For a particular chemical reaction, the enthalpy of the reactants is -400 kJ. The enthalpy of the products is -390 kJ. The entropy of the reactants is 0.2 kJ/K. The entropy of the products is 0.3 kJ/K. The temperature of the reaction is 25 degrees Celsius. What can you conclude about this reaction?
A. It is exergonic
B. It is endergonic
C. it is a redox reaction
D. It is being catalyzed by an enzyme
Clarify Question
What is the key concept addressed by the question?
What type of thinking is required?
Gather Content
What do you already know aboutenergy of reactants and products in a reaction? What other information is related to the question?
Choose Answer
Do you have all the information needed to make a determination about the change in free energy?
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
A. It is exergonic
Clarify Question
What is the key concept addressed by the question?
· The question asks you to draw a conclusion about a reaction given different energy parameters of reactants and products.
What type of thinking is required?
· You are being asked to dissect, or analyze, several energy parameters of a reaction in order to arrive at a conclusion.
Gather Content
What do you already know aboutenergy of reactants and products in a reaction? What other information is related to the question?
· Remember that the total energy (enthalpy or H) in a chemical system is equal to the amount of free energy (G) minus the amount of disorder (entropy) at a particular temperature (T, in Kelvin). Thus, H = G – TS.
· Recall also that delta G equals the difference in energy level from the beginning to the end of the reaction, such that delta G = delta H – T(delta S). Consider also that reactions that have a negative delta G are considered to be exergonic (spontaneous), whereas positive delta G reactions are endergonic (nonspontaneous).
· How is the overall delta G of a reaction determine once you have values for total energy (enthalpy) and wasted energy (entropy)?
Choose Answer
Do you have all the information needed to make a determination about the change in free energy?
· Recall that delta G refers to the amount of energy that changes from the beginning to the end of the reaction, and is equal to the total change in enthalpy (delta H) minus the product of temperature (T, in Kelvin) and disorder (S).
· Let’s unpack this solution by first comparing the total energy between products and reactants. If you compare the enthalpy (total energy) of the products and reactants, you will find the change in enthalpy is -390kJ –(-400kJ), which equals 10kJ.
· Next let’s determine the disorder component, which is the product of entropy and temperature in Kelvin. Change in entropy is 0.3kJ/K – 0.2kJ/K and equals 0.1 kJ/K. The temperature in Kelvin is 25 degrees Celsius + 273K and equals 298K.
· Finally, the change in free energy is determined by change in enthalpy minus the disorder component. Thus, delta G = (10-(298*0.1)), which equals (10-29.8), which produces a final answer of -19.8. Since the change in free energy is negative for this reaction, it is exergonic. Note that it cannot be concluded from the description whether this is a redox reaction, or whether it is being catalyzed by an enzyme.
Reflect on Process
Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
· This question asked you to analyze energy characteristics for a reaction to determine whether it is exergonic, endergonic, redox, or enzyme-catalyzed.
· If you got the answer correct, well done! This was a more challenging problem to solve.If you got an incorrect answer, did you recall how delta G is different between exergonic and endergonic reactions? Were you able to calculate the change in free energy based on the information provided? Based on that information, were you able to show the reaction had a negative delta Gand based on that must be exergonic?
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