Bond Enthalpy Calculation 25
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Questions and Answers

Free Energy (G) has two components, Enthalpy (H) and Entropy (S)?

True

The Law of Conservation of Energy states that energy can be created but not destroyed?

False

Changes in entropy deal with changes in chemical bonding or non-covalent interactions?

False

Energy comes in two main types: Kinetic energy and Mechanical energy?

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

Enthalpy has a larger contribution to free energy at high temperatures?

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

Hess’ Law deals with changes in equilibrium and Gibbs Free Energy?

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

Energy can be created and destroyed according to the law of thermodynamics.

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

The surroundings in a thermodynamic system refer to the vessel of interest where reactions take place.

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

An open system can exchange both energy and matter with its surroundings.

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

Adiabatic barriers allow for efficient energy transfer between the system and surroundings.

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

If A is in thermal equilibrium with B, and B is in thermal equilibrium with C, then A will also be in thermal equilibrium with C according to the Zeroth Law of Thermodynamics.

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

Work is required to push air from the lungs against atmospheric pressure.

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

A system does the most work possible when the opposing pressure is greater than the internal pressure.

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

The heat capacity of a substance can be used to obtain the quantity of transferred heat via q = CΔT.

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

For reversible isothermal expansion of a perfect gas, the internal energy ΔU is equal to zero.

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

The internal energy of a system refers to the total energy (kinetic + potential) of all the atoms, molecules, and ions constituting the system.

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

The first law of thermodynamics states that isolated systems can do work upon or heat their surroundings.

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

For any system that does work, new sources of energy must be supplied at regular intervals.

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

Enthalpy equals the change in internal energy plus the product of pressure and change in volume.

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

For an open system with external pressure pex, the change in enthalpy equals the heat transferred at constant pressure.

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

An exothermic process involves energy leaving the system as heat and has a positive change in enthalpy.

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

The heat capacity at constant pressure, Cp, is equal to the change in enthalpy divided by the change in temperature.

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

The standard molar enthalpy of a substance is denoted by Hmo and represents its enthalpy at 25°C and exactly 1 bar pressure.

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

The vaporization enthalpy of water is responsible for the high humidity of our climate and the presence of oceans.

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

Sublimation is the direct conversion of a solid to a liquid.

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

Differential Scanning Calorimetry measures the difference in heat transferred to or from a sample in comparison to a reference material.

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

The overall enthalpy change of a process is equal to the sum of the sublimation and vaporization enthalpies.

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

Breaking bonds (dissociation) are always exothermic processes.

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

Entropy is the measure of how concentrated energy and matter is.

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

The entropy of an isolated system tends to decrease.

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

The change in entropy of a substance is equal to the heat transferred reversibly to it divided by the temperature at which the transfer takes place.

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

Entropy is not a state function.

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

When increasing the number of energy packets over 80 atoms, the probability of the hot bar getting hotter increases.

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

The resulting change in entropy when transferring 100 kJ of heat to a large body of water at 0 °C is +366 J K-1.

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

Melting or boiling results in a decrease in entropy.

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

The entropy of vaporization of water at 25 °C is -118 J K-1 mol-1.

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

Humans, even at rest, do not constantly expend energy.

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

At absolute zero, the absolute entropies of all perfectly crystalline substances are zero.

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

Standard molar entropies can be obtained by following the changes in heat capacity of a given substance with temperature.

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

Entropy can be negative for a substance at a certain temperature.

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

Hydrogen peroxide is formed in the body due to reactions involving oxygen.

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

The enthalpy change for the reaction 2H2O2(l) ➞ 2H2O(l) + O2(g) is -172 kJ.

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

Standard enthalpy of combustion for CH4(g) is -890 kJ mol-1.

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

Fats are used for energy storage in mammals and to provide insulation.

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

Proteins are usually used to create new proteins instead of being employed as a fuel source.

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

The standard enthalpy of a reaction is the sum of the standard enthalpies of the reactions into which the overall reaction may be divided.

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

During vigorous exercise, muscle cells become deprived of oxygen, leading to the production of lactic acid (LA).

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

Isothermal expansion of a perfect gas into a vacuum has no overall change in energy.

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

Gas molecules move randomly, and the probability that they will move into one corner of a container is significant.

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

Spontaneous processes necessarily move in the direction of lower energy.

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

Gases expand to fill empty spaces, which is a non-spontaneous process.

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

In a cooling process, the energy lost by the system is destroyed and cannot be transferred to the surroundings.

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

The standard reaction entropy, ΔrS∅, is the difference in molar entropy between the products and reactants of a reaction in their standard states?

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

The standard reaction entropy of an enzyme catalyzed reaction at 25 °C is +96.3 J K-1 mol-1?

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

Processes occur spontaneously if the overall entropy of the universe is decreased?

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

According to the 2nd Law of Thermodynamics, the entropy of an isolated system tends to decrease?

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

The Gibbs energy and Entropy have the same signs?

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

Josiah Willard Gibbs was the first person to receive a PhD in Engineering from Yale?

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

The ΔG of any process is the maximum expansion work that can be extracted from that process at constant temperature and pressure?

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

The change in Gibbs energy accompanying combustion of glucose at 25 °C is +2828 kJ mol-1?

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

ATP hydrolysis drives favorable biochemical reactions?

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

The standard reaction Gibbs energy, ΔrGo, can be calculated using tabulated values obtained by combining standard enthalpies and entropies?

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

Which component of free energy has a higher contribution at higher temperatures?

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

What type of energy is associated with movement?

<p>Kinetic energy</p> Signup and view all the answers

In the equation G = H - TS, what does 'T' represent?

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

According to the text, what type of energy is possessed due to position?

<p>Potential energy</p> Signup and view all the answers

What does the equation ∆Gⱡ = ∆Hⱡ - T∆Sⱡ represent?

<p>Non-standard Gibbs free energy change</p> Signup and view all the answers

What deals with changes in order or disorder associated with a process?

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

What is the standard enthalpy of combustion for CH4(g)?

<p>-890 kJ mol-1</p> Signup and view all the answers

What type of process is the isothermal expansion of a perfect gas into a vacuum?

<p>Spontaneous process</p> Signup and view all the answers

Which statement about spontaneous processes is true?

<p>They always move in the direction of lower energy.</p> Signup and view all the answers

What is the standard enthalpy of formation of liquid water?

<p>-286 kJ mol-1</p> Signup and view all the answers

What drives favorable biochemical reactions?

<p>ATP hydrolysis</p> Signup and view all the answers

What happens during vigorous exercise when muscle cells become deprived of oxygen?

<p>Glucose cannot be completely oxidized and is broken down to lactic acid</p> Signup and view all the answers

What is the enthalpy change for glycolysis?

<p>-120 kJ</p> Signup and view all the answers

What is the energy input required per day for 18-20 year old males?

<p>~12 MJ</p> Signup and view all the answers

Which type of fuel provides 17 kJ g-1?

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

What do proteins do in mammals?

<p>Used to create new proteins instead of being employed as a fuel source</p> Signup and view all the answers

What happens to fats in mammals?

<p>Are used for energy storage</p> Signup and view all the answers

How does body temperature regulated?

<p>Radiation and perspiration</p> Signup and view all the answers

What is the standard reaction entropy, ΔrS∅, for the reaction catalyzed by carbonic anhydrase?

<p>-96.3 J K-1 mol-1</p> Signup and view all the answers

What does the change in Gibbs energy, ΔG, represent for any process?

<p>Non-expansion work</p> Signup and view all the answers

At pH = 7.0 and T = 37 °C, what is the standard enthalpy change, ΔrH, for ATP hydrolysis?

<p>-20 kJ mol-1</p> Signup and view all the answers

What is the relationship between Gibbs energy and entropy for spontaneous processes?

<p>They have opposite signs</p> Signup and view all the answers

What is the maximum nonexpansion work that can be extracted from a process at constant temperature and pressure?

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

What is the standard reaction Gibbs energy, ΔrGo, for the reaction catalyzed by carbonic anhydrase at 25 °C?

<p>-274.6 kJ mol-1</p> Signup and view all the answers

What drives unfavourable biochemical reactions by providing up to 31 kJ of energy in the form of non-expansion work?

<p>ATP hydrolysis</p> Signup and view all the answers

What is the relationship between Gibbs energy and spontaneity?

<p>-ΔG leads to spontaneous processes</p> Signup and view all the answers

At what temperature are the absolute entropies of all perfectly crystalline substances zero?

<p>+0 K</p> Signup and view all the answers

What happens to Gibbs energy and entropy for spontaneous processes?

<p>-ΔG and +ΔS</p> Signup and view all the answers

If a process has a change in Gibbs energy of -2828 kJ mol-1 at 25 °C, what type of work does it represent?

<p>Non-expansion work</p> Signup and view all the answers

What is the relationship between Gibbs energy and enthalpy for any process?

<p>They have opposite signs</p> Signup and view all the answers

What is the measure of how dispersed energy and matter is?

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

What is the change in entropy of a substance equal to?

<p>$q_{rev}/T$</p> Signup and view all the answers

What is the probability that we end up with 9 packets in the HOT bar, and 1 packet in the COLD bar?

<p>91520</p> Signup and view all the answers

What happens to the probability of the hot bar getting hotter as we increase the number of energy packets over 80 atoms?

<p>Drops drastically</p> Signup and view all the answers

What is the standard molar entropy, Sm∅, the measure of?

<p>Absolute entropies at absolute zero</p> Signup and view all the answers

In which scenario does entropy change, ΔS, increase?

<p>$ ext{Cp} imes ext{ln} (T_f/T_i)$ when $T_f &gt; T_i$</p> Signup and view all the answers

What does melting or boiling result in?

<p>Increase in entropy</p> Signup and view all the answers

What does the standard molar entropy, Sm∅, measure?

<p>$ ext{Sm}∅$ of perfectly crystalline substances at absolute zero</p> Signup and view all the answers

What does a person at rest constantly expend?

<p>$100 J s^{-1}$</p> Signup and view all the answers

What does the Third Law of Thermodynamics state?

<p>$ ext{S}(0) = 0$</p> Signup and view all the answers

"The amount of heat passing to / from the surroundings is equal and opposite to the heat leaving / entering the system". What does this statement imply?

<p>$ΔS_{sur} = -ΔH/T$</p> Signup and view all the answers

"Josiah Willard Gibbs was the first person to receive a PhD in Engineering from Yale?". Is this statement true?

<p>&quot;False&quot;</p> Signup and view all the answers

What is the fundamental principle of the conservation of energy?

<p>Energy is constant and cannot be created or destroyed</p> Signup and view all the answers

What is the system in thermodynamics?

<p>The vessel of interest where reactions take place</p> Signup and view all the answers

Which type of system can exchange energy but not matter with its surroundings?

<p>Closed system</p> Signup and view all the answers

What is the sign convention for work done on a system?

<p>Positive if work is done on the system</p> Signup and view all the answers

What is the formula for work associated with gas expansion?

<p>$w = -pexΔV$</p> Signup and view all the answers

What happens when work is required to push air from the lungs against atmospheric pressure?

<p>Negative work is done</p> Signup and view all the answers

What does the first law of thermodynamics state about the internal energy of a perfect gas during isothermal expansion?

<p>$ΔU = 0$</p> Signup and view all the answers

What is internal energy in thermodynamics?

<p>The total energy of all subatomic particles in a system</p> Signup and view all the answers

How can the quantity of heat transferred be obtained using heat capacity?

<p>$q = CΔT$</p> Signup and view all the answers

In thermodynamics, what does the first law state about isolated systems?

<p>Isolated systems can neither do work upon nor heat their surroundings.</p> Signup and view all the answers

What is the relationship between enthalpy change (ΔH) and heat transferred (q) for an exothermic process?

<p>ΔH = -q</p> Signup and view all the answers

What is responsible for the low humidity of the climate and the presence of oceans, according to the text?

<p>Vaporization enthalpy of water</p> Signup and view all the answers

What does sublimation refer to in thermodynamics?

<p>Direct conversion of a solid to a gas</p> Signup and view all the answers

What does differential scanning calorimetry measure?

<p>Difference in heat capacity of a substance with temperature</p> Signup and view all the answers

What represents the standard molar enthalpy of a substance?

<p>$H_m = U_m + RT$ at 25 °C</p> Signup and view all the answers

What is the standard reaction entropy (ΔrS∅) used to measure?

<p>Difference in molar entropy between products and reactants at standard conditions</p> Signup and view all the answers

What is responsible for the high vaporization enthalpy of water?

<p>Hydrogen bonding</p> Signup and view all the answers

What does the standard reaction Gibbs energy ($ ext{ΔrG∅}$) represent?

<p>$ ext{ΔrG∅}$ can be calculated using tabulated values obtained by combining standard enthalpies and entropies.</p> Signup and view all the answers

What does the standard molar enthalpy ($H^o_m$) represent?

<p>$H^o_m$ represents the enthalpy at 25 °C and exactly 1 bar pressure.</p> Signup and view all the answers

What contributes to the low humidity of our climate and presence of oceans?

<p>Vaporisation: ΔvapHo (H2O) = +44 kJ mol-1.</p> Signup and view all the answers

Which process involves energy entering the system as heat?

<p>Vaporisation: ΔvapHo (H2O) = +44 kJ mol-1.</p> Signup and view all the answers

Study Notes

Free Energy and Thermodynamics

  • Free Energy (G) is comprised of Enthalpy (H) and Entropy (S), represented as G = H - TS.
  • Enthalpy has a greater influence on free energy at elevated temperatures.
  • Gibbs Free Energy is the maximum work obtainable from a thermodynamic process at constant temperature and pressure.

Thermodynamic Laws and Systems

  • The Law of Conservation of Energy states that energy can neither be created nor destroyed, only transformed.
  • Open systems can interchange energy and matter with their surroundings, while closed systems can exchange only energy.
  • Adiabatic barriers facilitate efficient energy transfer between systems and surroundings.

Thermal Equilibrium and Pressure

  • Zeroth Law of Thermodynamics asserts that if A is in thermal equilibrium with B, and B with C, then A is in equilibrium with C.
  • Work is necessary to expel air from the lungs against atmospheric pressure.
  • A system accomplishes maximum work when external pressure exceeds internal pressure.

Internal Energy and Heat Transfer

  • Internal energy (ΔU) includes all kinetic and potential energy of particles within a system.
  • The relationship for heat transfer is defined by q = CΔT, where C is heat capacity.

Phase Changes and Enthalpy

  • Exothermic processes involve heat leaving the system, resulting in a positive change in enthalpy.
  • The standard molar enthalpy (Hmo) is measured at 25°C and 1 bar pressure.
  • Enthalpy changes during phase transitions (e.g., vaporization and sublimation) are significant in climate dynamics.

Entropy and Energy Distribution

  • Entropy measures energy and matter distribution, indicating the degree of disorder in a system.
  • The entropy of an isolated system generally tends to increase.
  • A change in entropy is calculated by the heat transferred reversibly divided by the temperature.

Spontaneous Processes

  • Processes occur spontaneously if they contribute to an overall increase in the entropy of the universe.
  • Spontaneous processes favor lower energy states and higher disorder.

Combustion and Biochemical Reactions

  • Standard enthalpy of combustion for methane (CH4) is -890 kJ mol-1.
  • Ideal enthalpy change for glycolysis and lactic acid buildup during oxygen deprivation in muscles.
  • ATP hydrolysis is a key process that drives many biochemical reactions by releasing energy.

Statistical Mechanics and Probability

  • As the number of energy packets increases, the likelihood of energy concentration changes, affecting temperature.
  • Melting or boiling transitions typically correspond with an increase in entropy.

Key Temperature Concepts

  • Absolute zero absolute entropy for perfectly crystalline substances is defined as zero entropy.
  • At specific conditions (pH = 7.0 and T = 37°C), standard enthalpy changes and reaction gibbs energies can be evaluated.

Fuel and Energy Utilization

  • Fats serve dual roles in energy storage and insulation in mammals, while proteins are primarily utilized for biosynthesis rather than as fuels.
  • Energy input for young males is significant, and different fuel types provide varying energy yields per gram.

Thermodynamic Relationships

  • The standard reaction entropy (ΔrS∅) represents the change in entropy from reactants to products in standard states.
  • Entropy can be a negative value under specific temperatures.
  • A negative change in Gibbs energy indicates a spontaneous process and can be interpreted as non-expansion work potential.

Summary of Formulas and Concepts

  • The general relationship between Gibbs energy and enthalpy for processes can be summarized as ΔG = ΔH - TΔS.
  • Standard reaction Gibbs energy can be derived from enthalpy and entropy values under standard conditions.

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Description

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