Explain how the crystals of an igneous rock are used to classify it?

If you burn 10 kilograms of wood in a fire (combustion) what is the weight of the products after the fire has finished burning the wood?

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.

Ineed ! i have no clue how to do this problem.