3. Two equations below look like they are balanced, and they are, but the coefficients are wrong
nevertheless. In one sentence explain what is wrong with them, and rewrite them so that the
coefficients are correct.
2 Mg(OH)2(s) + 4 HCl(aq) → 2 MgCl2(aq) + 4 H2O(l)
C3H6(g) + 4.5 O2(g) → 3 CO2(g) + 3 H2O(g)
Mg(OH)2(s) + 2 HCl(aq) → MgCl2(aq) + 2 H2O(l)
2C3H6(g) + 9 O2(g) → 6 CO2(g) + 6 H2O(g)
The first equation doesn't have the simplest coefficients. The second equation has a fraction and not whole numbers. By the way, in some situations, especially in thermodynamics, it is permissible to use fractions.
In the first equation, the coefficients of Mg(OH)2 and HCl should be multiplied by 2 to correctly balance the equation:
4 Mg(OH)2(s) + 8 HCl(aq) → 4 MgCl2(aq) + 8 H2O(l).
In the second equation, the coefficient of C3H6 should be multiplied by 2 and the coefficient of O2 should be multiplied by 9/2 (which can be simplified to 4.5 as given in the original equation) to correctly balance the equation:
2 C3H6(g) + 9 O2(g) → 6 CO2(g) + 6 H2O(g).