thermodynamics 2 Flashcards
(30 cards)
Q: Give two examples of energy transformation.
A: Potential to kinetic (falling ball), and kinetic to potential (rising lift).
Q: How can a closed system exchange energy with its surroundings?
A: Through heat or work.
Q: What kind of work do most chemical reactions perform?
A: Most chemical reactions only perform pV (pressure-volume) work, which is usually negligible due to small volume changes.
Q: What is enthalpy (H)?
A: Enthalpy is the total energy of a system, defined as H = U + pV, where U is internal energy.
Q: What is the equation for enthalpy (H)?
A: H = U + pV
Q: What happens to ΔH when a system does no pV work but absorbs 10 kJ of heat?
A: ΔU = +10 kJ and ΔH = ΔU = +10 kJ, so enthalpy increases by 10 kJ.
Q: Why are enthalpy changes (ΔH) more useful than absolute values?
A: Because changes in enthalpy indicate heat flow, which relates directly to energy changes in a reaction.
Q: What does a positive ΔH signify?
A: The system absorbs heat (endothermic process).
Q: What does a negative ΔH signify?
A: The system releases heat (exothermic process).
Q: Does the sign of ΔH alone determine the favorability of a reaction?
A: No, enthalpy alone is not sufficient to determine favorability.
Q: What additional concept is needed to understand reaction favorability?
A: Entropy (S), which measures the disorder or number of ways a system can be arranged.
Q: What happens to entropy when gas molecules spread out in a closed system?
A: Entropy increases due to increased disorder.
Q: What is the relationship between entropy and the number of arrangements of a system?
A: Entropy is proportional to the number of ways the system can be arranged (W).
Q: Is the entropy change (ΔS) positive when a system becomes more disordered?
A: Yes, ΔS is positive when disorder increases.
Q: What is the total entropy change equation?
A: ΔS_total = ΔS_system + ΔS_surroundings
Q: What is Boltzmann’s interpretation of entropy?
A: Entropy is related to the number of microstates (W): S ∝ ln(W)
Q: What is the formula relating entropy change to heat and temperature?
A: ΔS = ΔQ / T
Q: In the ice cube example, why does heat flow from the room to the ice?
A: Due to a temperature difference between the surroundings (273.1 K) and the system (273 K).
Q: What is the entropy change in the system when heat flows into ice at 273 K?
A: ΔS_system = |ΔQ| / 273 K
Q: What is the entropy change in the surroundings during the ice cube example?
A: ΔS_surroundings = |ΔQ| / 273.1 K
Q: Why is the total entropy change positive in the melting ice cube example?
A: Because ΔS_system > ΔS_surroundings, meaning the overall ΔS_total is positive.
Q: What happens when there is no temperature gradient between system and surroundings?
.
A: No further heat flow occurs
Q: What is the condition for a process to be thermodynamically favorable?
A: ΔS_total > 0
Q: How is entropy best visualized?
A: As a measure of the level of disorder in a system
