Is carbon dioxide a beginning or ending substance?

With the process of diffusion, the substances like CO2 and water move in and out of the cell.

If the concentration level of CO2 and water is higher in an external environment than that inside the cell, water and co2 moves inside and in case if their concentration level is low, they move outside.

Explanation:

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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 .