Imagine a graph. The x-axis is labeled “time” and is measured in seconds, and the y axis is labeled “potential energy” and is measured in kilojoules. The slope starts at 0 seconds with a plateau at 25 kj. This plateau is labeled as “reactants”. The slope then rises to a peak labeled “activation energy” at 78 kj. Finally the slope drops to a plateau at 14 kj and is labeled “products”.
What does the graph described above represent?
A. Rate of reaction graph
B. An endothermic reaction
C. A phase change graph
D. An exothermic reaction
d because the products are lower energy than the reactants.
D
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E. A rollercoaster ride for molecules
D. An exothermic reaction
The graph described above represents a potential energy diagram for a chemical reaction.
To understand and answer the question, we can analyze the information provided in the description of the graph. Here are the key points:
1. The x-axis represents time, measured in seconds.
2. The y-axis represents potential energy, measured in kilojoules.
3. The graph has three main sections:
a. A plateau at 25 kJ, labeled as "reactants."
b. A rise to a peak at 78 kJ, labeled as "activation energy."
c. A drop to a plateau at 14 kJ, labeled as "products."
Based on this information, we can determine the answer to the question:
- Option A: Rate of reaction graph: The graph does not give any information about the rate of reaction. So, it is not an appropriate answer.
- Option B: An endothermic reaction: An endothermic reaction is characterized by absorbing heat or energy from the surroundings, resulting in an increase in potential energy. The graph shows a rise in potential energy from the reactants to the activation energy, suggesting an input of energy. Therefore, this option may be a possible answer.
- Option C: A phase change graph: A phase change graph typically represents the change in energy required to change the state of matter (e.g., solid to liquid). The graph provided does not indicate any phase change, so this option is not applicable.
- Option D: An exothermic reaction: An exothermic reaction releases heat or energy to the surroundings, resulting in a decrease in potential energy. The graph shows a drop in potential energy from the activation energy to the products, suggesting an output of energy. Therefore, this option may also be a possible answer.
To determine the correct answer between B (endothermic reaction) and D (exothermic reaction), we need to consider the overall trend of the graph. Since the potential energy decreases from the activation energy to the products, indicating an overall release of energy, the correct answer is:
D. An exothermic reaction.