What type of reaction is: CH4 + 2(O2) → CO2 + 2(H2O) + 218 kcal?
A. exothermic
B. combination
C. single replacement
D. endothermic
E. decomposition
The correct answer and explanation is:
Correct Answer: A. exothermic
This reaction is classified as an exothermic reaction. It represents the combustion of methane (CH₄) in the presence of oxygen (O₂) to produce carbon dioxide (CO₂), water (H₂O), and energy in the form of heat.
In an exothermic reaction, energy is released into the surroundings, often as heat or light. This release happens because the total energy required to break the bonds in the reactants is less than the energy released when new bonds form in the products. In this case, the equation shows a release of 218 kilocalories (kcal), indicating that energy is leaving the system.
The combustion of methane is a classic example of an exothermic process. Methane is a hydrocarbon, and when it burns in oxygen, it breaks down into carbon dioxide and water. During this process, a large amount of heat is generated. This heat is what powers many heating systems and cooking appliances that use natural gas.
The other choices can be ruled out based on the nature of the reaction:
- B. Combination reactions involve two or more substances combining to form one product. This is not the case here.
- C. Single replacement involves one element replacing another in a compound, which is not occurring.
- D. Endothermic is the opposite of exothermic and would involve absorption of heat, not its release.
- E. Decomposition reactions involve one compound breaking into simpler substances, which this reaction does not demonstrate.
Overall, the release of heat (218 kcal) confirms that this is an exothermic reaction.