Specific chemistry phase changes question

[Claritynow]

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We all the famed q=mcΔT formula. But when do we use q=n*ΔHphase change?

I understand the processes but seem very close to one another? Any help would be appreciated. Thank you

 

[FeinMS]

when you're undergoing phase change where delta T is 0

 

[jtran7]

so if a question states that an 1g ice cube at -10 degree melts completely and ask you what was the Q that was added to achieve this you have to use (m*c*deltaT) + (m*L)

-the first mcdeltaT is the energy needed to raise the temp of the ice cube to 0 degrees (ice still frozen)
-the second m*L is the energy needed to completely melt the ice (temp of water is still zero, because the energy was used to break some intermolecular bonds to turn it into water)

if a question just states an ice cube at 0 degrees was completely melted how much heat was added you just use m*L