Lifting the backpack off the floor. Force is being applied in only one direction then (up) which is what constitutes as work. Carrying the box of crayons applies force in two directions (up and forward), which cancel each other out. Work has a vector, which is a quantity containing both direction and magnitude (one, finite direction, not two).
5 atoms of hydrogen will be found in the products becuase the law of conservation of mass states that mass is neither created nor destroyed in chemical reactions.
