Glycolysis is the process by which glucose is metabolized to...

Glycolysis is the process by which glucose is metabolized to lactic acid according to the equation $$ \begin{array}{c} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q) \longrightarrow 2 \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}(a q) \\ \Delta G^{\circ}=-198 \mathrm{~kJ} \text { at } \mathrm{pH} 7.0 \text { and } 25^{\circ} \mathrm{C} \end{array} $$ Glycolysis is the source of energy in human red blood cells. In these cells, the concentration of glucose is $5.0 \times 10^{-3} \mathrm{M},$ while that of lactic acid is $2.9 \times 10^{-3} \mathrm{M}$. Calculate $\Delta G$ for glycolysis in human blood cells under these conditions. Use the equation $\Delta G=\Delta G^{\circ}+\mathrm{RT} \ln Q,$ where $Q$ is the concentration quotient, analogous to $K$.

Glycolysis is the process by which glucose is metabolized to lactic acid according to the equation
$$
\begin{array}{c}
\mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}(a q) \longrightarrow 2 \mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}_{3}(a q) \\
\Delta G^{\circ}=-198 \mathrm{~kJ} \text { at } \mathrm{pH} 7.0 \text { and } 25^{\circ} \mathrm{C}
\end{array}
$$
Glycolysis is the source of energy in human red blood cells. In these cells, the concentration of glucose is $5.0 \times 10^{-3} \mathrm{M},$ while that of lactic acid is $2.9 \times 10^{-3} \mathrm{M}$. Calculate $\Delta G$ for glycolysis in human blood cells under these conditions. Use the equation $\Delta G=\Delta G^{\circ}+\mathrm{RT} \ln Q,$ where $Q$ is the concentration quotient, analogous to $K$.

Key Concepts

Gibbs Free Energy

Gibbs free energy (?G) quantifies the amount of energy available to do work during a chemical reaction at constant temperature and pressure. It indicates reaction spontaneity, with negative values signifying that a process can occur spontaneously, and is fundamental in understanding how reactions proceed in both chemical and biological systems.

Standard Gibbs Free Energy Change

The standard Gibbs free energy change (?G°) is measured under standard conditions (e.g., 1 M concentrations for solutes, 1 atm pressure for gases, and a specified temperature, typically 25°C). It provides a baseline energy difference for a reaction, allowing comparison between different reactions or the adjustment for non-standard conditions using thermodynamic equations.

Reaction Quotient

The reaction quotient (Q) is the ratio of the concentrations (or activities) of the products to those of the reactants, each raised to their stoichiometric coefficients, at any point during the reaction. Q is used in the equation ?G = ?G° + RT ln Q to adjust the free energy change for conditions that deviate from standard state, helping to predict the direction in which the reaction will proceed.

Role of Temperature and the Gas Constant

Temperature (T) and the gas constant (R) are crucial parameters in the thermodynamic equation relating ?G°, Q, and ?G. The term RT ln Q accounts for how temperature affects the impact of concentration differences on the free energy change, thus integrating thermal effects into the spontaneity and equilibrium of chemical reactions.

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