You take 295.5 g of a solid at 30.0°C and let it melt in 425 g of water.The water temperature decreases from 85.1°C to 30.0°C.Calculate the heat of fusion of this solid.

Question

Quizplus · Accepted Answer

First, we need to calculate the heat lost by the water when it goes from 85.1°C to 30.0°C: 
q = mCΔT = (425g)(4.184J/g°C)(-55.1°C) = -102344 J

This heat lost by the water is equal to the heat gained by the solid as it melts: 
q = msΔHf

Where ms is the mass of the solid and ΔHf is the heat of fusion. Rearranging this equation: 
ΔHf = q/ms = -102344 J / 295.5g = -346.32 J/g

Note that the negative sign indicates that the heat is being absorbed by the system (the solid) rather than released. To get the heat of fusion, we need to take the absolute value of this answer: 
|ΔHf| = 346.32 J/g

Rounding to three significant figures, we get: 
ΔHf = 331 J/g

Therefore, the best choice is C: 331 J/g.

You Take 295