Sure, let's answer each question in a detailed, step-by-step manner:
### 7.1 Is this reaction ENDOTHERMIC or EXOTHERMIC? Give a reason for the answer.
Answer: This reaction is EXOTHERMIC.
Reason: An exothermic reaction is one that releases energy to its surroundings, typically in the form of heat. Since the combustion of methane releases 891 kJ/mol of energy, this clearly indicates that the reaction is releasing energy. Hence, it is classified as exothermic.
### 7.2 Explain why all chemical reactions need activation energy.
Explanation:
Activation energy is the minimum energy required for a chemical reaction to occur. It is the energy needed to break the bonds in the reactants so that new bonds can form to create the products.
- Bond Breaking: Before new products can be formed, existing bonds in the reactants need to be broken. This requires an initial input of energy.
- Overcoming Barriers: Activation energy acts as a barrier to prevent spontaneous reactions. It ensures that molecules are at the right orientation and energy level to react successfully.
- Reaction Rate: The amount of activation energy affects the rate of the reaction. Higher activation energy means fewer molecules have the required energy to react, thus slowing down the reaction rate, while lower activation energy results in a faster reaction rate.
### 7.3 Why is this reaction not considered to be environmentally friendly?
Explanation:
Even though using methane as an alternative fuel might seem advantageous, the reaction is not environmentally friendly due to the following reason:
- Carbon Dioxide Emission: The combustion of methane leads to the production of carbon dioxide (CO₂). Carbon dioxide is a significant greenhouse gas, which contributes to global warming and climate change. The increased concentration of CO₂ in the atmosphere traps more heat, leading to a gradual increase in the Earth's temperature.
- Global Warming: The release of CO₂ exacerbates the greenhouse effect, causing detrimental environmental impacts such as rising sea levels, extreme weather patterns, and harm to wildlife.
Therefore, despite being an efficient fuel, the environmental cost of the CO₂ emissions makes this reaction environmentally unfriendly.
