Examples of predicting the direction of energy change
In a limited number of cases it is possible to predict from the equation for the reaction whether it will be exothermic or endothermic.
Separating particles that have an attraction for one another is endothermic.
Bringing particles that have an attraction for one another closer together is exothermic.
Processes are endothermic in one direction and exothermic in the opposite direction.
Separation of charge requires energy and is endothermic.
Neutralizing charge or dispersing charge over a bigger volume releases energy and is exothermic.
Separating particles that have an attraction for one another is endothermic.
Bringing particles that have an attraction for one another closer together is exothermic.
Processes are endothermic in one direction and exothermic in the opposite direction.
Thus the phase changes below are endothermic in the forward direction as interparticle forces are being disrupted. They are exothermic in the reverse direction as the particles are being brought closer together.
| solid | endothermic exothermic | liquid | endothermic exothermic | gas |
Separation of charge requires energy and is endothermic.
Neutralizing charge or dispersing charge over a bigger volume releases energy and is exothermic.
- First ionization energy:
Na(g)
Na+(g) + e– endothermic
- Lattice energy:
Na+(g) + Cl–(g) NaCl(s) exothermic
- Hydration energy:
Na+(g) + 6H2O Na(H2O)6+ exothermic