Spontaneity

Spontaneous process: a process that does occur naturally under a specific set of conditions
- A spontaneous process will “just happen.”
- A spontaneous process occurs naturally at a given set of conditions, without outside forces.
Nonspontaneous process: a process that does not occur naturally under a specific set of conditions

It is important to not confuse spontaneous with fast.
If a reaction is spontaneous in one direction, it will be nonspontaneous in the reverse direction under the same conditions.
A nonspontaneous reaction is still possible with the continual input of energy.
Many spontaneous processes proceed with a decrease in energy.
Recall that exothermic reactions also proceed with a decrease in energy.
- Spontaneous reactions are often exothermic, but not always.
Ice melting is ENDOTHERMIC, but under certain conditions, it IS spontaneous.

When the valve opens, the gas spontaneously expands to fill both containers.
With an ideal gas, this process results in no change in energy.
Two objects at different temperature are placed in contact.
Heat spontaneously flows from the hotter object to the colder object.
But overall, there is no change in energy.
It appears that greater, more uniform dispersal of matter and energy can also be the driving force of a spontaneous process.