The expansion work was calculated in problem 4. The enthalpy change calculated in problem 3 is the enthalpy change for equation (3). In other words, it is the enthalpy change per mole of dinitrogen tetroxide. Since there are now ten moles of the gas reacting, the enthalpy change must also be multiplied by ten. The change in energy is
Note that multiplying the enthalpy change of equation (3) by ten moles and converting J to KJ also gives units appropriate for energy.
(6) Is the reaction in equation (3) endothermic or exothermic?
Since the enthalpy change is positive, the final energy state of the equation is higher than the initial state. The reaction must therefore be endothermic.
