Question about the chemistry equations

Question

Hello, I've just started learning basic chemistry and I'm confused now. What's the difference between those two? I have a test and only one of them is the right one.

1) NaCl+H2SO4=HCl+NaHSO4

2) NaCl+H2SO4=HCl+Na2SO4

also the same problem goes with:

1) NaOH+CO2=NaHCO3

2) NaOH+CO2=Na2CO3+H2O

Could you explain in detail please. Thank you in advance.

Answer 1

The question does not provide state/phase conditions, and this makes a big difference in how the reaction may or may not proceed. For example, if the NaCl is aqueous, then we have the following:

2NaCl(aq) + H₂SO₄(aq) ==> NO REACTION because you would end up with 2Na⁺(aq) + 2Cl^-(aq) + 2H⁺(aq) + SO₄^2-(aq) and no gas or insoluble product is formed. Since you are just learning chemistry, you would probably be dealing with the following, where NaCl is a solid.

NaCl(s) + H₂SO₄(aq) ==> HCl(g) + NaHSO₄(aq)

For the second problem, again you MUST SHOW STATE symbols. Assuming dilute NaOH(aq)....

NaOH(aq) + CO₂(g) ==> NaHCO₃(aq) + H₂O(l). This can actually be shown as a 2-step reaction:

CO₂(g) + H₂O(l) ==> H₂CO₃(aq)

H₂CO₃(aq) + NaOH(aq) ==> NaHCO₃(aq) + H₂O(l)

(H₂CO₃(aq) is very unstable and if found in water will revert to H₂O + CO₂₎