Chem 175 - Chapter 18 Chemical Thermodynamics

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Questions and Answers

What is Chemical Thermodynamics?

Study of how heat and work are involved in chemical reactions and physical changes.

What are Spontaneous Processes?

Processes that happen under indicated conditions.

What are Non-spontaneous Processes?

Processes that do not happen under indicated conditions.

What is the 1st Law of Thermodynamics?

Total energy of the universe is constant; energy is neither created nor destroyed, but can be transferred. Signup and view all the answers

What is the 2nd Law of Thermodynamics?

Spontaneous processes always result in an overall increase of entropy. Signup and view all the answers

What is Entropy (S)?

Measure of degree of disorder or randomness in a system. Signup and view all the answers

An increase in temperature increases the KE, which ________ the entropy.

increases Signup and view all the answers

What are Microstates?

Number of energetically equivalent arrangements possible for the system. Signup and view all the answers

What is a Macrostate?

Set of energetically equivalent microstates. Signup and view all the answers

What is the 3rd Law of Thermodynamics?

Entropy of a pure, perfectly ordered, crystalline substance at absolute zero is zero. Signup and view all the answers

What is the equation for ∆S° rxn?

∆S° rxn = Σm[S°(products)] - Σn[S°(reactants)] Signup and view all the answers

What is the equation for ∆S univ?

∆S univ = ∆S sys + ∆S surr Signup and view all the answers

What are Isothermal Processes?

Processes with no temperature change in surroundings. Signup and view all the answers

The effect of entropy change of the system on entropy of surroundings is smaller at ___ temps than _ temps.

higher, lower Signup and view all the answers

At ____ temps, surroundings have higher KE and the release of heat energy by the system will increase that KE by a lower % than at _ temps.

higher, lower Signup and view all the answers

In an exothermic reaction, the q sys ___ 0.

<blockquote> </blockquote> Signup and view all the answers

What is Gibb's Free Energy, G?

State function defined in terms of the enthalpy, entropy, and temperature of the system. Signup and view all the answers

What is Standard Free Energies of Formation, ∆Gf°?

Free energy change in the formation of a substance from its elements in their standard states. Signup and view all the answers

When ∆H < 0, ∆S > 0, and -T∆S < 0, the reaction is _______________.

Spontaneous at all temps Signup and view all the answers

When ∆H > 0, ∆S < 0, and -T∆S > 0, the reaction is _______________.

Nonspontaneous at all temps Signup and view all the answers

When ∆H < 0, ∆S < 0, and -T∆S > 0, the reaction is _______________.

Spontaneous at low temps, Nonspontaneous at high temps Signup and view all the answers

When ∆H > 0, ∆S > 0, and -T∆S < 0, the reaction is _______________.

Spontaneous at high temps, Nonspontaneous at low temps Signup and view all the answers

∆S is positive when the distribution becomes more or less equally distributed.

True Signup and view all the answers

Arrange the compounds from highest to lowest standard molar entropy, Sº:

CH3OH = Highest O2 = Middle N2 = Lowest Signup and view all the answers

How is the entropy of Ar affected when it changes from liquid to gas?

increases Signup and view all the answers

How is the entropy of Cu affected when it changes from 300K to 800K?

increases Signup and view all the answers

How is the entropy of Fe affected when it changes from 250K to 25K?

decreases Signup and view all the answers

What statement about the spontaneity and rate of a reaction is true?

The spontaneity of a reaction is not necessarily related to the rate of a reaction. Signup and view all the answers

Which process is necessarily driven by an increase in the entropy of the surroundings?

The freezing of water Signup and view all the answers

Is a cup of hot coffee cooling to room temperature spontaneous or nonspontaneous?

spontaneous Signup and view all the answers

Is iron rusting in moist air spontaneous or nonspontaneous?

spontaneous Signup and view all the answers

Is water being separated into H2 and O2 gas at 25°C spontaneous or nonspontaneous?

nonspontaneous Signup and view all the answers

Is iron metal being extracted from iron ore spontaneous or nonspontaneous?

nonspontaneous Signup and view all the answers

Is perfume molecules spreading out to fill the entire room spontaneous or nonspontaneous?

spontaneous Signup and view all the answers

What is the classification of phase change from solid to liquid?

ΔH = + & ΔS = + Signup and view all the answers

What is the classification of phase change from liquid to gas?

ΔH = + & ΔS = + Signup and view all the answers

What is the classification of phase change from solid to gas?

ΔH = + & ΔS = + Signup and view all the answers

What is the classification of phase change from liquid to solid?

ΔH = - & ΔS = - Signup and view all the answers

What is the classification of phase change from gas to liquid?

ΔH = - & ΔS = - Signup and view all the answers

What is the classification of phase change from gas to solid?

ΔH = - & ΔS = - Signup and view all the answers

Which of the reactions are spontaneous (favorable)?

2Mg(s) + O2(g) ⟶ 2MgO(s), ΔG = -1137 kJ/mol Signup and view all the answers

When ΔG = 0,...

the reaction is at equilibrium. Signup and view all the answers

What is the reaction trend for 2A(g) + 2B(g) ⇌ 3C(g) with ∆H° = 254 kJ?

reactant-favored Signup and view all the answers

What is the reaction trend for A(s) + B(g) ⇌ 2C(g) with ∆H° = -109 kJ?

product-favored Signup and view all the answers

What is the reaction trend for 2A(g) + B(g) ⇌ 4C(g) with ∆H° = 322 kJ?

insufficient information Signup and view all the answers

What is the reaction trend for A(g) + 2B(g) ⇌ 2C(g) with ∆H° = -89?

insufficient information Signup and view all the answers

What is the boiling point of dichloromethane given ΔHvap of 28.06 kJmol−1 and ΔSvap of 89.65 Jmol−1 *K−1?

39.84°C Signup and view all the answers

Calculate ΔG for a reaction at 298 K if ΔH = 139.99 kJ/mol and ΔS = 298.7 J/(mol·K). What can be said about the spontaneity?

ΔG = 50.98 kJ/mol, nonspontaneous Signup and view all the answers

For the statement ‘Spontaneous as written at all temperatures’, what are the values for ΔH and ΔS?

ΔH = -, ΔS = + Signup and view all the answers

For the statement ‘Spontaneous in reverse at all temperatures’, what are the values for ΔH and ΔS?

ΔH = +, ΔS = - Signup and view all the answers

For the statement ‘Spontaneous as written above a certain temperature’, what are the values for ΔH and ΔS?

ΔH = +, ΔS = + Signup and view all the answers

For the statement ‘Spontaneous as written below a certain temperature’, what are the values for ΔH and ΔS?

ΔH = -, ΔS = - Signup and view all the answers

What happens to entropy when ∆n gas = 1?

increases Signup and view all the answers

What happens to entropy when ∆n gas = 0?

has little or no change Signup and view all the answers

What happens to entropy when ∆n gas = -1?

decreases Signup and view all the answers

Which process is necessarily driven by an increase in the entropy of the surroundings?

The freezing of water Signup and view all the answers

Which law states ΔU = q + w?

1st Law of Thermodynamics Signup and view all the answers

Which law states ∆S univ > or = to 0?

2nd Law of Thermodynamics Signup and view all the answers

Which law states S = kB × ln(W)?

3rd Law of Thermodynamics Signup and view all the answers

Which law states the energy of the universe is constant and can neither be created nor destroyed?

1st Law of Thermodynamics Signup and view all the answers

Which law states for any reaction that occurs, then the entropy of the universe must increase?

2nd Law of Thermodynamics Signup and view all the answers

Which law states the entropy of a perfect crystal at absolute zero is 0?

3rd Law of Thermodynamics Signup and view all the answers

What is the melting point of silver given ΔHfus of 11.30 kJ⋅mol−1 and ΔSfus of 9.150 J⋅mol−1⋅K−1?

961.82°C Signup and view all the answers

When ΔG < 0, the reaction is ________ in the forward direction.

spontaneous Signup and view all the answers

If a reaction has a standard free-energy change of −18.70 kJ/mol, calculate the equilibrium constant at 25 °C.

Keq = 1888.35 Signup and view all the answers

If ΔG° < 0, then K < or ______.

<blockquote> 1 </blockquote> Signup and view all the answers

If ΔG° = 0, then K ____ 1.

= Signup and view all the answers

If ΔG° > 0, then K < or > 1.

< 1 Signup and view all the answers

Complete the statement. ΔG = ΔG° when _____.

Q = 1 Signup and view all the answers

For the reaction C2H6(g) + H2(g) ⇌ 2CH4(g) with ΔG° = −69.0 kJ/mol, calculate ΔG at 298 K when partial pressures are given.

ΔG = -63.85 kJ/mol Signup and view all the answers

Only ΔG ___ 0 is true at equilibrium.

= Signup and view all the answers

Study Notes

Chemical Thermodynamics

Focuses on heat and work in chemical reactions and physical changes.
Spontaneous processes occur under specific conditions, with ΔS univ > 0.
Non-spontaneous processes do not proceed under specified conditions.

Laws of Thermodynamics

1st Law: Energy of the universe is constant; energy can only be transferred, not created or destroyed.
2nd Law: Spontaneous processes lead to an increase in entropy; represented by S = k*ln(w) where k = 1.38 x 10⁻²³ J/K.
3rd Law: Entropy of a perfect crystalline substance at absolute zero (0 K) is zero.

Entropy (S)

Measures disorder or randomness in a system; reflects energy distribution.
Higher temperatures increase kinetic energy, leading to increased entropy as particles move faster.

Microstates and Macrostates

Microstates: Different energetically equivalent arrangements of particles in a system.
Macrostates: Set of microstates that results in the same energy level.

Equations

Change in reaction entropy: ∆S° rxn = Σm[S°(products)] - Σn[S°(reactants)].
Change in universal entropy: ∆S univ = ∆S sys + ∆S surr.
In isothermal processes, entropy change of surroundings is ∆S surr = -q sys / T.

Gibb's Free Energy (G)

Determines spontaneity of processes: G = H - TS.
At equilibrium, ΔG = 0; ΔG < 0 indicates spontaneity.

Spontaneity Conditions

Spontaneous at all temperatures if ΔH < 0 and ΔS > 0.
Non-spontaneous at all temperatures if ΔH > 0 and ΔS < 0.
Mixture of responses depending on temperature excess in other scenarios.

Entropy Changes in Phase Transitions

Changes from solid to liquid (ΔH = +, ΔS = +) and other phase changes often result in increased entropy.
Release of heat energy changes the kinetic energy of surroundings; higher temperatures reduce entropy change impact.

Evaluating Reactions

A negative ΔG implies a spontaneous reaction, while a zero ΔG suggests equilibrium.
Specific entropy changes denote the system's behavior like gas transitions affecting entropy.

Equilibrium Constants and ΔG

If ΔG° < 0, then K > 1 indicating product-favored reactions.
If ΔG° > 0, then K < 1 indicating reactant-favored reactions.

Specific Calculations

Boiling point of dichloromethane calculated, indicating equilibrium at ΔG = 0.
Changes in free energy at non-standard conditions using partial pressures are calculable via ΔG = ΔG° + RTln(Q).

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Test your understanding of Chemical Thermodynamics in this quiz covering spontaneous and non-spontaneous processes. Delve into essential definitions and concepts crucial for mastering the subject. Perfect for exam preparation and reinforcing key principles.

Chem 175 - Chapter 18 Chemical Thermodynamics

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Questions and Answers

What is Chemical Thermodynamics?

What are Spontaneous Processes?

What are Non-spontaneous Processes?

What is the 1st Law of Thermodynamics?

What is the 2nd Law of Thermodynamics?

What is Entropy (S)?

An increase in temperature increases the KE, which ________ the entropy.

What are Microstates?

What is a Macrostate?

What is the 3rd Law of Thermodynamics?

What is the equation for ∆S° rxn?

What is the equation for ∆S univ?

What are Isothermal Processes?

The effect of entropy change of the system on entropy of surroundings is smaller at _________ temps than _______ temps.

At __________ temps, surroundings have higher KE and the release of heat energy by the system will increase that KE by a lower % than at _______ temps.

In an exothermic reaction, the q sys ___ 0.

What is Gibb's Free Energy, G?

What is Standard Free Energies of Formation, ∆Gf°?

When ∆H < 0, ∆S > 0, and -T∆S < 0, the reaction is _______________.

When ∆H > 0, ∆S < 0, and -T∆S > 0, the reaction is _______________.

When ∆H < 0, ∆S < 0, and -T∆S > 0, the reaction is _______________.

When ∆H > 0, ∆S > 0, and -T∆S < 0, the reaction is _______________.

∆S is positive when the distribution becomes more or less equally distributed.

Arrange the compounds from highest to lowest standard molar entropy, Sº:

How is the entropy of Ar affected when it changes from liquid to gas?

How is the entropy of Cu affected when it changes from 300K to 800K?

How is the entropy of Fe affected when it changes from 250K to 25K?

What statement about the spontaneity and rate of a reaction is true?

Which process is necessarily driven by an increase in the entropy of the surroundings?

Is a cup of hot coffee cooling to room temperature spontaneous or nonspontaneous?

Is iron rusting in moist air spontaneous or nonspontaneous?

Is water being separated into H2 and O2 gas at 25°C spontaneous or nonspontaneous?

Is iron metal being extracted from iron ore spontaneous or nonspontaneous?

Is perfume molecules spreading out to fill the entire room spontaneous or nonspontaneous?

What is the classification of phase change from solid to liquid?

What is the classification of phase change from liquid to gas?

What is the classification of phase change from solid to gas?

What is the classification of phase change from liquid to solid?

What is the classification of phase change from gas to liquid?

What is the classification of phase change from gas to solid?

Which of the reactions are spontaneous (favorable)?

When ΔG = 0,...

What is the reaction trend for 2A(g) + 2B(g) ⇌ 3C(g) with ∆H° = 254 kJ?

What is the reaction trend for A(s) + B(g) ⇌ 2C(g) with ∆H° = -109 kJ?

What is the reaction trend for 2A(g) + B(g) ⇌ 4C(g) with ∆H° = 322 kJ?

What is the reaction trend for A(g) + 2B(g) ⇌ 2C(g) with ∆H° = -89?

What is the boiling point of dichloromethane given ΔHvap of 28.06 kJmol−1 and ΔSvap of 89.65 Jmol−1 *K−1?

Calculate ΔG for a reaction at 298 K if ΔH = 139.99 kJ/mol and ΔS = 298.7 J/(mol·K). What can be said about the spontaneity?

For the statement ‘Spontaneous as written at all temperatures’, what are the values for ΔH and ΔS?

For the statement ‘Spontaneous in reverse at all temperatures’, what are the values for ΔH and ΔS?

For the statement ‘Spontaneous as written above a certain temperature’, what are the values for ΔH and ΔS?

For the statement ‘Spontaneous as written below a certain temperature’, what are the values for ΔH and ΔS?

What happens to entropy when ∆n gas = 1?

What happens to entropy when ∆n gas = 0?

What happens to entropy when ∆n gas = -1?

Which process is necessarily driven by an increase in the entropy of the surroundings?

Which law states ΔU = q + w?

Which law states ∆S univ > or = to 0?

Which law states S = kB × ln(W)?

Which law states the energy of the universe is constant and can neither be created nor destroyed?

Which law states for any reaction that occurs, then the entropy of the universe must increase?

Which law states the entropy of a perfect crystal at absolute zero is 0?

What is the melting point of silver given ΔHfus of 11.30 kJ⋅mol−1 and ΔSfus of 9.150 J⋅mol−1⋅K−1?

When ΔG < 0, the reaction is ________ in the forward direction.

If a reaction has a standard free-energy change of −18.70 kJ/mol, calculate the equilibrium constant at 25 °C.

If ΔG° < 0, then K < or ______.

If ΔG° = 0, then K ____ 1.

If ΔG° > 0, then K < or > 1.

Complete the statement. ΔG = ΔG° when _____.

For the reaction C2H6(g) + H2(g) ⇌ 2CH4(g) with ΔG° = −69.0 kJ/mol, calculate ΔG at 298 K when partial pressures are given.

Only ΔG ___ 0 is true at equilibrium.

Study Notes

Chemical Thermodynamics

Laws of Thermodynamics

Entropy (S)

Microstates and Macrostates

The effect of entropy change of the system on entropy of surroundings is smaller at ___ temps than _ temps.

At ____ temps, surroundings have higher KE and the release of heat energy by the system will increase that KE by a lower % than at _ temps.