Question

When 15.3 g of sodium nitrate, NaNO3,was dissolved in water in a calorimeter, the temperature fell from 25.00oC to 21.56oC. If the heat capacity of the solution plus the calorimeter is 1071 J/o C, what is the enthalpy change when one mole of NaNO3 dissolves

Answer 1

Answer:

20.468 kilo Joules is the enthalpy change when one mole of sodium nitrate dissolves.

Explanation:

Heat lost by solution ad calorimeter = Q

Heat capacity of solution ad calorimeter = C = 1071 J/°C

Change in temperature = ΔT = 21.56°C - 25.00°C = -3.44°C

$Q=C\times Delta T$

$Q=1071 J/^oC\times (-3.44^oC)=-3,684.24 J$

Heat gained by sodium nitrate = -Q = -(-3,684.24 J)=3,684.24 J

Moles of sodium nitrate = $\frac{15.3 g}{85 g/mol}=0.18 mol$

When 0.18 mole of sodium nitrate was dissolved in water 3,684.24 joulesof heat was absorbed by it.

Then heat absorbed by 1 mole of sodium nitrate :

$\frac{3,684.24 J}{0.18}=20,468 J=20.468 kJ$

1 J = 0.001 kJ

20.468 kilo Joules is the enthalpy change when one mole of sodium nitrate dissolves.