Question

If an exothermic reaction produces more heat in an open container than it does in a closed, rigid container, what can you say about the numbers of moles of gases in the reaction? Explain your answer.

Answer 1

We can understand this situation or concept by taking an example. Consider reaction between Zinc metal & HCl acid.

Zn(s) + 2HCl (Conc) --> ZnCl₂ (aq) + H₂(g)

This reaction is exothermic (enthalpy change is positive) and one of the product is in gaseous state.

According to Lechatlier's principle, exothermic reactions will be favored by decreasing reaction temperature and removing one of the product also favors forward reaction.

What is happening in the open container ----- product H₂ gas is expelling from the reaction vessel and also during this process gas molecules are carrying the reaction vessel container heat, heat is dissipating from container, this will enhance the reaction to move forward, equilibrium shifts product side.

What is happening in the closed, rigid container ----- heat is not transferring out and also due to rigidness the gas cannot be taken out, hence equilibrium cannot be shifted towards forward direction.

Moles of gas are increasing during the course of the reaction. So an exothermic reaction produces more heat in an open container than it does in a closed, rigid container because of movement of equilibrium towards forward direction in case of open container.

Hope i have demonstrated the reason behind the question and logical thing.

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