Question

uC₃H₈(g) + sO₂(g) → d CO₂(g) + e H₂O(l)

For the above balanced equation a, b, d and e are respectively:

1. 1, 2, 3, 4
2. 1, 4, 3, 2
3. 4, 3, 5, 1
4. 1, 5, 3, 4

Answer 1

Correct Answer - Option 4 : 1, 5, 3, 4

Concept:

• The Law of conservation of mass states that matter can neither be created nor destroyed.
• In a chemical reaction, new compounds different from the starting materials are formed.
• In accordance with the law of conservation of mass, thus the number of atoms of each element in the reactant and product side will be same.

So, we need to balance the chemical equation.

Calculation:

To balance a chemical reaction:

• Check the number of atoms before and after the reaction.
• Balance the elements one at a time by adding coefficients before them.
• Change the coefficients as required.
• Never change the subscripts.

Let us balance the elements:

Before	After	Multiply by
C = 3	1	3
H = 8	2	4
O = 2	3	1.5

Thus, the equation becomes:

C3H8(g) + sO2(g) → 3 CO2(g) + 4 H2O(l)

At this stage, carbon and hydrogen are balanced, but oxygen is not balanced yet, so we need to multiply oxygen by 5 on the reactant side.

C3H8(g) + 5O2(g) → 3 CO2(g) + 4 H2O(l)

Now, the equation is balanced.

Hence, the co-efficients u, s, d and e for the reaction uC3H8(g) + sO2(g) → d CO2(g) + e H2O(l) are 1, 5, 3, 4 respectively.