Question

Given the following chemical equation, how many coefficients need to be
changed to make this chemical equation balanced?
In + HNO; - Zn (NO3)2 + H2

Answer 1

To balance the given chemical equation, we need to first identify the reactants and products. The given equation is:

\[ \text{In} + \text{HNO}_3 \rightarrow \text{Zn(NO}_3)_2 + \text{H}_2 \]

Analyzing the species involved:

- **Reactants**: In, HNO₃
- **Products**: Zn(NO₃)₂, H₂

Now let's determine the number of each atom in the reactants and products:

- In: 1 (reactant side)
- H: 1 (in HNO₃, reactant side)
- N: 1 (in HNO₃, reactant side)
- O: 3 (in HNO₃, reactant side)

On the product side we have:

- Zn: 1 (in Zn(NO₃)₂)
- N: 2 (in Zn(NO₃)₂, since there are 2 nitrate ions)
- O: 6 (in Zn(NO₃)₂, 3 oxygen per nitrate multiplied by 2)
- H: 2 (in H₂)

Let's list the atoms again:

**Reactants:**
- In: 1
- H: 1
- N: 1
- O: 3

**Products:**
- Zn: 1
- H: 2
- N: 2
- O: 6

To balance the equation, we can see the need for adjustments.

1. We need 2 nitrogen atoms on the reactant side (currently have only 1), so we will have to double HNO₃:
\[ \text{In} + 2 \text{HNO}_3 \]

2. This gives us:
- H: 2 (since we now have 2 HNO₃)
- N: 2 (2 from the 2 HNO₃)
- O: 6 (2 HNO₃ gives 6 O, which matches the 6 in products).

Now, we rewrite the updated equation:

\[ \text{In} + 2 \text{HNO}_3 \rightarrow \text{Zn(NO}_3)_2 + \text{H}_2 \]

**Balancing:**
- In: 1 on each side
- H: 2 on each side
- N: 2 on each side
- O: 6 on each side
- Zn: Now the zinc should also be included in the reactants since it’s part of the products

The correct balanced equation should be:

\[ \text{Zn} + 2 \text{HNO}_3 \rightarrow \text{Zn(NO}_3)_2 + \text{H}_2 \]

Thus, to balance the original equation with respect to the addition of zinc and adjustment of \( \text{HNO}_3 \):

**Changes made:**
- Coefficient of HNO₃ modified from 1 to 2.
- Added Zn on the reactant side.

In total, **two coefficients** need to be adjusted (change one and add one) to balance the equation.