Question

what is the balanced equation for aqueous zinc chloride and aqueous sodium chromate?
Is it, ZnCl2+NaCrO4-->ZnCrO4+NaCl2
and how do I know if it is reactive or not?
You know it is reactive by one of the following:
1. A gas is formed
2. A solid (insoluble in solvent) is formed.
3. A weak electrolyte is formed.

These are aqueous solutions so 1 is out.
All of these are strong electrolytes so 3 is out.
For 2 you need to know the solubility tables. ZnCrO4 is insoluble so you know a reaction takes place.

For balancing, you must first use the right formula for the materials present or formed.
ZnCl2 + Na2CrO4 ==> ZnCrO4 + 2NaCl.
Note that NaCl2 is not the right formula for sodium chloride and NaCrO4 is not the right formula for sodium chromate.

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