How to find Qtotal

[Emily Ngo 1E]

Hi,
For textbook problem 4C.11, how do we know what that the value for c in qfusion is 334.0 J/g. I couldn't find this value anywhere. And how do we know to use the specific heat of water and not ice. Finally, after calculating qwater and qfusion, do we add the values to find how much heat is needed in total?

[Emiliano Olivo Cauberghs]

Hi,
For this problem, you first need to find the amount of heat required to melt the ice before finding the amount of heat to raise the water temperature to 20*C.
1) For ΔH (melting ice) you need to find the value for ΔH(fusion) which is found in table 4C.1.
To find the heat needed try using the formula ΔH = (mass)/(molecular weight) * ΔH(fusion).

2)To find the necessary amount of heat to raise the heat to 20*C find the value of heat capacity for water (table.4A.2) and use the formula q=mc∆t: q(heat transfer)=m(mass)c(heat capacity of material)∆t(temperature change T2-T1). The heat capacity (c) for liquid water is 4.187J/C/g and not 334.0J*g.


Yes, you must add the values found in both equations to find the total amount of heat needed.

Hope this helped!

[Mandy Mg 2J]

The reason why you could not find the value 334 J/g was because the table 4C.1 provides you the value for ΔH(fusion) of water in kJ*mol^-1. So adding onto the previous reply, that is why you have to divide the ΔH(fusion) of water by water's molecular weight. And to get your answer in J, simply convert kJ to J.