Which of the following is an example of an exothermic reaction?
A.
Melting ice
B.
Burning wood
C.
Cooking an egg
D.
Dissolving sugar in water
The Correct answer and Explanation is:
The correct answer is B. Burning wood.
Explanation:
Exothermic reactions are chemical reactions that release energy, usually in the form of heat, into the surrounding environment. In an exothermic reaction, the energy of the products is lower than the energy of the reactants, and the difference in energy is released during the reaction.
- Burning Wood (B): Burning wood is a classic example of an exothermic reaction. When wood burns, it undergoes combustion, a chemical reaction with oxygen that produces carbon dioxide, water, and heat. The overall reaction can be represented as: C6H12O6+6O2→6CO2+6H2O+Heat\text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O} + \text{Heat}C6H12O6+6O2→6CO2+6H2O+Heat Here, the chemical bonds in the wood (composed primarily of cellulose) are broken and rearranged, releasing energy in the form of heat and light. This is why burning wood warms up the surroundings and produces visible flames.
- Melting Ice (A): Melting ice is an endothermic process, not exothermic. To melt ice, heat energy must be absorbed from the surroundings to break the hydrogen bonds between water molecules in the solid phase, converting ice to liquid water. This absorption of heat results in a cooling effect.
- Cooking an Egg (C): Cooking an egg is another example of an endothermic process. When an egg is cooked, heat is absorbed to denature the proteins in the egg white and yolk, changing their structure and causing the egg to solidify. The heat is absorbed from the cooking source, and energy is taken in from the surroundings.
- Dissolving Sugar in Water (D): Dissolving sugar in water is typically a process that can be either endothermic or exothermic, but in most cases, it is endothermic. The process requires energy to break the intermolecular forces between sugar molecules and to interact with the water molecules. As a result, the solution usually absorbs heat from the surroundings.
In summary, burning wood is an exothermic reaction because it releases energy in the form of heat and light, while the other options involve processes that either absorb heat or are not clearly exothermic.