mental energy vs motivation

mental energy and motivation both are nouns.

Word	Noun	Adjective	Verb	Adverb
mental energy	Yes	No	No	No
motivation	Yes	No	No	No

As nouns, motivation is a hypernym of mental energy; that is, motivation is a word with a broader meaning than mental energy:

mental energy: an actuating force or factor
motivation: the psychological feature that arouses an organism to action toward a desired goal; the reason for the action; that which gives purpose and direction to behavior

Other hypernyms of mental energy include motive, need.

mental energy (noun)	motivation (noun)
an actuating force or factor	the psychological feature that arouses an organism to action toward a desired goal; the reason for the action; that which gives purpose and direction to behavior
	the act of motivating; providing incentive
	the condition of being motivated