Why is why is CH4+2O2 --> CO2+2H2O very slow at room temperature?

The activation energy is high.

The chemical reaction you mentioned, CH4 + 2O2 -> CO2 + 2H2O, is the combustion reaction of methane, which is a hydrocarbon found in natural gas. In general, combustion reactions are exothermic (they release heat) and can occur at room temperature if an initial spark or high enough temperature is provided to overcome the activation energy, which is the minimum energy required for the reaction to start.

However, at room temperature (around 25 degrees Celsius or 77 degrees Fahrenheit), the reaction between methane and oxygen is relatively slow because the activation energy is not readily provided. Therefore, the reaction does not proceed spontaneously without an external source of energy, such as a spark or a high-temperature flame.

To explain why the reaction is slow at room temperature, we need to consider the energy barrier called activation energy. Activation energy is the minimum amount of energy required for the reactant molecules to collide with enough force to break the existing bonds and form new ones, resulting in the product molecules.

In the case of the combustion of methane, the activation energy is quite high. At room temperature, the kinetic energy of the methane and oxygen molecules is not sufficient to overcome this energy barrier consistently, resulting in a relatively slow reaction rate.

To make the reaction proceed at a faster rate at room temperature, you would need to introduce a catalyst. A catalyst is a substance that can lower the activation energy required for a reaction, thereby increasing the reaction rate without being consumed itself. In the case of methane combustion, a common catalyst is platinum, which helps to facilitate the reaction and make it occur more readily at lower temperatures.

In summary, the combustion reaction of methane (CH4 + 2O2 -> CO2 + 2H2O) is slow at room temperature because the activation energy for the reaction is high and not readily provided by the surrounding conditions. To increase the reaction rate, a catalyst such as platinum can be used to lower the activation energy requirement.