interpret energy level diagram for exothermic & endothermic reaction

1. • The reaction between zinc and
hydrochloric acid to form zinc chloride
and hydrogen gas is exothermic. Energy
Zn (s) + 2HCl (aq)
• When 1 mole of zinc react with 2 mole
of hydrochloric acid to form 1 mole of
zinc chloride and 1 mole of hydrogen ∆ H = -126 kJ
gas, heat released is 126 kJ.
• The total energy of 1 mole of zinc and ZnCl2 (aq) + H2 (g)
2 mol of hydrochloric acid is more than
the total energy of 1 mol of zinc
chloride and 1 mol of hydrogen gas.
The difference in energy is 126 kJ.
• The temperature of the reaction
mixture of zinc and hydrochloric acid
will increase.

2. • The reaction between nitrogen
and oxygen to form nitrogen
dioxide is endothermic. Energy
2NO2 (g)
• When 1 mole of nitrogen react
with 2 mole of oxygen to form 2
mole of nitrogen dioxide, heat ∆ H = +66 kJ
absorbed is 66 kJ.
• The total energy of 2 mole of N2 (g) + 2O2 (g)
nitrogen dioxide is more than the
total energy of 1 mol of nitrogen
chloride and 2 mol of oxygen. The
difference in energy is 66kJ.
• The temperature of the reaction
mixture of zinc and hydrochloric
acid will decrease.