Let a, b, c, and d be coefficients in the balanced reaction,
a H₂SnCl₆ + b H₂S → c SnS₂ + d HCl
Count the atoms on both sides and set the amounts equal to each other:
• H : 2a + 2b = d
• Sn : a = c
• Cl : 6a = d
• S : b = 2c
Suppose a = 1. Then
6a = d ⇒ d = 6
2a + 2b = d ⇒ b = (d - 2a)/2 = 2
b = 2c ⇒ c = b/2 = 1
So, the balanced reaction is
1 H₂SnCl₆ + 2 H₂S → 1 SnS₂ + 6 HCl
