Hello,
I'm confused on what these problems are telling me. Is questions a) and b) the same? I don't know, please help me I don't know what to do...
The inteconversion of DHAP and G3P is a part of both the glycotic pathway and the Calvin cycle for phoyosynthetic carbon fixation.
DHAP----->G3P
The valeu of deltaG0 for this reaction is +1.8 kcal/mol at 25 degrees celsius. In the glycotic pathway, this reaction goes to the right, converting DHAP to G3P. In the calvin cycle, this reaction proceeds to the left converting G3P to DHAP.
a)which direction does the equlibirum lie? What is the equilibirum constant at 25 degrees celsius?
b)In which direction does this rxn tend to proceed under standard conditions? What is deltaG for the reaction in that direction?
c)In the glycotic pathway, this reaction is driven to the right because G3P is consumed by the next reaction in sequence, thereby maintaining a low G3P concentration. What will delta G be (at 25 degrees celcius) if the concentration of G3P is maintained at 1% of the DHAP concentration?
d)In the calvin cycle, this rxn proceeds to the left. How high must the (g3p)/(dhap) ratio be to ensure that the reaction is exergonic by at least -3.0 kcal/mot (at 25 degrees celsius)?
You are right Krissy...questions a and b sound the same..."in which directin does the equilibrium lie" and "in which direction does the rxn proceed..." to me mean the same. In this example, since Gibbs free energy is >0, then the reaction spontaneoulsy goes the other way, or backward, or right to left.
Part a also asks for the equilibrium constant, K. Did you learn the relationship between the G and the equilib constant? It is given by the equation: deltaG = -RT lnK, or deltaG = -2.303RTlogK.
Part b...yes, it goes right to left, and the delta G for the spontaneous reaction is -1.8.
part c: here you are given the concentrations, so your equilbirium constant changes, thus driving the delta G the other way...
part d: this seems hard to me. I guess I would first calculate the delta S of the reaction: delta S = (deltaH - deltaG)/T.
Then once you know the delta S, ther is a relationship between the equilibe constant and delta H and delta S:
logK = (-deltaH/2.303RT) + (deltaS/2.303R).
Sorry if there's an easier way that I'm not seeing!
still kinda confused..sorry.
No problem! Understanding thermodynamics can be complex. Let's break down the questions and their solutions step by step:
a) In this question, we're asked about the direction in which the equilibrium lies. Since the value of ΔG0 is positive (+1.8 kcal/mol), it means that the reaction is not favorable in the forward direction (from DHAP to G3P). Therefore, the equilibrium lies towards the left, or in other words, the reaction tends to proceed in the reverse direction.
To find the equilibrium constant (K) at 25 degrees Celsius, we can use the equation ΔG = -RT ln K, where R is the gas constant and T is the temperature. This equation relates the ΔG and the equilibrium constant.
b) For this question, we need to determine the direction in which the reaction tends to proceed under standard conditions. Since the ΔG value is +1.8 kcal/mol, it indicates that the forward reaction (DHAP to G3P) is not spontaneous. Instead, the reaction tends to proceed in the reverse direction (G3P to DHAP) under standard conditions.
c) In the glycolytic pathway, the reaction proceeds to the right because G3P is consumed by the next reaction, which maintains a low G3P concentration. To calculate the ΔG when the concentration of G3P is maintained at 1% of the DHAP concentration, we can use the equation ΔG = ΔG0 + RT ln(Q), where Q is the reaction quotient. Q is calculated based on the concentrations of reactants and products. With the given condition, you can substitute the concentrations into the equation to find the ΔG value.
d) In the Calvin cycle, the reaction proceeds to the left (G3P to DHAP). To determine the required (G3P)/(DHAP) ratio to ensure the reaction is exergonic by at least -3.0 kcal/mol, we can use the equation that relates the equilibrium constant (K) to ΔH and ΔS: logK = (-ΔH/2.303RT) + (ΔS/2.303R). Rearranging this equation, you can solve for the (G3P)/(DHAP) ratio.
I hope this explanation clarifies the questions for you. If you have any further questions, feel free to ask!