In: Chemistry
How much heat (in kJ) is given off when 41.0g of water at 50.0°C is changed to 41.0g of ice at -5.00°C?
The specific heat of water is 4.184 J/g·°C
The specific heat of ice is 2.087 J/g·°C
The heat of fusion of water is 6.02 kJ/mol
1 mol of water is 18.0g
Water
Mass 41 g
T 50 degC
sp heat 4.184 J/g deg
Heat of fusion 6.02 kJ/mol
heat of fusion in J/mol= 6020
Molar mass of water 18 g/mol
Heat of fusion in J /g 108360 J/g
Ice
T is -5 deg C
sp heat =2.087 J/g deg
Calculation of heat
q=C x m x delta T
q Heat in J
C specific heat
m Mass in g
Delta T change in T
There are following transitions in temperature
Delta T
1st (q1) from 50 deg C to 0 deg C -50 deg C
2nd (q2) From 0 deg C to 0 Deg C 0 deg C
3rd (q3) From 0 deg C to -5.0 deg C -5 deg C
Lets calculate q value for all these transitions
q = q1+q2+q3
q1= (41.0 x 4.184 x -50 ) J
-8577.2 J
For q2 we use delta H in J/g
q2 = Delta H x mass of water
q2=(108360 x 41.0) J
=4442760 J
Heat of freezing = - heat of fusion
Therefore q2 has minus sign
q2= -4442760
q3 calculation is based on ice and therefore use the specific heat of ice.
q3=(41.0 x 2.087 x -5 ) J
=-427.835 J
q = -8577.2 - 4442760 -427.835
= -4451765.0 J
So the heat given by 41.0 g water in order to decrease its T from 50 deg C to -5 deg C would be
4451765.0 J