If a system has 325 kcal of work done to it, and releases 5.00×102 kJ of heat into its surroundings, what is the change in internal energy (Δ or Δ) of the system?

the reaction mixture contains some ammonia, plus a lot of unreacted nitrogen and hydrogen. the mixture is cooled and compressed, causing the ammonia gas to condense into a liquid. the liquefied ammonia is separated and removed. the unreacted nitrogen and hydrogen are then recycled back into the reactor .

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.

oxygen, selenium, tellurium, and polonium.

they're all from the same group as sulfur (group 16).