Question

Which one of the following chemical equations is balanced? A. 2NaCl + H2SO4 → HCL + NaSO4 B. 2Na + S → 2NaS C. KOH + H2SO4 → KHSO4 + H2O D. NH3 + H2O → 2NH4OH

Answer 1

Answer: C. $KOH +H_2SO_4\rightarrow KHSO_4 +H_2O$

Explanation:  According to the law of conservation of mass, mass can neither be created nor be destroyed, and remains conserved. The mass of products must be same as that of the reactants.

Thus the number of atoms of each element must be same on both sides of the equation so as to keep the mass same and thus balanced chemical equations are written.

a) $2NaCl+H_2SO_4\rightarrow HCl+NaSO_4$

The number of atoms of sodium on product side is 1 and on reactants there are two sodium atoms.

b) $2Na+S\rightarrow 2NaS$

The number of atoms of sulfur product side is 2 and on reactants there is 1 atom of sulfur.

c) $KOH+H_2SO_4\rightarrow KHSO_4+H_2O$

All the atoms are balanced.

d) $NH_3+H_2O\rightarrow 2NH_4OH$

The atoms of nitrogen , hydrogen and oxygen are not balanced.

Answer 2

To determine whether our equations are balanced, we must write the elements on the products side and also the reactants side. If the amount of the elements (coefficients and subscripts) are equal on both sides, we have a balanced equation. 

Lets try (A)

2NaCl + H₂SO₄ → HCl + NaSO₄

Na=2                    Na=1
Cl=2                    Cl=1
H=2                      H=1
Na=2                    Na=1
S=1                      S=1
O=4                     O=4
Most of the elements here are not equal for both sides, therefore, A is not the answer. 

Lets try (B)
2Na + S → 2NaS

Na=2        Na=2
S=1          S=2
This is a wrong answer because S is not equal on both sides. B is a wrong answer. 

Lets try (C)
KOH + H2SO4 → KHSO4 + H2O

K=1                       K=1                  
O= 1                     O=1
H=1                      H=1
H=2                     H=2
S=1                      S=1 
O=4                     O=4

THIS IS A BALANCED EQUATION!!!! ALL ELEMENTS ARE EQUAL ON BOTH SIDES!!!

Since we already know that C is our answer, we have no need to check D. Also, D is incorrect because N has 1 on reactants side, and 2 on the other. Therefore, we automatically know that D is wrong.

FINAL ANSWER: C IS OUR ANSWER, IT IS A BALANCED EQUATION. :)