Question

Carbon cannot react with oxygen in air at ordinary temperature because (1) carbon has no reaction with oxygen (2) the activation cnergy of the reaction of carbon with oxygen is very high (3) carbon becomes passive in air (4) carbon and oxygen both arc nonmctals

Short answer

Option (2): the activation energy is very high.

Step-by-step solution

Understand the options

Read the given options carefully. The question is asking why carbon does not react with oxygen in the air at ordinary temperature.

Eliminate incorrect options

Option (1) suggests carbon has no reaction with oxygen, which is incorrect because carbon can react with oxygen at higher temperatures. Option (3) suggests carbon becomes passive, which is not accurate. Option (4) simply states their non-metallic nature, which doesn't explain the lack of reaction at ordinary temperature.

Analyze the correct option

Option (2) states that the activation energy is very high. Understanding activation energy: it is the minimum amount of energy required for a reaction to occur. A high activation energy means the reactants need more energy to initiate the reaction.

Conclusion

Since carbon requires significant energy to overcome the activation energy barrier and react with oxygen, such a reaction does not happen at ordinary temperatures.

Key concepts

carbon and oxygen reaction

Carbon and oxygen can indeed react, but not under normal conditions. When carbon (like in charcoal) burns in the presence of oxygen, it forms carbon dioxide (CO₂), releasing energy. This is a well-known combustion reaction.
However, at room temperature, this reaction does not happen. This is because the molecules of carbon and oxygen need sufficient energy to start reacting. This required energy is called activation energy. Without enough activation energy, carbon and oxygen molecules simply stay as they are, not reacting with each other in daily life.

activation energy barrier

The activation energy barrier is a crucial concept in understanding why some reactions do not occur spontaneously at normal temperatures.
It denotes the minimum energy required for reactants to transform into products. In simpler terms, it’s like the push needed to get a car moving from a standstill. Without this push, the car won't move; similarly, without sufficient activation energy, a chemical reaction won't start.
In the case of carbon and oxygen, the activation energy barrier is quite high. This means that at ordinary temperatures, there isn’t enough energy to overcome this barrier and start the reaction. That’s why carbon doesn't burn in oxygen under normal conditions, even though it can at higher temperatures.

reaction temperature

Temperature plays a significant role in chemical reactions. Increasing the temperature usually provides the molecules with more energy. This can help them overcome the activation energy barrier.
For the reaction between carbon and oxygen, when we apply heat (like when lighting a fire), we provide the necessary energy for the molecules to start reacting. Once they have enough energy, the reaction continues, releasing heat and forming carbon dioxide.
So, while carbon doesn't react with oxygen at room temperature, increasing the temperature can initiate the reaction. This is why we need to ignite the charcoal in a barbecue to get it burning.