Thermodynamics Overview Quiz
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Questions and Answers

Which statement correctly describes the 2nd law of thermodynamics?

  • Energy can only be converted from one form to another.
  • All systems reach equilibrium simultaneously.
  • Everything tends toward maximum disorder. (correct)
  • Energy can be created from nothing.

    • In the context of the ideal gas law, what does the variable 'R' represent?

  • The ideal gas constant (correct)
  • Number of molecules in the system
  • Pressure of the gas
  • Volume in cubic meters

    • What does the first law of thermodynamics imply about energy changes in an isolated system?

  • Energy can be created if needed.
  • Energy can only be transferred as heat.
  • All energy changes sum to zero. (correct)
  • Energy changes sum to a positive value.

    • Which of the following is NOT considered an extensive state function?

    <p>Temperature</p> Signup and view all the answers

    What is the formula that expresses the relationship of pressure, volume, number of moles, and temperature in an ideal gas?

    <p>pV = nRT</p> Signup and view all the answers

    If a system experiences a negative q value, what does this indicate about the heat exchange?

    <p>The system is losing heat to the surroundings.</p> Signup and view all the answers

    What does the equation ΔU = q + w represent in thermodynamics?

    <p>Change in internal energy equals heat added and work done.</p> Signup and view all the answers

    How can energy exchange occur in a thermodynamic system?

    <p>Through both heat and work.</p> Signup and view all the answers

    What is the implication of the 3rd law of thermodynamics regarding temperature?

    <p>Disorder increases with temperature.</p> Signup and view all the answers

    If a system does work on the surroundings, how is this represented in terms of the work done (w)?

    <p>w is negative.</p> Signup and view all the answers

    What happens during an isochoric process?

    <p>No work is done by or on the system.</p> Signup and view all the answers

    Which equation represents the change in internal energy at constant pressure?

    <p>ΔUp = qp + wp</p> Signup and view all the answers

    How is enthalpy (H) defined in thermodynamics?

    <p>H = U + pV</p> Signup and view all the answers

    According to Hess's law, how can the total enthalpy change be determined?

    <p>By performing the reaction in a series of steps and adding the changes.</p> Signup and view all the answers

    What characterizes an endothermic reaction?

    <p>ΔH is positive, absorbing heat from surroundings.</p> Signup and view all the answers

    What does the Boltzmann distribution describe?

    <p>The energy distribution among particles in bulk systems.</p> Signup and view all the answers

    In the context of the second law of thermodynamics, what must happen for a process to occur?

    <p>The final state must be more disordered.</p> Signup and view all the answers

    What factor affects the ratio of molecules at different energy levels in the Boltzmann distribution?

    <p>The difference in energy levels and temperature.</p> Signup and view all the answers

    Which definition accurately describes the work done due to expansion in thermodynamics?

    <p>wp = -pΔV</p> Signup and view all the answers

    When a gas undergoes an expansion, what is the sign of ΔV?

    <p>ΔV is positive.</p> Signup and view all the answers

    What happens to the disorder in a system as temperature increases?

    <p>It increases.</p> Signup and view all the answers

    Which equation correctly represents the efficiency of a Carnot engine?

    <p>Eff = 1 - TC/TH</p> Signup and view all the answers

    Which statement accurately describes the Gibbs free energy and its change?

    <p>Negative ΔG indicates a spontaneous process.</p> Signup and view all the answers

    What ratio defines the entropy change (ΔS) in a thermodynamic process?

    <p>ΔS = q/T</p> Signup and view all the answers

    In ideal gas behavior, which equation describes the relationship of pressure, volume, and temperature?

    <p>pV = nRT</p> Signup and view all the answers

    Which of the following indicates a system at equilibrium?

    <p>Rates of the forward and backward reactions are equal.</p> Signup and view all the answers

    What is the effect of performing work on a thermodynamic system?

    <p>It can require the release of heat to maintain energy balance.</p> Signup and view all the answers

    What happens to the Gibbs free energy when reactants are added to a system at equilibrium?

    <p>ΔG becomes negative.</p> Signup and view all the answers

    For a spontaneous reaction, what must occur in terms of chemical potentials?

    <p>The sum of weighted chemical potentials must decrease.</p> Signup and view all the answers

    When considering ideal behavior in gas mixtures, what does the term 'partial pressure' refer to?

    <p>The pressure exerted by an individual gas in the mixture.</p> Signup and view all the answers

    In the context of the Carnot cycle, what is true about heat energy flow?

    <p>Some portion of heat energy is always lost as qC.</p> Signup and view all the answers

    Which statement is correct regarding ideal solutions?

    <p>Interactions are identical to those in the standard state.</p> Signup and view all the answers

    What happens to the ΔG when a system has a ΔG < 0?

    <p>The process is spontaneous.</p> Signup and view all the answers

    Study Notes

    Extensive State Function

    • Extensive state functions depend on the size of the system
    • Temperature and pressure are extensive state functions
    • Examples of state functions include mass, volume, energy
    • Most thermodynamic quantities are extensive state functions

    Path Function

    • A path function depends on the path taken
    • Heat and work are path functions

    Zeroth Law of Thermodynamics

    • If two systems are at equilibrium with a third system then they are also at equilibrium with each other
    • If A ⇌ B and B ⇌ C then A ⇌ C

    First Law of Thermodynamics

    • Energy cannot be created or destroyed, only converted from one form to another
    • Energy changes in an isolated system sum to zero
    • Internal energy is the sum of kinetic and potential energies

    Second Law of Thermodynamics

    • Everything tends toward maximum disorder
    • Disorder increases with temperature

    Third Law Of Thermodynamics

    • Disorder increases with temperature
    • The entropy of a perfect crystal at absolute zero is zero

    Ideal Gas

    • The ideal gas is a simple thermodynamic system to study
    • An ideal gas has particles that negligibly interact and are small compared to the spaces between them

    Ideal Gas Law

    • pV = nRT
    • p is pressure in Pascals (N/m2)
    • V is volume in m3
    • n is the number of moles of gas
    • R is the molar gas constant (8.31 m2 kg s-2 K-1 mol-1)
    • T is the temperature in Kelvin

    First Law of Thermodynamics Summary

    • Energy cannot be created or destroyed
    • The internal energy is defined as U
    • The change in internal energy (ΔU) is Ufinal - Uinitial
    • For an isolated system, ΔU = 0
    • For a closed system the energy gained by the system comes from the surroundings

    Work and Heat

    • q is the heat exchanged between the system and the surroundings
    • Work (w) is the work done on the system by the surroundings

    Heat

    • Heat is the transfer of energy due to a temperature difference
    • Positive heat is heat from surroundings to system
    • Negative heat is heat from system to surroundings

    Work

    • Positive work is work done on the system by the surroundings
    • Negative work is work done by the system on the surroundings
    • There are many kinds of work including: mechanical, electrical, and expansion

    Isochoric Process

    • In an isochoric process, the volume is constant
    • No work is done by the system
    • The energy change is only due to heat

    Isobaric Process

    • Isobaric processes occur at constant pressure
    • Work is done by the system
    • The change in internal energy is equal to the heat transferred plus the work done

    Enthalpy

    • Enthalpy (H) is defined as U + pV
    • Enthalpy change (ΔH) is the change in internal energy due to non-expansive work
    • The question is how much of ΔH can be captured to do useful work

    Enthalpy as a State Function

    • Enthalpy can be measured directly if ΔH = qp
    • Hess’s law of constant heat summation allows for calculation of enthalpy change for a series of steps
    • Enthalpy is an extensive state function affected by the size of the system
    • Reactions with a positive ΔH are endothermic
    • Reactions with a negative ΔH are exothermic

    Boltzmann Distribution

    • Bulk systems are made of a large number of molecules
    • Thermal collisions allow for energy exchange between molecules
    • Not all molecules have the same energy
    • Energy is distributed randomly over all energy levels
    • The Boltzmann distribution: ni/nj = exp(-(Ei-Ej)/kBT)
    • The ratio of the number of molecules with energies Ei and Ej depends on temperature and the energy difference
    • Lower energy levels are always more populated

    Maxwell-Boltzmann Distribution

    • Applies to translational levels
    • Particles can move in three dimensions
    • Temperature increases the average speed of molecules

    Spontaneous Reactions

    • A process will happen if the final state is more disordered than the initial state
    • Particles can occupy different energy levels
    • More thermal energy in the system allows for particles to occupy higher energy levels
    • Disorder increases with temperature

    Carnot Cycle

    • A Carnot engine or cycle is an example of a cyclic reversible process
    • The work done is related to the heat transfer
    • Work done (w) = qH - qC
    • Efficiency (Eff) = w/qH
    • Efficiency is always less than 100%
    • For a Carnot cycle Eff = 1 - TC/TH

    Entropy

    • Entropy (S) is a measure of disorder
    • Entropy is related to the microscopic states of a system
    • S = kblnΩ
    • Entropy increases with heat release
    • Entropy decreases with work

    Gibbs Free Energy

    • The Gibbs free energy (G) is the available energy for doing work
    • G = H - TS
    • ΔG = ΔH - TΔS
    • Negative ΔG = spontaneous process
    • Positive ΔG = non-spontaneous process
    • ΔG = 0 → equilibrium

    Chemical Potential

    • Chemical potential (μ) is an intensive state function
    • μ = G/n
    • Δμ = ΔG/Δn
    • This allows us to deal with open systems where transfer of matter as well as energy occur

    Spontaneous Reactions

    • For a reaction to be spontaneous, the chemical potential of the products must be less than the chemical potential of the reactants

    Chemical Potential of a Pure Ideal Gas

    • For a pure ideal gas: μ = μo + RTln(p/po)
    • We can apply this equation to a component in a mixture of pure gases
    • For a gas mixture: μ = μo + RTln(px/pxo)

    Chemical Potential for a Multi-Component System

    • G = n1μ1 + n2μ2 …

    ΔG for a reaction

    • ΔG = μx1Δnx1 + μx2Δnx2 …
    • We can combine this equation with the chemical potential equation to get an equation for ΔG in terms of [products] and [reactants]
    • For a reaction aA + bB → cC + dD: ΔG = ΔGo + RTln([C]c × [D]d)/( [A]a × [B]b)

    Mass Action Ratio and Equilibrium Constants

    • The mass action ratio (Γ) is the ratio of products to reactants at any given moment
    • ΔG = ΔGo + RTlnΓ
    • At equilibrium ΔG = 0
    • ΔGo = -RTlnKeq
    • ΔG = RTln(Γ/Keq)
    • If Γ < Keq, the reaction is spontaneous
    • If Γ > Keq, the reaction requires energy to happen

    Ideal vs. Non-Ideal Behavior

    • Ideal gases: The only interactions happen upon collisions
    • Ideal solutions: Interactions between molecules are the same as in the standard state
    • Non-ideal behavior: Interactions modify the distribution of molecules

    Activity

    • Activity (ax) is the effective concentration
    • ax = γx[x]
    • Where γx is the activity coefficient of x under those conditions
    • μx = μxo + RTln(ax/axo)

    Summary

    • Thermodynamics is the study of energy changes
    • The total energy of the system never changes
    • The 1st law states that energy is conserved

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    Description

    Test your understanding of key concepts in thermodynamics, including extensive and path functions, the laws of thermodynamics, and the concept of entropy. This quiz covers essential topics that define how energy and systems interact in thermal processes.

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