HELP ASAPPP! Most scientists believe that perpetual-motion
devices can never be invented, but people come
up with new ideas for them all the time. Do you
think people should keep trying? Why?

Arock can be broken down into different kinds of substances by physical processes. no chemical reactions are needed to separate different parts of a rock into pure substances. this is because a rock is a(n)

Achange in the number of neutrons in an atom will change an blank . when the number of protons changes in an atom, a new element will form.

Asample of ammonia reacts with oxygen as shown. 4nh3(g) + 5o2(g) 4no(g) + 6h2o(g) what is the limiting reactant if 4.0 g of nh3 react with 8.0 g of oxygen? o2 because it produces only 0.20 mol of no. nh3 because it produces only 0.20 mol of no. o2 because it produces two times less no than nh3. nh3 because it produces three times more no than o2.