Complete and balance the equation: C4H10 + Cl2 → HCl (ultraviolet light) - Leaving Cert Chemistry - Question i - 2009

To balance the reaction between butane (C4H10) and chlorine (Cl2) under ultraviolet light, we start with the equation:

C4H10 + Cl2 → x C4H9Cl + y HCl

Step 1: Determine the Products

• The reaction of alkanes with chlorine typically results in the formation of alkyl halides and hydrogen halides. Thus, we expect products such as butyl chloride (C4H9Cl) and hydrochloric acid (HCl).

Step 2: Write the Unbalanced Equation

• The unbalanced equation can be represented as:

C4H10 + Cl2 → C4H9Cl + HCl

Step 3: Count Atoms of Each Element

• On the left, we have:

  • C: 4 (from C4H10)
  • H: 10 (from C4H10)
  • Cl: 2 (from Cl2)

• On the right, we have:

  • C: 4 (from C4H9Cl)
  • H: 1 (from HCl) + 1 (from every HCl produced) = y
  • Cl: 1 (from C4H9Cl) + 1 (from HCl) = y + 1

Step 4: Balance the Chlorine and Hydrogen Atoms

• Set up the equations:

1. 1 C4H10 contributes 10 H, balanced by 5 HCl gives:
   • 10 = y
   • So, y = 5
2. For Cl, since each Cl2 gives 2 Cl:
   • 2 = y + 1 → 2 = 5 + 1, which is incorrect. Thus, multiple HCl must be formed.

Step 5: Formulate Balanced Equation

• From balancing, we find:

2 C4H10 + 5 Cl2 → 2 C4H9Cl + 6 HCl

Final Balanced Equation:

• Thus, the balanced reaction is:

C4H10 + 4 Cl2 → 2 C4H9Cl + 2 HCl