, during the process of freezing, at 0 degrees Celsius, you can't observe the temperature change of the water, even though there is some energy change. Though.. there is a very high possibility that I'm wrong :|
@apoorvk Can you help??

Answer 5

Well as you know, when a particular substance freezes, some extra energy is released at the particular temperature (freezing point) due to the increase in the inter-molecular attractive forces, (which results in the molecules coming close together, and appearance of the 'solid'-like features). This release of energy is called the "ENthalpy of Fusion" which is synonymous to "Latent Heat of Freezing". It is defined as the energy released per gram of water that freezes.
So for latent heat 'L' and mass 'm', energy released 'E' would follow:

E = mL

We would use this normally but...

Answer 6

@Callisto - exactly what am thinking - how do we find out the temperature change for a non ideal system?

I

Answer 7

is it the opposite of that evaporating ?

Answer 8

evaporating is liquid to gaseous, freezing or fusion refers to only solid-liquid state inter-conversions.

Answer 9

@burhan101 do you know what the differences between latent heat and specific heat are?