Question

When a 7.00 g7.00 g sample of KBrKBr is dissolved in water in a calorimeter that has a total heat capacity of 2.72 kJ⋅K−1,2.72 kJ⋅K−1, the temperature decreases by 0.430 K.0.430 K. Calculate the molar heat of solution of KBr.

Answer 1

Answer : The molar heat of solution of KBr is 19.9 kJ/mol

Explanation :

Mass of KBr = 7.00 g

Molar mass of KBr = 119 g/mole

Heat capacity = 2.72 kJ/K

Change in temperature = 0.430 K

First we have to calculate the moles of KBr.

$\text{ Moles of }KBr=\frac{\text{ Mass of }KBr}{\text{ Molar mass of }KBr}=\frac{7.00g}{119g/mole}=0.0588moles$

Now we have to calculate the heat of the reaction.

$q=c\times \Delta T$

where,

q = amount of heat = ?

$c$ = heat capacity = $2.72kJ/K$

$\Delta T$ = change in temperature = 0.430 K

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

$q=2.72kJ/K\times 0.430K$

$q=1.17kJ$

Now we have to calculate the molar heat of solution of KBr.

$\text{Molar heat of solution of }KBr=\frac{q}{n}$

where,

n = number of moles of KBr

$\text{Molar heat of solution of }KBr=\frac{1.17kJ}{0.0588moles}=19.9kJ/mol$

Therefore, the molar heat of solution of KBr is 19.9 kJ/mol