Complete the following reaction.
CH3CH2Br + KCN → _______

To complete the reaction of \( C_2H_5Br \) (ethyl bromide) with \( KCN \) (potassium cyanide), we can analyze the reaction type involved.

### Step 1: Identify the Reaction Type

The reaction between alkyl halides (like \( C_2H_5Br \)) and \( KCN \) is typically a nucleophilic substitution reaction. In this case, \( CN^- \) (cyanide ion) acts as a nucleophile.

### Step 2: Reaction Mechanism

1. **Nucleophile Attacks**: The cyanide ion \( CN^- \) attacks the carbon atom that is bonded to the bromine atom in ethyl bromide. Since bromine is a good leaving group, it can leave easily.

2. **Formation of the Product**: As the cyanide ion attacks, the bromine atom departs, resulting in the formation of a new bond between the carbon atom and the cyanide ion.

### Step 3: Write the Reaction

The balanced reaction can be represented as:

\[
C_2H_5Br + KCN \rightarrow C_2H_5CN + KBr
\]

### Step 4: Product Identification

The product \( C_2H_5CN \) is called ethyl cyanide (or propionitrile). The \( KBr \) formed is a salt byproduct.

### Conclusion

So the complete reaction is:

\[
C_2H_5Br + KCN \rightarrow C_2H_5CN + KBr
\]

This shows that ethyl bromide reacts with potassium cyanide to form ethyl cyanide and potassium bromide.