CH bonds are flammable primarily because the electrons within them possess high energy, which is released intensely during combustion.
The flammability of substances containing carbon-hydrogen (C-H) bonds, such as hydrocarbons (like methane, propane, and gasoline), stems from the chemical energy stored within these bonds. When these substances react rapidly with oxygen, a process known as combustion, this stored energy is released as heat and light.
Based on the provided information, a key reason for this flammability is that:
- High-Energy Electrons: The electrons associated with CH and CC bonds are high energy compared to the electrons and the OH bond and the CO bonds of the products.
During combustion, the C-H bonds (and C-C bonds in hydrocarbons) are broken, and new, more stable bonds are formed, typically carbon-oxygen (C=O) in carbon dioxide and hydrogen-oxygen (O-H) in water.
Here's a breakdown of why this energy difference matters:
- Energy Storage: The electrons in the CH and CC bonds are in a relatively high-energy state. Think of it like holding a ball high in the air – it has potential energy.
- Energy Release: When these high-energy bonds break and lower-energy bonds (like C=O and O-H) form in the products (CO₂ and H₂O), the system moves to a lower energy state. The excess energy is released into the surroundings.
- Combustion Reaction: The overall reaction looks simplified like this:
Hydrocarbon (with C-H/C-C bonds) + Oxygen → Carbon Dioxide (with C=O bonds) + Water (with O-H bonds) + Energy (Heat and Light)
Substances like alcohols are also flammable because they still contain significant amounts of these high-energy C-H bonds, which can readily combine with oxygen and release energy.
Understanding the energy difference between the reactant bonds (C-H, C-C) and the product bonds (C=O, O-H) is fundamental to explaining why hydrocarbons and other organic compounds containing CH bonds are effective fuels and exhibit flammability. It's the transition from a higher-energy molecular arrangement to a lower-energy one that drives the exothermic process of combustion.
