Given a scientific question, generate a correct answer to it.

Example Input: What third property is different if two boxes have the same volume but one has greater mass?
Example Output: density

Example Input: What states that chemical reactions occur when atoms, ions, or molecules collide?
Example Output: collision theory

Example Input: What kind of process occurs naturally under certain conditions, unlike its opposite, which will not take place unless it is "driven" by the continual input of energy from an external source?
Example Output:
spontaneous process