I got the calculation. I\'m just confused by the last bit asking if it\'s exothe

Question

I got the calculation. I'm just confused by the last bit asking if it's exothermic or endothermic. Isn't that impossible to determine in this case without being given the change in enthalpy or entropy?

ful Information: R 8.314 JK mol Henderson-Hasselbalch Equation: pHpK + log IA] [HA] Calculate the AG, for the isomerization of dihydroxyacetone phosphate (DHAP) to glyceraldehydes 3- phosphate (GAP). This reaction takes place in glycolysis. At equilibrium, the ratio of GAP to DHAP is 0.0-75 at 25 'C and pHi7 ts the raetion exotheminsy

Explanation / Answer

Yes, your are right. You cant find out if the reaction is exothermic or endothermic without being given the change in enthalpy or entropy. But generally isomerization of DHAP to GAP are exergonic with means there is a positive flow of energy from system to surroundings.

This reaction takes place in glycolysis. At equilibrium, the ratio of GAP to DHAP is 0.0475 at 25°C (298 K) and pH 7. Hence, Keq = 0.0475. The standard free-energy change for this reaction is then calculated from equation 5:

G°=-RTln(Keq)
=-8.315 × 10^-3(298)(ln(0.0475))
=7.53 kJ/mol

Under these conditions, the reaction is endergonic. DHAP will not spontaneously convert into GAP.
Substituting these values into equation 1 gives

G=7.53 kJ/mol+RTln((3 × 10^6)/(2 × 10^4))=-2.89 kJ/mol

This negative value for G indicates that the isomerization of DHAP to GAP is exergonic and can take place spontaneously when these species are present at the preceding concentrations. Note that G for this reaction is negative, although G° is positive.

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