A sound wave is mechanical because it does NOT need a medium.

100mg magnesium reacts with 20ml of 1.0m hcl

Astudent reacts 13 moles of iron with 21 moles of oxygen according to the following equation:

The human eye contains a molecule called 11-cis-retinal that changes shape when struck with light of sufficient energy. the change in shape triggers a series of events that results in an electrical signal being sent to the brain that results in vision. the minimum energy required to change the conformation of 11-cis-retinal within the eye is about 164 kj/mol.