Week 25 / Thermodynamics 1 Flashcards
Q: What is the formula for Free Energy (G)?
G=H−TS
G = Gibbs Free Energy,
H = Enthalpy Change,
T = Temperature (Kelvin),
S = Entropy change
Q: What is the formula for the change in Free Energy ?
ΔG=ΔH−TΔS
ΔG = Gibbs Free Energy,
ΔH = Enthalpy Change,
T = Temperature (Kelvin),
ΔS = Entropy change
Q: What is the formula for the change in activation Free Energy
ΔG ‡=ΔH ‡−TΔS ‡
Q: What does a negative
Δ𝐻 (−Δ𝐻) indicate in a chemical reaction?
It indicates the formation of new, stronger, or more stable covalent bonds or favorable solvent interactions (non-covalent).
Q: At what temperature does entropy (𝑇Δ𝑆) have a higher contribution to free energy?
A: At higher temperatures.
Q: At what temperature does enthalpy (Δ𝐻) have a larger contribution to free energy?
A: At low temperatures.
Q: What do changes in enthalpy (Δ𝐻) deal with?
A: Changes in chemical bonding or non-covalent interactions.
Q: What do changes in entropy (Δ𝑆) deal with?
A: Changes in order or disorder associated with the process of interest.
Q: What are the two main types of energy?
A: Kinetic energy and potential energy.
Q: What is kinetic energy?
A: Energy associated with movement.
Q: What is the formula for classical kinetic energy (𝐸𝐾)?
A:
𝐸 𝐾= 1/2 mass ⋅ velocity^2
Q: What is potential energy?
A: Energy possessed due to position.
Q: What is the formula for potential energy (𝐸𝑃)
E P =mass⋅gravity⋅height
Q: What does the law of conservation of energy state?
A: Energy can neither be created nor destroyed.
What is the formula for total energy
(𝐸)?
E=Ek+Ep
Q: How is energy transferred?
A: Energy is transferred from one place to another in varying forms.
Q: What happens to energy when it is dissipated?
A: It becomes heat energy, which is non-useable and associated with high entropy.
Q: What is a system in thermodynamics?
A: The system is the vessel of interest, such as reaction flasks, biological cells, or whole animals.
Q: What are surroundings in thermodynamics?
A: The surroundings are the place where observations are recorded, typically assumed to have constant volume or pressure.
Q: How do the surroundings behave relative to changes in the system?
A: The surroundings remain constant regardless of changes to the system.
Q: Give examples of what can be considered a system.
A: Reaction flasks, biological cells, or whole animals.
Q: What is an open system?
Q: What is a closed system?
Q: What is an isolated system?
A: A system that can exchange both energy and matter with its surroundings.
A: A system that can exchange energy but not matter with its surroundings.
A: A system that exchanges neither energy nor matter with its surroundings.
Q: What are diathermic barriers?
A: Barriers, such as metals, skin, and biological membranes, that allow efficient energy transfer.
Q: What is heating in thermodynamics?
A: Heating is the energy transfer between a system and its surroundings.
Q: What are adiabatic barriers?
A: Barriers that prevent the transfer of energy, even when significant temperature differences exist.
Q: Which type of barrier allows energy transfer efficiently?
Q: Which type of barrier prevents energy transfer completely?
A: Diathermic barriers.
A: Adiabatic barriers.
Q: What does the Zeroth Law of Thermodynamics state?
A: If object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object A is also in thermal equilibrium with object C.
What is the sign convention for work (𝑤) when work is done on a system?
w is positive when work is done on the system, such as stretching a muscle or an elastic band.
Q: What is the sign convention for work (𝑤) when a system does work?
w is negative when a system does work, such as raising a weight.
What is the sign convention for heat (𝑞) when a system heats its surroundings?
q is negative when the system heats its surroundings.
What does a positive value of
𝑤 indicate in a system?
It indicates that work is being done on the system.
Q: What does a negative value of
𝑞 signify?
A: It signifies that the system is losing heat to its surroundings.
Q: What happens to the system’s work sign when gas expansion occurs?
A: The work is negative because the system is doing work.
What is the relationship between work, pressure, and volume change in gas expansion?
W=−Pex ΔV, where
Pex is the external pressure and
ΔV is the change in volume.
How is the volume change (Δ𝑉) calculated in gas expansion?
ΔV=height×area
What is the formula for work in terms of height, area, and external pressure?
W=−hA⋅Pex
where
h is height
A is area
Pex is external pressure.
Q: When does a system perform the maximum work during expansion?
A: Maximum work is performed when the opposing pressure is infinitesimally less than the internal pressure.
Q: Why is the work done by the system on gas expansion negative?
A: Because the system is losing energy to perform work against the external pressure.
Q: When does a system do no work (w=0) during expansion?
A: A system does no work if there is no opposing force during expansion.
Q: What type of process corresponds to maximum work?
A: Maximum work coincides with a reversible change.
Q: Why does a reversible process result in maximum work?
A: Because the system and surroundings remain nearly in mechanical equilibrium, allowing the system to do the most work possible against the opposing pressure.
What is the formula for heat capacity (𝐶)?
C= ΔT/Q
where
q is heat transferred
ΔT is the change in temperature.
Q: How can the quantity of transferred heat (𝑞) be calculated if the heat capacity is known?
q=CΔT, where
C is the heat capacity and
ΔT is the temperature change.
Q: What is the difference between specific heat capacity (𝐶𝑠 ) and molar heat capacity (𝐶𝑚 )?
Cs:
Heat capacity per gram
(JK −1g −1)
Cm:
Heat capacity per mole
(𝐽K−1 mol −1)
What does 𝐶𝑝 represent?
Heat capacity at constant pressure, often used in open systems (e.g., an open beaker).
What does 𝐶𝑣 represent?
Heat capacity at constant volume, used in systems where volume does not change.
Why is knowledge of heat capacity important in thermodynamics?
It allows the calculation of the energy transferred as heat during metabolic or chemical processes.
Q: What is a key feature of a reversible isothermal expansion of a perfect gas?
A: The temperature of the gas remains constant at the beginning and end of the expansion.
Q: Why does the kinetic energy of the gas remain constant during isothermal expansion?
A: Because the speed of gas molecules is a function of temperature, and the temperature remains constant.
Q: What happens to the total energy of a perfect gas during isothermal expansion?
A: The total energy remains constant because it is equal to the kinetic energy, and the potential energy of a perfect gas is negligible.
Q: How is the energy lost as work during isothermal expansion replaced?
A: Heat from the surroundings exactly replaces the energy lost as work, ensuring
q = −w.
Q: What is the equation for work (𝑤) done during the reversible isothermal expansion of a perfect gas?
𝑤 = −𝑞 =𝑛𝑅𝑇 ln(𝑉𝑓/𝑉𝑖)
where
𝑉𝑓 and 𝑉𝑖
are the final and initial volumes
Q: Why does q=−w in isothermal expansion?
Because the heat absorbed from the surroundings balances the work done by the gas, maintaining constant internal energy.
Q: What does the internal energy (
𝑈) of a system include?
A: The total energy (kinetic + potential) of all the atoms, molecules, and ions in the system.
Q: Why is it impossible to directly measure the total internal energy of a system?
A: Because the total energy includes the kinetic and potential energies of all subatomic particles in the system.
Q: How can changes in internal energy (Δ𝑈) be measured?
A: Changes in internal energy can be measured by observing the changes in work and heat during a reaction or physical change.
Q: What is the equation for the change in internal energy (
Δ𝑈) ?
Δ𝑈= 𝑤 + 𝑞
where
𝑤 is the work done and
𝑞 is the heat transferred.
Q: What happens to the internal energy (Δ𝑈) during the isothermal expansion of a perfect gas?
ΔU=0, because the temperature remains constant and no change in internal energy occurs.
Q: Why is the internal energy of a perfect gas independent of the volume it occupies?
A: Because, at a given temperature, only the distance between molecules changes, not their speeds or kinetic energies.
Q: What is the relationship between heat (𝑞) and work (𝑤) during isothermal expansion of a perfect gas?
q=−w; they are equal in magnitude but opposite in sign.
Q: What does it mean that internal energy is a state function?
A: Internal energy is a physical property that depends only on the current state of the system and is independent of the path taken to reach that state.
Q: How does the internal energy of a perfect gas change during isothermal expansion?
A: The internal energy remains constant since the temperature does not change during the expansion.
Q: What does the First Law of Thermodynamics state about isolated systems?
A: Isolated systems can neither do work upon nor heat their surroundings, meaning their internal energies cannot change.
Q: What happens to the internal energy of an isolated system?
A: The internal energy of an isolated system remains constant.
Q: Why do perpetual motion devices fail according to the First Law of Thermodynamics?
A: They fail because the internal energy always drops when they do work, violating the conservation of energy.
Q: What is required for any system that performs work?
A: New sources of energy must be supplied at regular intervals, such as food, petrol, or other energy inputs.
Q: What does the First Law of Thermodynamics imply for energy conservation?
A: Energy cannot be created or destroyed; it can only be transferred or converted from one form to another.
How can ΔU (change in internal energy) be measured in a system with fixed volume?
In a fixed-volume vessel, no expansion work is possible (w=0), so
ΔU=qv , which is the heat generated for the system with fixed volume.
What is the relationship between heat capacity (C) and temperature change (ΔT)?
C= q/ΔT
where
q is the heat transferred and
ΔT is the temperature change.
Q: How is 𝐶𝑣 (heat capacity at constant volume) related to ΔU and temperature change?
𝐶𝑣=Δ𝑈/Δ𝑇
where
ΔU is the change in internal energy and
ΔT is the temperature change
What does the subscript
𝑣 in 𝐶𝑣 represent?
The subscript 𝑣 indicates that the heat capacity is measured at constant volume, where no expansion work occurs.
What happens to the change in internal energy (ΔU) in a fixed-volume system?
The change in internal energy is equal to the heat added to the system ( Δ 𝑈 = 𝑞𝑣) since no work is done.
Q: Why is enthalpy (𝐻) used in biological systems rather than internal energy (𝑈)?
A: Enthalpy is used because most biological systems operate at constant pressure, not constant volume, so adjustments are needed to account for work done by or on the system.
What is the equation for enthalpy (H)?
H=U+pV, where
U is the internal energy,
p is the pressure, and
V is the volume.
How is the change in enthalpy
(Δ𝐻) related to the change in internal energy (Δ𝑈) ?
ΔH=ΔU+Δ(pV).
What is the simplified equation for
Δ𝐻 at constant pressure?
ΔH=ΔU+pΔV, because the pressure is constant.
What is an exothermic process?
An exothermic process is one where energy leaves the system as heat, resulting in q<0 and ΔH<0
What does ΔH=qp represent?
It represents the change in enthalpy (ΔH) being equal to the heat transferred at constant pressure (
𝑞𝑝 ).
What is the equation for heat capacity at constant pressure (
𝐶𝑝 )?
Cp = ΔH/ΔT
where
Δ𝐻 is the change in enthalpy and
ΔT is the temperature change.
Q: How is the heat capacity at constant pressure related to enthalpy change?
A: The heat capacity at constant pressure (𝐶𝑝) is equal to the change in enthalpy (Δ𝐻) divided by the change in temperature (Δ𝑇).
Q: What happens to Δ𝐻 in an exothermic reaction?
In an exothermic reaction,
Δ𝐻 is negative, indicating that heat is released by the system.
What happens to
Δ 𝐻 in an endothermic reaction?
In an endothermic reaction,
Δ𝐻 is positive, indicating that heat is absorbed by the system.
Q: What does Δ𝐻𝑚 represent?
ΔHm is the standard molar enthalpy of a substance, which is the heat content per mole of the substance under standard conditions.
Q: Can substances be in their most stable form under standard conditions?
A: No, substances do not have to be in their most stable form under standard conditions. For example, ice or water vapor can exist at 1 bar and 25°C.
Q: What is the standard state of a pure substance?
A: The standard state of a pure substance is its form at exactly 1 bar of pressure and a temperature of 25°C.
Can a substance exist in more than one phase at a particular temperature and pressure?
Yes, a substance can exist in multiple phases (e.g., solid, liquid, gas) at a particular temperature and pressure, such as ice and water vapor at 1 bar and 25°C.
ΔforwardHo = -ΔreverseHo
ΔforwardHo = -ΔreverseHo
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