Question

How many kilojoules are required to melt 15g of ice at 0c and raise the temperature of the liquid that forms to 85c?

Answer 1

Answer : The heat required is, 10.3178 KJ

Solution :

The conversions involved in this process are :

$(1):H_2O(s)(0^oC)\rightarrow H_2O(l)(0^oC)\\\\(2):H_2O(l)(0^oC)\rightarrow H_2O(l)(85^oC)$

Now we have to calculate the enthalpy change.

$\Delta H=n\times \Delta H_{fusion}+[m\times c_{p,l}\times (T_{final}-T_{initial})]$

where,

$\Delta H$ = enthalpy change or heat required = ?

m = mass of water = 15 g

$c_{p,l}$ = specific heat of liquid water = $4.18J/g^oC$

n = number of moles of water = $\frac{\text{Mass of water}}{\text{Molar mass of water}}=\frac{15g}{18g/mole}=0.83mole$

$\Delta H_{fusion}$ = enthalpy change for fusion = 6.01 KJ/mole = 6010 J/mole

Now put all the given values in the above expression, we get:

$\Delta H=0.83mole\times 6010J/mole+[15g\times 4.18J/g^oC\times (85-0)^oC]$

$\Delta H=10317.8J=10.3178kJ$     (1 KJ = 1000 J)

Therefore, the enthalpy change is, 10.3178 KJ

Answer 2

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