Thermodynamics II: Entropy and Enthalpy Quiz

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Questions and Answers

What does the second law of thermodynamics state regarding spontaneous processes?

The entropy of the system decreases.

The entropy of the universe decreases.

The entropy of the universe remains constant.

The entropy of the universe increases. (correct)

How is the total entropy change of the universe calculated?

By summing the entropy changes of the system and surroundings. (correct)

By averaging the entropy changes of the system and surroundings.

By subtracting the entropy of the surroundings from that of the system.

By taking the maximum entropy of the system.

What must be true about the change in entropy, ΔS, in an isolated system?

ΔS is unaffected by the system's equilibrium state.

ΔS can be zero in a spontaneous process.

ΔS must be greater than zero in a spontaneous process. (correct)

ΔS can only be less than zero.

What is necessary for the evaluation of the change in entropy, dS?

A reversible process must be conducted. Signup and view all the answers

Which of the following statements is true regarding the entropy of a system during a reversible process?

It is not affected by the actual path taken. Signup and view all the answers

What does the standard reaction enthalpy (Δ rH) represent?

The difference between the standard molar enthalpies of reactants and products Signup and view all the answers

Which equation is used to predict reaction enthalpy at different temperatures?

H(T1) - H(T2) = C[T2 - T1] Signup and view all the answers

What defines a reversible thermodynamic change?

It can be reversed by an infinitesimal change Signup and view all the answers

Which scenario describes a condition of thermodynamic equilibrium?

Internal and external pressures are equal Signup and view all the answers

Why is it important to know the enthalpy of a reaction at different temperatures?

It can affect the reaction rate and spontaneity Signup and view all the answers

What happens to hot objects in relation to their surroundings?

They cool to the temperature of their surroundings Signup and view all the answers

Which of the following is true about spontaneous processes?

They can occur in a direction determined by natural laws Signup and view all the answers

In the context of biochemical reactions, what would be a reason to analyze enthalpy at various temperatures?

To understand the thermodynamic properties involved Signup and view all the answers

What does the first thermodynamic master equation express in terms of internal energy?

dU = TdS - pdV Signup and view all the answers

What is the relationship expressed by the second master equation?

dH = TdS + VdP Signup and view all the answers

Under conditions of constant pressure, what does the change in Gibbs energy (dG) become?

dG = -SdT Signup and view all the answers

What factor causes the Gibbs energy to fall more steeply with temperature for a gas than for a condensed phase?

The higher entropy of the gas phase Signup and view all the answers

Which of the following describes the phase diagram of a substance?

It depicts the conditions for equilibrium between phases. Signup and view all the answers

What is implied when the Gibbs energy increases due to a rise in pressure?

The Gibbs energy is positively correlated with pressure. Signup and view all the answers

In the context of the Gibbs function, what does the complete differential of G suggest?

dG = Vdp - TdS Signup and view all the answers

Which phase has the least steep slope in terms of Gibbs energy variation with temperature?

Solid phase Signup and view all the answers

Which of the following statements about catalysts is true?

A catalyst affects the forward and backward reaction rates equally. Signup and view all the answers

What is the main consequence of a slight change in the concentration of H+ ions in a biological system?

It can lead to disease or cell damage. Signup and view all the answers

According to Brønsted–Lowry theory, what defines an acid?

An acid is a proton donor. Signup and view all the answers

What equilibrium is always present even in the absence of added acids and bases?

Autoprotolysis equilibrium. Signup and view all the answers

What does the pH scale represent in relation to hydronium ion concentration?

A change in pH by 1 unit represents a 10-fold change in H3O+ concentration. Signup and view all the answers

When ammonia (NH3) acts as a base, what happens in the equilibrium?

It gains protons. Signup and view all the answers

What is the significance of protonation and deprotonation in biochemical reactions?

They are key steps that need quantitative description. Signup and view all the answers

In the given reaction 2H2(g)+ O2(g) ⇌ 2H2O(l), what is implied regarding the reaction conditions?

The reaction can proceed slowly even with high yield potential. Signup and view all the answers

What is the effect of increasing temperature on an endothermic reaction?

It favors the forward reaction. Signup and view all the answers

What happens to the equilibrium constant K when the temperature of an exothermic reaction is increased?

K decreases. Signup and view all the answers

How is heat treated in an endothermic reaction when writing the reaction equation?

As a reactant. Signup and view all the answers

If the change in enthalpy (ΔH) is positive for a reaction, what type of reaction is it?

Endothermic. Signup and view all the answers

In the reaction 2SO2(g) + O2(g) ⇄ 2SO3(g), what is the sign of ΔH if the reaction favors lower temperatures?

Negative. Signup and view all the answers

What is the relationship between Gibbs Free Energy (ΔG) and equilibrium constant (K)?

ΔG = ΔH – TΔS. Signup and view all the answers

Which of the following reactions would have ΔH as negative and be endothermic?

N2O4(g) ⇄ 2NO2(g) Signup and view all the answers

Which statement about the equilibrium constant K is true when temperature changes?

K varies with temperature according to ΔH. Signup and view all the answers

What is the equilibrium constant expression for the reaction 2A ⇄ C + D?

$K = \frac{[C][D]}{[A]^2}$ Signup and view all the answers

If the value of Keq is calculated as 4.1 x 10^-4 for the reaction N2(g) + 3H2(g) ⇄ 2NH3(g), what does this indicate about the equilibrium state?

Reactants are favored at equilibrium Signup and view all the answers

For the reaction 2SO2(g) + O2(g) ⇄ 2SO3(g), what is the correct equilibrium constant expression in terms of partial pressures?

$K_p = \frac{(P_{SO3})^2}{(P_{SO2})^2(P_{O2})}$ Signup and view all the answers

What do ΔHo and ΔSo represent in the equation ΔGo = ΔHo - TΔSo?

Standard enthalpy change and standard entropy change Signup and view all the answers

For the reaction HI(g) ⇄ 1/2H2(g) + 1/2I2(g), how would you express the equilibrium constant Kc?

$K_c = \frac{[H2]^{1/2}[I2]^{1/2}}{[HI]}$ Signup and view all the answers

Which of the following statements about equilibrium constants is true?

Keq values represent the ratio of products to reactants at equilibrium. Signup and view all the answers

In the relationship between free energy change and the equilibrium constant, what does a negative ΔGo value imply?

Products are favored at equilibrium. Signup and view all the answers

What is the relationship between Kc and Kp for a gaseous reaction?

Kp can be calculated from Kc using the ideal gas law. Signup and view all the answers

Study Notes

Thermodynamics: Fundamentals

Thermodynamics describes the macroscopic state of a complex system using a small number of macroscopic variables, such as pressure and temperature, also known as state variables. Thermodynamic potentials are also used.
This subject encompasses a broad range of phenomena, including the efficiency of heat engines and heat pumps, along with chemical processes and biological processes of life.

System, Universe, and Surroundings

The universe comprises the system, the surroundings, and the universe as a whole.
The system is the subject of interest (e.g., a block of iron, a beaker of water, an engine, a human body).
The surroundings are the rest of the universe outside the system.

Types of Systems

Open Systems: Both matter and energy are exchanged between the system and its surroundings. (e.g., an open flask)
Closed Systems: Energy can be exchanged between the system and surroundings, but matter cannot. (e.g., sealed bottle)
Isolated Systems: Neither matter nor energy are exchanged between the system and surroundings. (e.g., a stoppered vacuum flask).

Extensive and Intensive Properties

Extensive Properties: Depend on the amount of matter in the system, e.g., mass, volume.
Intensive Properties: Independent of the amount of matter in the system; e.g., temperature, density.
The density of a substance is an example of an intensive property. For example the density of iron is 8.9kg/cm³ regardless of the mass of the iron block.

State and Path Functions

State Functions: The value depends only on the current state of the substance.
Path Functions: The value depends on the path taken to reach the final state.
Examples of state functions are internal energy (U), enthalpy (H), and entropy (S).
Examples of path functions are heat (q) and work (w).

Laws of Thermodynamics

Zeroth Law: All parts of a system in thermodynamic equilibrium have the same temperature.
First Law: Energy is conserved; it can not be created nor destroyed, it only changes form. The change in the internal energy of a system can only be altered by heat addition (or subtraction) or work done on (or by) the system. (∆U=q+w)
Second Law: Processes tend to proceed in a direction that increases the total entropy of the universe involved. (∆Suniverse > 0)
Third Law: The entropy of a perfect crystal approaches zero as the temperature approaches absolute zero (0K).

Thermodynamic Equilibrium

A state of equilibrium is reached when the internal pressure and external pressure are equal.
Heat is an example of energy transfer that is proportional to temperature difference.
Work is a transfer of energy that causes a change of motion or position.

Other Concepts

Internal Energy (U): The total of all microscopic energies within a system.
Heat (q): Energy transfer due to a temperature difference.
Work (w): Form of energy transfer associated with a change of position or motion.
Temperature: A measure of the average kinetic energy of the molecules in a substance.

State Equation of an Ideal Gas

pV = nRT, where p is pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is temperature.

Temperature

Measured in Kelvin (K).
The boiling point of pure water at standard pressure is 373.15K.
The freezing point of pure water at standard pressure is 273.15K.

Thermochemical properties of fluids

The properties of enthalpy and entropy depend on the pressure (not in the case of ideal gases), the volume of the substance, and the pathway.

Specific Heat Capacity

The amount of heat required to change the temperature of a substance by a given amount.

Calculating Enthalpy Changes

Enthalpy changes in chemical reactions can be derived when reactants and products are at a known temperature and pressure.

Hess's Law

The enthalpy change for a reaction is independent of the pathway.

Reversible and Irreversible Processes

A reversible process can be reversed by an infinitesimal change in conditions, as in equilibrium.
Irreversible processes proceed in a specific direction and cannot easily be reversed.

Entropy

A thermodynamic measure of disorder in a system.
∆S is the Change in entropy.
Entropy changes in chemical processes can be determined quantitatively at given temperatures and pressures.

The Gibbs Function

A useful function to assess whether a process can occur spontaneously at a constant temperature and pressure. -For the reaction to proceed spontaneously at a given temperature, ∆G < 0,∆G= ∆H − T∆S, where H is Enthalpy change and S entropy change.

Phase Diagrams

Illustrate conditions of temperature and pressure under which various phases of a substance are stable.

Vapour Pressure

The pressure exerted by a vapour in equilibrium with a liquid or solid at a given temperature.

Raoult's Law

Ratio of the partial vapor pressure of a liquid in a mixture relative to the vapor pressure as a pure substance.

Henry's Law

The partial vapor pressure of a solute in a mixture is proportional to its mole fraction where the proportionality constant is the vapor pressure of the pure solute.

Activities

Activity is defined as the effective concentration of a substance in solution.
The activity coefficient is the correction for interactions between solute, or different molecules.

The Free Energy of Mixing

The Gibbs energy change when two or more components are mixed.

Reaction Rates

Rate of a reaction can be determined experimentally.
Rate laws show the relationship between reaction rate and concentrations of reactants and/or products.

Rate Order

The exponent in a rate law equation tells which reactant it depends on.

Collision Theory & Concentration

For a reaction to occur, collisions between molecules need to occur with sufficient energy and proper orientation.

Activation Energy

The activation energy is minimum energy necessary to convert reactants to products in a reaction.

Arrhenius Equation

Shows the relationship between reaction rate or constant, activation energy and temperature -The Arrhenius equation allows calculation of rate constants for reaction at different temperatures.

Reaction Mechanisms

A series of steps that depict a chemical reaction occurring.
Elementary steps in a reaction mechanism may be single or multiple molecules.

Rate-Determining Step

-In a reaction mechanism, the slowest step (with the highest activation energy) is the rate-determining step.

Catalysis

A catalyst changes the rate of a reaction, without being consumed in the overall reaction.
Catalysts lower the activation energy.

Ionic Equilibria

Proton transfer equilibria: Reactions describing proton transfer between different molecules in aqueous solutions.
H3O+ and OH−: The hydronium and hydroxide ions play crucial roles in determining acidity and basicity.
pH: A measure of the concentration of H3O+ ions which is expressed in terms of the pH.
pOH: A measure of the concentration of OH− ions which is expressed in terms of the pOH.

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Description

Test your understanding of the second law of thermodynamics and its implications for spontaneous processes. This quiz covers key concepts such as entropy, enthalpy changes, and the characteristics of reversible processes. Assess your knowledge of thermodynamic principles relevant to biochemical reactions and temperature effects.