MCAT Chemical and Physical Foundations of Biological Systems Flashcards: 5e Thermodynamics Energy Changes

What this deck covers

This deck focuses on 5e Thermodynamics Energy Changes, giving you a quick way to review the definitions, rules, and examples that matter most for MCAT Chemical and Physical Foundations of Biological Systems.

How to use these flashcards

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: Which sign of $\Delta H$ indicates an exothermic reaction at constant pressure?

Answer: $\Delta H<0$. Exothermic reactions release heat, corresponding to a decrease in the system's enthalpy.

Flashcard 2: What is the sign convention for $q$ when heat enters the system?

Answer: $q>0$. In thermodynamic conventions, heat absorbed by the system from surroundings is assigned a positive value.

Flashcard 3: What is the sign convention for $w$ when the system does work on the surroundings?

Answer: $w<0$. Work performed by the system on surroundings reduces the system's energy, thus assigned a negative sign.

Flashcard 4: State the first law of thermodynamics using $\Delta U$, $q$, and $w$.

Answer: $\Delta U=q+w$. The first law states that internal energy change equals heat added to the system plus work done on the system.

Flashcard 5: What is the formula for pressure–volume work at constant external pressure?

Answer: $w=-P_{\text{ext}}\Delta V$. For irreversible expansion at constant external pressure, work equals the negative product of pressure and volume change.

Flashcard 6: For an isochoric process, what is the work $w$?

Answer: $w=0$. Isochoric processes involve no volume change, hence no pressure-volume work is performed.

Flashcard 7: For an adiabatic process, what is the heat transfer $q$?

Answer: $q=0$. Adiabatic processes, by definition, prohibit heat exchange between the system and surroundings.

Flashcard 8: What is the relationship between $\Delta H$ and $q$ at constant pressure (PV work only)?

Answer: $\Delta H=q_p$. Enthalpy change equals heat transferred at constant pressure when only PV work occurs.

Flashcard 9: What is the relationship between $\Delta U$ and $q$ at constant volume?

Answer: $\Delta U=q_v$. At constant volume, internal energy change equals heat transferred since no work is done.

Flashcard 10: State the definition of enthalpy in terms of $U$, $P$, and $V$.

Answer: $H=U+PV$. Enthalpy accounts for internal energy plus the energy associated with pressure-volume work.

Flashcard 11: State the ideal gas law relating $P$, $V$, $n$, and $T$.

Answer: $PV=nRT$. The ideal gas law describes the proportional relationship between pressure, volume, moles, and temperature.

Flashcard 12: What is the formula for heat absorbed at constant pressure for a temperature change $\Delta T$?

Answer: $q_p=nC_p\Delta T$. Heat capacity at constant pressure quantifies energy required to raise temperature for a given amount of substance.

Flashcard 13: What is the formula for heat absorbed at constant volume for a temperature change $\Delta T$?

Answer: $q_v=nC_v\Delta T$. Heat capacity at constant volume measures energy input for temperature change without volume alteration.

Flashcard 14: State Hess's law for combining reaction enthalpies.

Answer: $\Delta H_{\text{net}}=\sum \Delta H_{\text{steps}}$. Since enthalpy is a state function, the net change equals the sum of stepwise changes regardless of path.

Flashcard 15: State the definition of entropy change for a reversible process.

Answer: $\Delta S=\frac{q_{\text{rev}}}{T}$. For reversible processes at constant temperature, entropy change is reversible heat divided by temperature.

Flashcard 16: What is the criterion for spontaneity in terms of the universe entropy change?

Answer: Spontaneous if $\Delta S_{\text{univ}}>0$. The second law dictates that spontaneous processes increase the total entropy of the universe.

Flashcard 17: State the Gibbs free energy equation relating $\Delta G$, $\Delta H$, $T$, and $\Delta S$.

Answer: $\Delta G=\Delta H-T\Delta S$. Gibbs free energy combines enthalpy and entropy to assess spontaneity at constant temperature and pressure.

Flashcard 18: At constant $T$ and $P$, what sign of $\Delta G$ indicates a spontaneous process?

Answer: $\Delta G<0$. Negative Gibbs free energy change indicates the process can occur spontaneously under those conditions.

Flashcard 19: What is the relationship between $\Delta G^\circ$ and the equilibrium constant $K$?

Answer: $\Delta G^\circ=-RT\ln K$. This equation links thermodynamic favorability under standard conditions to the equilibrium position.

Flashcard 20: Find $\Delta U$ if $q=-50\,\text{J}$ and $w=+20\,\text{J}$ for the system.

Answer: $\Delta U=-30\,\text{J}$. The first law calculates internal energy change as the sum of heat and work with proper signs.

Flashcard 21: Find $w$ if $P_{\text{ext}}=2\,\text{atm}$ and the system expands by $\Delta V=3\,\text{L}$.

Answer: $w=-6\,\text{L·atm}$. Expansion work against constant pressure is negative the product of pressure and volume increase.

Flashcard 22: Find $q_p$ if $n=2$ and $C_p=30\,\text{J·mol}^{-1}\text{·K}^{-1}$ for $\Delta T=10\,\text{K}$.

Answer: $q_p=600\,\text{J}$. Constant pressure heat transfer uses molar heat capacity to relate energy to temperature change.

Flashcard 23: Find $\Delta G$ at $T=300\,\text{K}$ if $\Delta H=20\,\text{kJ}$ and $\Delta S=50\,\text{J·K}^{-1}$.

Answer: $\Delta G=5\,\text{kJ}$. Gibbs free energy subtracts the entropy term from enthalpy, ensuring unit consistency in calculations.

Flashcard 24: What is the relationship between $C_p$ and $C_v$ for an ideal gas?

Answer: $C_p=C_v+R$. The difference arises from the additional work term at constant pressure for ideal gases.