Thermodynamics Quiz: Principles and Concepts
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Questions and Answers

What does the first law of thermodynamics imply about energy in a closed system?

  • The total energy of a closed system remains constant. (correct)
  • Energy can only change forms, but cannot be transferred outside the system.
  • Energy loss is inevitable in all physical processes.
  • Energy can be created provided it is transformed from one form to another.

Which of the following quantities represents heat transfer at constant pressure?

  • Heat Capacity (correct)
  • Gibbs Energy
  • Internal Energy
  • Specific Heat Capacity

In the context of the second law of thermodynamics, what does an increase in entropy signify?

  • The overall energy of the universe is being conserved.
  • Energy dispersion is increasing, leading to irreversible processes. (correct)
  • Energy is being converted into work with no losses.
  • There is a decrease in the available energy within the universe.

Which statement correctly distinguishes between thermodynamics and chemical kinetics?

<p>Thermodynamics quantifies heat and energy but not reaction rates. (D)</p> Signup and view all the answers

What does Gibbs free energy help to predict about a chemical reaction?

<p>The feasibility and direction of a spontaneous reaction. (A)</p> Signup and view all the answers

Which of the following best defines internal energy?

<p>The total energy associated with all types of energy in a substance. (C)</p> Signup and view all the answers

What is represented by the symbol 𝑄 in thermodynamics?

<p>Heat absorbed or released during a process. (A)</p> Signup and view all the answers

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

<p>The total change in internal energy is the sum of heat and work. (B)</p> Signup and view all the answers

What does the third law of thermodynamics state about the entropy of a perfect crystal at zero Kelvin?

<p>The entropy is zero. (A)</p> Signup and view all the answers

What does the symbol $H$ represent in thermodynamics?

<p>The sum of internal energy and pressure-volume work. (C)</p> Signup and view all the answers

In which type of reaction is the enthalpy change ($ riangle H$) positive?

<p>Endothermic reactions (A)</p> Signup and view all the answers

Which equation correctly represents the entropy change ($ riangle S$) during a phase change?

<p>$ riangle S = rac{ riangle H_{fusion}}{T_{m}}$ (D)</p> Signup and view all the answers

Which statement accurately describes the relationship between microstates and entropy?

<p>Higher entropy corresponds to a higher number of available microstates. (A)</p> Signup and view all the answers

What is the main focus of thermochemical equations?

<p>Descriptions of changes in both matter and energy. (A)</p> Signup and view all the answers

What does $k_B$ represent in the Boltzmann equation?

<p>The Boltzmann constant. (A)</p> Signup and view all the answers

What is the significance of the expression $q_{rev}$ in calculating entropy change?

<p>It represents the reversible heat added or removed from a system. (C)</p> Signup and view all the answers

At which temperature does the reaction of NH4NO3 switch from being thermodynamically favorable to unfavorable?

<p>234 K (B)</p> Signup and view all the answers

What is the correct expression for the reaction quotient Q?

<p>[C]^x [D]^y / [A]^m [B]^n (C)</p> Signup and view all the answers

Which relationship connects Gibb’s energy and the equilibrium constant K?

<p>ΔG = -RT ln K (D)</p> Signup and view all the answers

What does the heat capacity of a material relate to?

<p>Change in enthalpy and entropy as a function of temperature (D)</p> Signup and view all the answers

What is the specific heat capacity of water in J K−1 g−1?

<p>4.184 (D)</p> Signup and view all the answers

When is the reaction quotient Q equal to the equilibrium constant K?

<p>At equilibrium (D)</p> Signup and view all the answers

What is the temperature unit used in the Gibb's energy equation?

<p>Kelvin (B)</p> Signup and view all the answers

What kind of parameter is heat capacity in thermodynamics?

<p>A thermodynamic parameter (C)</p> Signup and view all the answers

What is the correct formula to calculate the change in Gibb's energy (ΔG)?

<p>ΔG = ΔH - TΔS (B)</p> Signup and view all the answers

If a reaction has a negative Gibb's energy, what can be inferred about the reaction's spontaneity?

<p>The reaction is thermodynamically favorable. (C)</p> Signup and view all the answers

In the calculation of standard molar entropy (ΔSrxn), what is the correct expression for ΔSrxn based on given reaction data?

<p>ΔSrxn = S(H2O) - S(H2) - S(O2) (B)</p> Signup and view all the answers

Which of the following describes the relationship between bond formation and energy?

<p>The formation of bonds is exothermic, releasing energy. (D)</p> Signup and view all the answers

How does temperature affect Gibb's energy when ΔH and ΔS have the same sign?

<p>Gibb's energy can switch from spontaneous to non-spontaneous with changing temperature. (C)</p> Signup and view all the answers

In the context of Hess's law, what is essential for determining the energy changes in a reaction?

<p>Only the initial and final states must be considered. (A)</p> Signup and view all the answers

What is the bond dissociation energy (D) in the context of reaction energy changes?

<p>The energy required to break bonds in the reactants. (B)</p> Signup and view all the answers

What important thermodynamic characteristic is indicated by a reaction occurring at a switching temperature?

<p>It affects whether the reaction will be spontaneous or non-spontaneous. (A)</p> Signup and view all the answers

What is the primary reason for considering heat capacities when quantifying change in enthalpy as a function of temperature?

<p>To determine the difference in heat capacities of products and reactants (B)</p> Signup and view all the answers

Which equation describes the fundamental relationship in terms of an infinitesimal change in enthalpy?

<p>dH = TdS + VdP (D)</p> Signup and view all the answers

What is the formula for the change in entropy of an expanding gas?

<p>ΔS = nRT ln(Vf / Vi) (B)</p> Signup and view all the answers

What does the integral form of heat capacity ΔCp involve when relating enthalpy changes?

<p>The difference between specific heat capacities of the components during a reaction (C)</p> Signup and view all the answers

In the ideal gas law, what does 'R' represent?

<p>The universal gas constant in J K^-1 mol^-1 (C)</p> Signup and view all the answers

What is the implication of using differential forms of expressions in thermodynamics?

<p>They allow precise calculations of infinitesimal changes in state functions (A)</p> Signup and view all the answers

How does the ideal gas law relate volume and pressure to temperature?

<p>By using the average kinetic energy of gas particles (C)</p> Signup and view all the answers

Which variable represents change in internal energy in thermodynamics?

<p>dU (D)</p> Signup and view all the answers

What is the enthalpy change for the reverse reaction of the combustion of hydrogen, scaled by a factor of 2?

<p>482 kJ mol−1 (A)</p> Signup and view all the answers

Which of the following correctly combines the combustion of carbon and the combustion of hydrogen?

<p>C(s) + 2 H2 O (g) −−−→ CO2 (g) + 2 H2 (g) Δ𝐻 = 89 kJ mol−1 (A)</p> Signup and view all the answers

How are the Gibbs energy changes for a reaction calculated from the standard values?

<p>Δ𝐺𝑟𝑥𝑛 = Σ(𝜈Δ𝐺 𝑓 (products)) − Σ(𝜈Δ𝐺 𝑓 (reactants)) (B)</p> Signup and view all the answers

What is the significance of the terms Δ𝐻, Δ𝑆, and Δ𝐺 in thermodynamic equations?

<p>They represent energy changes associated with reactions. (D)</p> Signup and view all the answers

According to Hess’s law, how is the total enthalpy change for a reaction determined?

<p>It is the sum of all individual enthalpy changes. (B)</p> Signup and view all the answers

Which of the following correctly states the standard conditions for enthalpy, entropy, and Gibbs energy changes?

<p>298 K and 1 bar pressure (C)</p> Signup and view all the answers

The thermochemical equation for the combustion of carbon yields an enthalpy change of what value?

<p>-393 kJ mol−1 (D)</p> Signup and view all the answers

When combining thermochemical equations, which of the following statements is true?

<p>The enthalpy changes are multiplied by the stoichiometric coefficients. (B)</p> Signup and view all the answers

Flashcards

Internal Energy (U)

The total energy of a system, including all forms of energy like kinetic and potential energy.

Enthalpy (H)

The energy transferred as heat during a process at constant pressure.

Entropy (S)

A measure of the randomness or disorder of a system.

Heat (q)

The energy transferred as heat in a process.

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Work (w)

The energy transferred as work in a process.

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First Law of Thermodynamics

The first law of thermodynamics states that energy cannot be created or destroyed, only transformed from one form to another.

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Second Law of Thermodynamics

The second law of thermodynamics states that the entropy of the universe always increases in a spontaneous process.

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Third Law of Thermodynamics

The third law of thermodynamics states that the entropy of a perfectly crystalline substance at absolute zero is zero.

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Enthalpy Change (ΔH)

The heat released or absorbed by a system under constant pressure during a chemical or physical process.

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Exothermic Reaction

A process that releases heat to the surroundings.

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Endothermic Reaction

A process that absorbs heat from the surroundings.

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Entropy Change (ΔS)

The mathematical product of the reversible heat change and the inverse of the temperature. ΔS = q_rev/T

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Enthalpy Change of Reaction (ΔHrxn)

The change in enthalpy for a reaction, calculated by subtracting the sum of enthalpy of formation of reactants from the sum of enthalpy of formation of products.

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Standard Enthalpy of Formation (ΔHf)

A reaction's enthalpy change when one mole of a substance is formed from its elements in their standard states.

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Entropy Change of Reaction (ΔSrxn)

The change in entropy for a reaction, calculated by subtracting the sum of entropy of formation of reactants from the sum of entropy of formation of products.

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Standard Entropy of Formation (ΔSf)

A reaction's entropy change when one mole of a substance is formed from its elements in their standard states.

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Gibbs Free Energy Change of Reaction (ΔGrxn)

The change in Gibbs free energy for a reaction, calculated by subtracting the sum of Gibbs free energy of formation of reactants from the sum of Gibbs free energy of formation of products.

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Standard Gibbs Free Energy of Formation (ΔGf)

A reaction's Gibbs free energy change when one mole of a substance is formed from its elements in their standard states.

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Manipulating Thermochemical Equations

The process of manipulating thermochemical equations to obtain the desired enthalpy change for a specific reaction.

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Hess’s Law

A law that states that the total enthalpy change for a reaction is the sum of enthalpy changes for each step, regardless of the number of steps involved.

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Standard Molar Entropy Change (ΔSrxn)

The change in entropy for a reaction, calculated by subtracting the sum of the entropies of the reactants from the entropy of the products.

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Bond Dissociation Energy Approach

A way to calculate the enthalpy change of a reaction based on the difference in bond dissociation energies of the products and reactants.

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Gibbs Free Energy (ΔG)

A thermodynamic potential representing the maximum amount of work a system can do at constant temperature and pressure.

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Thermodynamically Favorable Reaction

A process is thermodynamically favorable and spontaneous if its Gibbs free energy change is negative, and unfavorable if its Gibbs free energy change is positive.

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Enthalpy Change (ΔH) for a Reaction

The enthalpy change of a reaction is the sum of the bond dissociation energies of the bonds broken minus the sum of the bond dissociation energies of the bonds formed.

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Gibbs Free Energy Change Equation (ΔG = ΔH - TΔS)

The change in Gibbs free energy can be calculated using the formula: ΔG = ΔH - TΔS. It helps determine the spontaneity of a reaction.

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Fundamental Thermodynamic Relationship

The fundamental thermodynamic relationship defines the change in internal energy (dU) as the sum of the reversible heat transfer (TdS) and the work done on the system (-PdV).

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Entropy Change of an Expanding Gas

For an expanding gas, the change in entropy (ΔS) is directly proportional to the natural logarithm of the ratio of final volume (Vf) to initial volume (Vi), multiplied by the number of moles (n) and the ideal gas constant (R).

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Ideal Gas Law

The relationship between pressure, volume, temperature, and number of moles for an ideal gas. It states that the product of pressure (P) and volume (V) is proportional to the product of the number of moles (n) and the ideal gas constant (R) multiplied by the temperature (T).

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Enthalpy Change as a Function of Temperature

The change in enthalpy of a reaction (ΔHrxn) at a specific temperature (T2) can be calculated by adding the enthalpy change at a reference temperature (T1) to the integral of the change in heat capacity (ΔCp) with respect to temperature from T1 to T2.

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Enthalpy Change at Constant Pressure

The enthalpy change at constant pressure (ΔH) is the difference between the enthalpies of the final state (Hf) and the initial state (Hi).

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Entropy Change at Constant Temperature

The change in entropy (ΔS) at constant temperature (T) is calculated by dividing the reversible heat change (q_rev) by the temperature (T).

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Enthalpy Change

The change in enthalpy of a reaction (ΔHrxn) is the difference between the enthalpies of formation of the products and the reactants.

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Entropy Change

The change in entropy (ΔSrxn) is the difference between the entropies of formation of the products and the reactants.

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Thermodynamically Favorable/Unfavorable Transition

The point at which a reaction transitions from being thermodynamically favorable (spontaneous) to unfavorable (non-spontaneous), determined by the point where the Gibbs Free Energy change becomes zero.

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Reaction Quotient (Q)

A measure of the relative amounts of reactants and products present in a reversible reaction at a given time. It helps predict which direction a reaction will shift to reach equilibrium.

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Chemical Equilibrium

The state where the forward and reverse reaction rates are equal, resulting in no net change in the concentrations of reactants and products. It's defined by the equilibrium constant (K).

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Equilibrium Constant (K)

A constant that describes the relative amounts of reactants and products at equilibrium. It is temperature-dependent and indicates the extent to which a reaction proceeds to completion.

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Gibbs Free Energy Change (ΔG)

The free energy change associated with a reaction at equilibrium, reflecting the maximum amount of useful work that can be obtained from the reaction.

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Heat Capacity

The amount of heat required to raise the temperature of a substance by one degree Celsius. It's an important factor in calorimetry and understanding energy changes in materials.

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Thermochemistry

The branch of chemistry dealing with the study of energy changes in chemical reactions and physical transformations.

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Calorimetry

A technique used to measure the amount of heat absorbed or released during a chemical or physical process. It's based on the principle of heat transfer and involves measuring temperature changes.

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Study Notes

Thermodynamics

  • Thermodynamics is a branch of science that quantifies the transfer of heat, work, and energy
  • It is used in chemistry to quantify heat changes during reactions to determine if a reaction is feasible
  • Chemical kinetics focuses on reaction rates, distinct from thermodynamics

Laws of Thermodynamics

  • First Law: Energy cannot be created or destroyed. ΔU = q + w, where ΔU is internal energy, q is heat, and w is work
  • Internal energy is the sum of all possible energies in a substance
  • Second Law: The entropy of the universe always increases. S = entropy and ΔSuniverse ≥ 0;
  • Entropy is a measure of the dispersion of energy in a system
  • Third Law: For a perfect crystal at zero Kelvin, the entropy of the system is zero. S(0K) = 0

Enthalpy and Entropy

  • Enthalpy (H) is the sum of a system's internal energy (U) and the product of its pressure (P) and volume (V). H = U + PV
  • Enthalpy change (ΔH) represents heat absorbed or released at constant pressure.
  • ΔH = qp

Entropy Change (ΔS)

  • ΔSrev = qrev/T
  • ΔS represents the entropy change associated with a change of phase and can be calculated using the enthalpy change (ΔHfusion) and melting point (Tm). ΔS = ΔHfusion / Tm

Standard Enthalpy, Entropy and Gibbs Energy

  • Standard enthalpy change (ΔHorxn), standard entropy change (ΔSorxn), and standard Gibbs free energy change (ΔGorxn) can be calculated from the changes of the reactants and products
    • ΔHorxn = Σ νΔHof (products) - Σ νΔHof (reactants)
    • ΔSorxn = Σ νSof (products) - Σ νSof (reactants)
    • ΔGorxn = Σ νΔGof (products) - Σ νΔGof (reactants)
  • where ν is the stoichiometric coefficient, and ΔHof, Sof and ΔGof are the standard molar enthalpy, entropy, and Gibbs free energy of formation, respectively,

Gibbs Free Energy (G)

  • Gibbs free energy (G) is related to enthalpy (H), entropy (S), and temperature (T) by the equation: ΔG = ΔH - TΔS.
  • If ΔG is negative, the reaction is thermodynamically favorable
  • If ΔG is positive the reaction is thermodynamically unfavorable
  • If ΔG = 0 the reaction is at equilibrium.
  • Chemical equilibrium is when there is no net change in the amounts of reactants and products
  • Reaction Quotient (Q) is used to quantify the relative amounts of reactants and products in a reaction.
  • Q = [C]c[D]d / [A]a[B]b; where a,b,c,d are stoichiometric coefficients

Heat Capacities

  • The heat capacity is the amount of heat needed to raise the temperature of a substance by one degree
  • Heat capacity (Cp) is defined at constant pressure
  • ΔH=integral Ti->Tf

Ideal Gases

  • The ideal gas law (PV = nRT) relates the pressure (P), volume (V), temperature (T), number of moles (n), and the ideal gas constant (R) of a gas.
  • Entropy change of an expanding gas (ΔS): ΔS = nR ln(Vf /Vi)

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Test your understanding of key principles in thermodynamics with this quiz. Questions cover the first and second laws of thermodynamics, Gibbs free energy, and the distinction between thermodynamics and chemical kinetics. Perfect for students studying physics or chemistry.

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