Question

For a chemical reaction to occur, the bonds holding the atoms of the reactants must be broken. This requires an input of energy, so breaking bonds is an endothermic process. The atoms of the reactants will then rearrange and form new bonds, creating the products. The formation of bonds in the new products releases energy, so this is an exothermic process.

Look at the reaction below. Decide if bonds must be broken or formed for the reaction to occur.

C2H4+302 -> 2CO2 + 2 H20

Column A
1.
The 4 C-H single bonds.:
The 4 C-H single bonds.
2.
The 4 C=O double bonds.:
The 4 C=O double bonds.
3.
The 3 O=O double bonds.:
The 3 O=O double bonds.
4.
The C=C double bond.:
The C=C double bond.
5.
The 4 O-H single bonds.:
The 4 O-H single bonds.
Column B
a.Bonds must be broken.
b.Bonds must be formed.

Answer 1

To analyze the reaction \( \text{C}_2\text{H}_4 + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 2\text{H}_2\text{O} \), we need to identify which bonds are broken in the reactants and which are formed in the products.

### Reactants
1. **C2H4** (Ethylene):
- Contains **1 C=C double bond**
- Contains **4 C-H single bonds**

2. **O2** (Oxygen):
- Contains **3 O=O double bonds** (since we have 3 O2 molecules)

### Products
1. **CO2** (Carbon dioxide):
- Each molecule contains **2 C=O double bonds**. Therefore, for 2 CO2, we have **4 C=O double bonds** total.

2. **H2O** (Water):
- Each molecule contains **2 O-H single bonds**. Therefore, for 2 H2O, we have **4 O-H single bonds** total.

### Identifying Bonds Broken and Formed
Now we categorize the bonds according to whether they are broken or formed:

**Bonds that must be broken:**
- The **1 C=C double bond** in \( \text{C}_2\text{H}_4 \) must be broken.
- The **4 C-H single bonds** in \( \text{C}_2\text{H}_4 \) must also be broken.
- The **3 O=O double bonds** in \( 3\text{O}_2 \) must be broken.

Total Bonds Broken:
- 1 C=C double bond
- 4 C-H single bonds
- 3 O=O double bonds

**Bonds that must be formed:**
- The reaction produces **4 C=O double bonds** in \( 2\text{CO}_2 \).
- The reaction produces **4 O-H single bonds** in \( 2\text{H}_2\text{O} \).

Total Bonds Formed:
- 4 C=O double bonds
- 4 O-H single bonds

### Summary
Now we assign the necessary designation to each bond type in Column A:

Column A:
1. The **4 C-H single bonds**: a. Bonds must be broken.
2. The **4 C=O double bonds**: b. Bonds must be formed.
3. The **3 O=O double bonds**: a. Bonds must be broken.
4. The **C=C double bond**: a. Bonds must be broken.
5. The **4 O-H single bonds**: b. Bonds must be formed.

### Final Answer
1. a (Bonds must be broken)
2. b (Bonds must be formed)
3. a (Bonds must be broken)
4. a (Bonds must be broken)
5. b (Bonds must be formed)