MCAT Biological and Biochemical Foundations of Living Systems Flashcards: 1d Bioenergetics Thermodynamics

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This deck focuses on 1d Bioenergetics Thermodynamics, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Biological and Biochemical Foundations of Living Systems.

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Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

Flashcard 1: Identify the sign of $\Delta G$ for a reaction with $\Delta H > 0$ and $\Delta S < 0$ at any $T$.

Answer: $\Delta G > 0$ at all $T$. Positive enthalpy and negative entropy ensure the Gibbs free energy remains positive, preventing spontaneity at any temperature.

Flashcard 2: Identify when $\Delta G$ is negative if $\Delta H > 0$ and $\Delta S > 0$.

Answer: Negative at high $T$. At high temperatures, the large negative $-T\Delta S$ term overcomes the positive enthalpy, making free energy negative.

Flashcard 3: What sign of $\Delta S$ indicates an increase in entropy (greater dispersal of energy/microstates)?

Answer: $\Delta S > 0$. Positive entropy change signifies increased molecular disorder or more accessible microstates, aligning with the second law of thermodynamics.

Flashcard 4: What is the definition of an endergonic reaction in terms of $\Delta G$?

Answer: $\Delta G > 0$. Endergonic processes require free energy input from surroundings to proceed, characterized by a positive change in Gibbs free energy.

Flashcard 5: What condition on $\Delta G$ indicates a process is at equilibrium (no net change) at constant $T$ and $P$?

Answer: $\Delta G = 0$. At equilibrium, the system's free energy is minimized, resulting in no net driving force for forward or reverse processes.

Flashcard 6: What is the sign of $\Delta G^\circ$ when $K < 1$?

Answer: $\Delta G^\circ > 0$. An equilibrium constant less than one signifies reactant-favored reactions, resulting in positive standard free energy change.

Flashcard 7: Identify the sign of $\Delta G$ for a reaction with $\Delta H < 0$ and $\Delta S > 0$ at any $T$.

Answer: $\Delta G < 0$ at all $T$. With negative enthalpy and positive entropy, both terms in the Gibbs equation contribute to spontaneity regardless of temperature.

Flashcard 8: What is the MCAT-appropriate definition of enthalpy change, $\Delta H$?

Answer: Heat transferred at constant pressure. Enthalpy change measures heat exchange during reactions or phase changes when pressure remains constant, as per thermodynamic definitions.

Flashcard 9: What is the definition of an exergonic reaction in terms of $\Delta G$?

Answer: $\Delta G < 0$. Exergonic processes release free energy to surroundings, driven by a negative change in Gibbs free energy under constant conditions.

Flashcard 10: What condition on $\Delta G$ indicates a process is thermodynamically spontaneous at constant $T$ and $P$?

Answer: $\Delta G < 0$. Negative free energy change drives processes toward lower energy states, enabling spontaneity without external input under constant conditions.

Flashcard 11: What is the formula linking standard free energy and equilibrium constant?

Answer: $\Delta G^\circ = -RT\ln K$. This relation connects thermodynamic favorability under standard conditions to the equilibrium constant via temperature and the gas constant.

Flashcard 12: Which inequality between $Q$ and $K$ makes $\Delta G$ negative (net forward reaction favored)?

Answer: $Q < K$. When the reaction quotient is below the equilibrium constant, the system shifts forward to minimize free energy.

Flashcard 13: What is the sign of $\Delta G^\circ$ when $K > 1$?

Answer: $\Delta G^\circ < 0$. An equilibrium constant greater than one indicates product-favored reactions, corresponding to negative standard free energy change.

Flashcard 14: What effect does a catalyst (enzyme) have on $\Delta G$ and on $E_a$?

Answer: $\Delta G$ unchanged; $E_a$ decreased. Catalysts lower the activation energy by stabilizing the transition state, but thermodynamics dictate that free energy difference remains constant.

Flashcard 15: What effect does a catalyst (enzyme) have on the equilibrium constant $K$?

Answer: $K$ unchanged. Catalysts equally accelerate forward and reverse rates, maintaining the ratio that defines the equilibrium constant unchanged.

Flashcard 16: What is the relationship between spontaneity and rate (kinetics) for a reaction on the MCAT?

Answer: Spontaneous does not imply fast. Thermodynamic spontaneity assesses feasibility based on energy changes, independent of kinetic factors that determine reaction speed.

Flashcard 17: Identify when $\Delta G$ is negative if $\Delta H < 0$ and $\Delta S < 0$.

Answer: Negative at low $T$. At low temperatures, the negative enthalpy term dominates over the smaller positive $-T\Delta S$ contribution in the Gibbs equation.

Flashcard 18: What is the definition of activation energy, $E_a$, in reaction kinetics?

Answer: Energy barrier to reach the transition state. Activation energy quantifies the kinetic barrier reactants must overcome to form the high-energy transition state in a reaction pathway.

Flashcard 19: What is the definition of Gibbs free energy change, $\Delta G$, for a process at constant $T$ and $P$?

Answer: $\Delta G = \Delta H - T\Delta S$. This equation quantifies the free energy available for work by balancing enthalpy and entropy contributions at constant temperature and pressure.

Flashcard 20: What is the formula for nonstandard free energy change in terms of reaction quotient $Q$?

Answer: $\Delta G = \Delta G^\circ + RT\ln Q$. This equation adjusts standard free energy for non-equilibrium conditions by incorporating the reaction quotient and thermal energy.

Flashcard 21: What is the relationship between $\Delta G$ and maximum nonexpansion work, $w_{\max}$, at constant $T$ and $P$?

Answer: $\Delta G = -w_{\max}$. Gibbs free energy change represents the maximum reversible work extractable, excluding pressure-volume work, under isothermal-isobaric conditions.

Flashcard 22: Which inequality between $Q$ and $K$ makes $\Delta G$ positive (net reverse reaction favored)?

Answer: $Q > K$. When the reaction quotient exceeds the equilibrium constant, the system favors the reverse direction to reach equilibrium.

Flashcard 23: Find $\Delta G$ given $\Delta H = 10\ \text{kJ/mol}$, $\Delta S = 20\ \text{J/(mol\cdot K)}$, $T = 300\ \text{K}$.

Answer: $\Delta G = 4\ \text{kJ/mol}$. Convert $\Delta S$ to kJ/mol·K, compute $T\Delta S = 6$ kJ/mol, then subtract from $\Delta H$ using the Gibbs free energy equation.

Flashcard 24: What sign of $\Delta H$ corresponds to an exothermic reaction?

Answer: $\Delta H < 0$. Exothermic processes release heat to surroundings, reducing the system's internal energy and thus yielding a negative enthalpy change.