Hydrogen bromide breaks down into diatomic hydrogen and bromine in the reaction shown.

Question

2HBr . H2+Br2
The energy of the reactant is 732 kJ/mol, and the energy of the products is 630 kJ/mol. What is the total energy of the reactio? Is the reaction endothermic or exothermic?
102 kJ/mol endothermic
-102 kJ/mol endothermic
102 kJ/mol exothermic
-102 kJ/mol exothermic

Answer 1

To determine the total energy change of the reaction, you need to calculate the difference in energy between the products and the reactants.

The formula for the energy change ($\mathrm{\Delta }H$) is:

$$\mathrm{\Delta }H=\text{Energy of products}-\text{Energy of reactants}$$

Given:

• Energy of reactants (HBr) = 732 kJ/mol
• Energy of products (H2 + Br2) = 630 kJ/mol

Now plug in the values:

$$\mathrm{\Delta }H=630,\text{kJ/mol}-732,\text{kJ/mol}=-102,\text{kJ/mol}$$

This means that the reaction releases energy (negative value), indicating that it is exothermic.

Thus, the total energy of the reaction is $-102,\text{kJ/mol}$ and the reaction is exothermic.

The correct answer is: -102 kJ/mol exothermic.