# A simple question about the direction of a chemical reaction

I do not know much about Chemistry and whatever I knew has become rusty. I have a very simple query. I take a beaker containing pure $$\ce{H2SO4}$$ solution and immerse a rod of pure $$\rm Zn$$ into it. Now, the $$\rm Zn$$ will react with $$\ce{H2SO4}$$ to form $$\rm ZnSO_4$$ and hydrogen gas. $$\ce{H2SO4(aq) + Zn(s) -> ZnSO4(aq) + H2(g)}$$ Why does not the reaction spontaneously reverse once again forming pure $$\rm Zn$$ and $$\ce{H2SO4}$$ molecules?

$$\ce{H2SO4(aq) + Zn(s) <- ZnSO4(aq) + H2(g) ?}$$

• Not quite right, the reaction forms hydrogen gas which bubbles off making the reaction irreversible. – Waylander Mar 21 at 12:50
• Imagine a crowded bus during rush hour. Some people board the bus, others get off the bus. Why don't they spontaneously reverse? Well, sometimes they do, but most would eventually get where they want to be. Same thing here. – Ivan Neretin Mar 21 at 12:51
• Dear @Waylander, I am afraid that logic "the reaction forms hydrogen gas which bubbles off making the reaction irreversible" is not correct. Assume we conduct this reaction at 10,000 psi; at this pressure we will not see any bubbles of H2, can we prevent zinc from dissolving in sulfuric acid or reverse this reaction? Most likely not. The formation of hydrogen is highly favored thermodynamically and its equilibrium constant (if it exists) must be extremely large. – M. Farooq Mar 21 at 14:15
• @M.Farooq The OP asked for a simple explanation without jargon. Feel free to provide a full answer to the question – Waylander Mar 21 at 15:44
• M.Farooq i'll have to agree. Zn2+ will not spontaneously return to metallic state. Hydrogen, even if contained in solution, will not change anything. @Waylander your statement is certainly not a simplification! – William R. Ebenezer Mar 21 at 17:49