In a balanced chemical reaction,
the number of atoms on the left-hand side of the equation = the number of atoms on the right-hand side of the equation.
Multiply by 2 on the left-hand side of the equation gives:
2NaHCO3 (s) → Na2CO3 (s) + H2O (l) + CO2 (g)
All the atoms are balanced on both sides of the equation.
Final Answer:
2NaHCO3 (s) → Na2CO3 (s) + H2O (l) + CO2 (g)