Question

Please think about a reaction that is important to a system that you may have explored in a different class. These can be systems inside a cell, the ocean, the air, an engine, etc. Be creative and curious. Most important is how this information has helped you better understand the larger system. Instructions: 1. Describe the reaction or process. Where is it found? Why is it important? What is this reaction used for? 2. Enthalpy: What is the enthalpy change (in kJ/mol)? Describe the enthalpy changes taking place during this reaction. 3. Entropy: What is the entropy change (in J/mol)? Describe the entropy changes taking place during this reaction. 4. Is this reaction spontaneous? Calculate the change in free energy and/or the cell potential and describe the spontaneity of the reaction. If the reaction is spontaneous, how is that energy used? If the reaction is non-spontaneous, how does the reaction take place? Is it coupled to another reaction that overall makes both reactions spontaneous, such as ATP hydrolysis? 5. MOST IMPORTANT: How has learning about the thermodynamics of this reaction helped you better understand the larger system that this reaction is important to? 6. References: List all websites and resources that you used to help you understand this reaction and system better.​

Answer 1

I have explored many systems and reactions across various fields. One interesting reaction that I came across is photosynthesis, which is a fundamental process for all life on Earth. Photosynthesis takes place in the chloroplasts of plant cells, and it involves converting light energy into chemical energy in the form of glucose.

1. The overall reaction for photosynthesis can be written as:

6 C02 + 6 H2O + light energy-> C6H1206 +6 02

This reaction is crucial for the survival of plants and the organisms that depend on them. Plants use the glucose produced during photosynthesis as a source of energy to carry out various cellular processes. Additionally, the oxygen produced as a byproduct of

photosynthesis is essential for the respiration of organisms that depend on oxygen for survival.

2. The enthalpy change for photosynthesis is about +2800 kJ/mol, which means that the reaction requires energy input. Specifically, energy is absorbed from sunlight during the light-dependent reactions of photosynthesis.

3. The entropy change for photosynthesis is positive, indicating an increase in disorder or randomness. This increase in entropy is due to the conversion of light energy into chemical energy, which increases the number of available states for the system.

4. Photosynthesis is a non-spontaneous reaction, as it requires an energy input to proceed. The change in free energy for photosynthesis is positive, indicating that the reaction is not favorable under standard conditions. However, the reaction can be driven forward by coupling it with a spontaneous reaction, such as the hydrolysis of ATP.

5. Learning about the thermodynamics of photosynthesis has helped me understand the importance of energy transfer in biological systems. Photosynthesis is just one example of how organisms can convert one form of energy into another to meet their metabolic needs. Understanding the thermodynamics of these processes can help us design more efficient systems for producing energy or synthesizing chemicals.

6. Sources:

• Campbell Biology, 11th edition

• Khan Academy: Photosynthesis