Fill in the coefficients that will balance the following reaction: (Note: Use 1 as coefficient where appropriate.) NaCl + CaS → Na2S + CaCl2

2NaCl + 1CaS → 1Na2S + 1CaCl2

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

"record the time to complete a chemical reaction" would most likely be part of a lab procedure.