Many homeowners treat their lawns with caco3(s) to reduce the acidity of the soil. write a net ionic equation for the reaction of caco3(s) with a strong acid.

The reaction of acid, assuming HCl and calcium carbonate always produces a gas. The reaction is as follows:
2 HCl + CaCO3 --> CaCl2 + H2CO3 
H2CO3, carbonic acid, is a weak acid that is unstable in water solutions at high concentrations. As such, it decomposes: 
H2CO3 --> H2O + CO2 
Then, 
2 HCl + CaCO3 --> CaCl2 + H2O + CO2 
The total ionic equation looks as follows: 
2H+(aq) + 2 Cl-(aq) + CaCO3(s) --> Ca+2(aq) + 2 Cl-(aq) + H2O(l) + CO2(g) 
Clearly, Cl- is a spectator ion as it is unchanged in the reaction. The net ionic reaction looks as follows: 
2 H+(aq) + CaCO3(s) --> Ca+2(aq) + H2O(l) + CO2(g)