Question

When producing XY as shown in the equation, the total bond energy of the reactants is 732 kJ/mol and the total bond energy of the products is 1256 kJ/mol.

2X + Y2 --> 2XY
Is this reaction endothermic or exothermic? Why? Explain

Answer 1

Each XY molecule is formed from two X atoms and one Y2 molecule. The bond energy of X-Y is not given in the problem statement, so we cannot calculate it directly. However, we can use the bond energies of the other bonds to estimate it using Hess's law.

According to Hess's law, the total energy change for a reaction is the same whether it occurs in one step or in a series of steps.

We can therefore use the bond energies of the other bonds to estimate the bond energy of X-Y as follows:

The bond energy of X-X is 171 kJ/mol (from a table of bond energies).

The bond energy of Y-Y is 418 kJ/mol (also from a table of bond energies).

To estimate the bond energy of X-Y, we can use the following reaction: X + Y2 → XY + Y (this is the reverse of the reaction we are interested in). The bond energy of Y-Y cancels out, and we are left with:

X + Y2 → XY + Y

(2 X-Y) + (1 Y-Y) - (2 X-X) = ΔH

2 (X-Y) - 1 (Y-Y) - 2 (X-X) = ΔH

2 (X-Y) - 2 (X-X) = ΔH

2 (X-Y) = ΔH + 2 (X-X)

(X-Y) = ΔH/2 + (X-X)

We know that the total bond energy of the products (2XY) is 1256 kJ/mol, so the bond energy of one XY molecule is 628 kJ/mol (1256 kJ/mol divided by 2).

Using the equation we derived above, we can calculate the bond energy of X-Y as follows:

(X-Y) = ΔH/2 + (X-X)

(X-Y) = (628 kJ/mol)/2 + 171 kJ/mol

(X-Y) = 314 kJ/mol + 171 kJ/mol

(X-Y) = 485 kJ/mol

The total bond energy of the products (2XY) is therefore 2 x 485 kJ/mol = 970 kJ/mol.

The difference between the total bond energy of the reactants (732 kJ/mol) and the total bond energy of the products (970 kJ/mol) is:

ΔH = total bond energy of products - total bond energy of reactants

= 970 kJ/mol - 732 kJ/mol

= 238 kJ/mol

Answer 2

Step-by-step explanation:

The reaction can be considered exothermic or endothermic based on the bond energies of reactants and products.

In this reaction, the reactants 2X and Y2 are converted into products 2XY. The total bond energy of the reactants is 732 kJ/mol, which means that it takes 732 kJ of energy to break all the bonds in the reactants.

On the other hand, the total bond energy of the products is 1256 kJ/mol, which means that it takes 1256 kJ of energy to break all the bonds in the products.

If the total bond energy of the products is higher than the total bond energy of the reactants, then the reaction is exothermic, meaning energy is released during the reaction. Conversely, if the total bond energy of the products is lower than the total bond energy of the reactants, then the reaction is endothermic, meaning energy is absorbed during the reaction.

In this case, the total bond energy of the products (1256 kJ/mol) is higher than the total bond energy of the reactants (732 kJ/mol). Therefore, the reaction is exothermic, and energy is released during the reaction.