# I'm having a bit of trouble identifying which equation is not balanced. can you help? 2C2H6 + 7O2 -----> 4CO2 + 6H2O (b) C3H8 + 5O2 -----> 3CO2 + 4H2O (c) C6H18 + 10O2...

I'm having a bit of trouble identifying which equation is not balanced.

can you help?

2C2H6 + 7O2 -----> 4CO2 + 6H2O

(b) C3H8 + 5O2 -----> 3CO2 + 4H2O

(c) C6H18 + 10O2 -> 5CO2 + 9H2O + 2CO + C

(d) C5H12 + 8O2 -----> 5CO2 + 6H2O

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### 5 Answers

Hello!

This question is more about math than chemistry: we have to carefully count atoms of each type on both sides of equations. Here we see three types of atoms: C (carbon), H (hydrogen) and O (oxygen). Take into account that index n after atom symbol means that the molecule has n such atoms, and no index means 1 atom. This number must be multiplied with the number of molecules.

**a)** 2C2H6 + 7O2 -----> 4CO2 + 6H2O

C: 2*2 + 0 = 4*1 + 0 , H: 2*6 + 0 = 0 + 6*2, O: 0 + 7*2 = 4*2 + 6*1.

All these equations are true, so equation is **balanced**.

**b)** C3H8 + 5O2 -----> 3CO2 + 4H2O

C: 1*3 + 0 = 3*1 + 0, H: 1*8 + 0 = 0 + 4*2, O: 0 + 5*2 = 3*2 + 4*1.

Again **balanced**.

**c)** C6H18 + 10O2 -----> 5CO2 + 9H2O + 2CO + C.

C: 1*6 + 0 = 5*1 + 0 + 2*1 + 1, or 6 = 8 -- false!

So this equation is **unbalanced**.

(it will be balanced if we omit 1CO and C, check)

**d)** C5H12 + 8O2 -----> 5CO2 + 6H2O

C: 1*5 + 0 = 5*1 + 0, H: 1*12 + 0 = 0 + 6*2, O: 0 + 8*2 = 5*2 + 6*1.**Balanced**.

The answer: c) is unbalanced, a), b), d) are balanced.

Balanced is another word for equal. Are the number of elements on each side of the equation (arrow) equal?

To determine the number of atoms you have to take into account coefficients (numbers in front) and subscripts (numbers below the element). The numbers in front (coefficients) are multiplied throughout the substance. Doing this you will find that equation c is unbalanced because the number of carbons are not equal. On the left side of the arrow (reactants) there are 6 C; on the right side of the arrow (products) there are 8 C. Not equal, therefore not balanced.

In order to understand if the following equations are balanced or not, check to see if there is an equal number of oxygen, hydrogen, etc on both sides. If there is a number outside of the compound, distribute the number to each element.

(a) 2C2H6 + 7O2 -----> 4CO2 + 6H2O

LEFT SIDE

4 C

12 H

14 O

RIGHT SIDE

4 C

8 O + 6 O = 14 O

12 H

BALANCED

(b) C3H8 + 5O2 -----> 3CO2 + 4H2O

LEFT SIDE

3 C

8 H

10 O

RIGHT SIDE

3 C

6 O + 4 O = 10 O

8 H

BALANCED

(c) C6H18 + 10O2 -> 5CO2 + 9H2O + 2CO + C

LEFT SIDE

6 C

18 H

20 O

RIGHT SIDE

5 C +1 C + 1 C = 7 C

10 O + 9 O + 2 O = 21 O

18 H

UNBALANCED

(d) C5H12 + 8O2 -----> 5CO2 + 6H2O

LEFT SIDE

5 C

12 H

16 O

RIGHT SIDE

5 C

10 O + 6 O = 16 O

12 H

BALANCED

For any chemical reaction's equation to be balanced, there should be equal number of atoms of every element involved in that reaction on both sides of equation.

Hence, going by this rule, equation (c) is unbalanced as there are 6 carbon atoms on LHS whereas 8 on RHS.Also, number of oxygen atoms on LHS is 20 while it is 21 on RHS.

Rest three equations are balanced.

According to the law of conservation of mass , the total mass of products must be equal to the total mass of the reactants ( as mass can neither be created nor destroyed ) . This is possible only if the number of atoms of each element is equal on the two sides of the equations.

Balancing of a chemical equation means making the number of atoms of each element equal on the two sides of the equation.

In the balancing of ionic equations , not only the number of atoms of different elements should be same on both sides of the equation but also the total charges on the ions should be same on both sides of the equation. So a balanced ionic equation must satisfy mass balance as well as charge balance.

**As per the question equation C is not balanced.**