Answer:
2NaCl + 1CaS → 1Na2S + 1CaCl2
Step-by-step explanation:
The reaction in the question is a double-replacement reaction. The general formula is:
BX + CY → CX + BY
Where the cations of two salts exchange anions to produce 2 news products.
To balance the reaction:
NaCl + CaS → Na2S + CaCl2
We can balance as first the Na:
In reactants there is just 1 Na in NaCl but in products there are 2.
To balance Na:
2NaCl + CaS → Na2S + CaCl2
Now, there are 2 Na in reactants and products
There are 2 Cl in reactants and products
There is 1 Ca in both sides
And 1 S in both sides.
The balanced reaction is:
2NaCl + 1CaS → 1Na2S + 1CaCl2