Final answer:
The correct answer is option 4) Exothermic reaction. The graph of an exothermic reaction represents a type of reaction where energy is released, typically as heat, as the products have a lower energy level than the reactants. The correct answer is 4) Exothermic reaction.
Step-by-step explanation:
The graph of an exothermic reaction represents a type of reaction where energy is released into the environment. This is observed when the products of a chemical reaction have a lower energy level than the reactants. Specifically, the energy stored in the chemical bonds of the reactants is higher than that of the products, and this excess energy is released, typically in the form of heat. Therefore, the correct answer to the question 'What type of reaction is represented by the graph of an exothermic reaction?' is 4) Exothermic reaction.
An example of an exothermic reaction is the combustion of methane, where heat is released:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(l) with the release of energy. In an exothermic reaction, heat is released from the system and transferred to the surroundings. This results in a decrease in the potential energy of the reactants, with the products having lower energy than the reactants. Exothermic reactions often occur spontaneously and are commonly illustrated using reaction coordinate diagrams that show the products as being lower in energy than the reactants.