They are the state symbols in a chemical reaction.
s = solid
l = (pure) liquid
g = gas
aq = aqueous ( water) solution.
H2SO4(aq) + CaI2(aq) -> CaSO4(s) + 2HI(aq)
Al | Al^3+ Zn^2+ | Zn
The ionic equation for the reaction is: Fe^2+(aq) + CO3^2-(aq) -> FeCO3(s) and 2Na^+(aq) + 2Cl^-(aq) -> 2NaCl(aq).
2Na+(aq) + SO42-(aq) + Ca2+(aq) + 2Cl-(aq) CaSO4(s) + 2Na+(aq) + 2Cl-(aq)
The net ionic equation for the reaction between KCl(aq) and Pb(NO3)2(aq) to form KNO3(aq) and PbCl2(s) is: 2K^+(aq) + 2NO3^-(aq) + Pb^2+(aq) + 2Cl^-(aq) -> 2K^+(aq) + 2NO3^-(aq) + PbCl2(s)
If you mean pure substances then:HCl(aq) and NaCl(aq) are not pure substances but solutions. The (aq) means the substance is dissolved in water.HCl(g) and NaCl(s) is are pure substances
If you mean Ca(OH)2(s) --> Ca2+(aq) + 2OH-(aq) this is the equation for the dissolving of calcium hydroxide in water.
Cr(s) Cr3+(aq) Ag+(aq) Ag(s) Cu(s) Cu2+(aq) Sn4+(aq), Sn2+(aq) Pt(s)
SO42-(aq) + Ca2+(aq) ---> CaSO4(s)
Ni(s) | Ni2+(aq) Ag+(aq) | Ag(s)
H2SO4(aq) + CaI2(aq) -> CaSO4(s) + 2HI(aq)
Al | Al^3+ Zn^2+ | Zn
The ionic equation for the reaction is: Fe^2+(aq) + CO3^2-(aq) -> FeCO3(s) and 2Na^+(aq) + 2Cl^-(aq) -> 2NaCl(aq).
Cr(s) | Cr3+(aq) Pb2+(aq) | Pb(s)
2Na+(aq) + SO42-(aq) + Ca2+(aq) + 2Cl-(aq) CaSO4(s) + 2Na+(aq) + 2Cl-(aq)
The reaction "Zn (s) + 2HCl (aq) -- H2 (g) + ZnCl2 (s)" is not a double-displacement reaction. It is a single displacement reaction where Zn displaces H from HCl to form ZnCl2 and H2 gas.
The net ionic equation for the reaction between KCl(aq) and Pb(NO3)2(aq) to form KNO3(aq) and PbCl2(s) is: 2K^+(aq) + 2NO3^-(aq) + Pb^2+(aq) + 2Cl^-(aq) -> 2K^+(aq) + 2NO3^-(aq) + PbCl2(s)