Which of the following compounds would you predict to be highest in energy?

• A. C_2H_2 (acetylene)
• B. CH_4 (methane)
• C. C_2H_4 (ethylene)
• D. C_2H_6 (ethane)

Answer: (A)

Verified step by step guidance

1. Step 1: Understand that the energy of a compound is related to the stability of its chemical bonds. Generally, molecules with more strained or higher-energy bonds are less stable and thus higher in energy.
2. Step 2: Identify the types of bonds present in each compound: CH_4 (methane) has only single C–H and C–C bonds; C_2H_6 (ethane) has a single C–C bond and C–H bonds; C_2H_4 (ethylene) has a double C=C bond; C_2H_2 (acetylene) has a triple C≡C bond.
3. Step 3: Recall that multiple bonds (double and triple bonds) contain more energy than single bonds because they involve pi bonds in addition to sigma bonds, which are generally higher in energy and less stable than single bonds.
4. Step 4: Compare the bond energies and stabilities: triple bonds (acetylene) are higher in energy than double bonds (ethylene), which are higher than single bonds (ethane and methane). Also, methane is a single carbon compound, so it generally has lower energy compared to compounds with multiple carbons and multiple bonds.
5. Step 5: Conclude that among the given compounds, acetylene (C_2H_2) with its triple bond is predicted to be highest in energy due to the presence of the high-energy triple bond.