Question

Calculate the energy released when 24.8 g Na2O reacts in the following reaction.

Answer 1

Answer:

= 48.077 kcal

Explanation:

The balanced equation is :

$Na_{2}O(s)+2HI(g)\rightarrow 2NaI(s)+H_{2}O(l)$

$\Delta H=-120Kcal$

Since the stoichiometric coefficient of Na2O = 1 hence its heat is  

-120 Kcal/mol rather -120 Kcal only.

This means when 1 mole of the Na2O is burned , then 120 kcal of energy is released .

Molar mass of  Na2O = 2(mass of Na) + 1(mass of O)

= 2(22.98)+16

=61.97 gram/mol

Molar mass = mass of the substance in grams present in 1 mole of it.

In 1 mole of Na2O , 61.97 gram of it is present.

Hence

61.97 gram of Na2O = -120 Kcal of heat is released

1 gram of Na2O =

$/frac{-120kcal/mol}{61.9gram/mol}$

So,

24.8 gram of Na2O will produce,

$/frac{-120kcal/mol}{61.9gram/mol}/times 24.8$

= -48.077 kcal of heat

You can also proceed through mole concept:

Calculate number of moles in 24.8 gram Na2O

$Moles=\frac{given\ mass}{Molar\ mass}$

Moles of Na2O = 24.08/61.9 = 0.4007 moles

So these many moles will produces:

0.4007 x 120

=-48.07