Thermodynamics: Reaction Enthalpy Calculation
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Questions and Answers

What is the standard molar formation enthalpy of a substance?

  • The enthalpy change for the reaction in which a substance is decomposed into its constituent elements.
  • The enthalpy change for the reaction in which a substance is formed from its constituent elements in their standard states. (correct)
  • The enthalpy change for the reaction in which a substance is formed from its constituent elements in any state.
  • The enthalpy change for the reaction in which a substance is completely burned in oxygen.

What is the purpose of using standard molar formation enthalpy and standard molar combustion enthalpy?

  • To calculate the standard molar reaction enthalpy. (correct)
  • To calculate the internal energy.
  • To calculate the absolute enthalpy.
  • To calculate the heat capacity.

What is the condition for calculating the standard molar reaction enthalpy?

  • The reaction conditions do not matter.
  • The reaction conditions must be identical. (correct)
  • The reaction conditions must be standard.
  • The reaction conditions must be different.

What is the unit of standard molar enthalpy?

<p>kJ/mol (C)</p> Signup and view all the answers

What is the difference between standard molar formation enthalpy and standard molar combustion enthalpy?

<p>Formation enthalpy is for reaction with elements, combustion enthalpy is for reaction with oxygen. (C)</p> Signup and view all the answers

What is the formula to calculate the standard molar reaction enthalpy?

<p>ΔrHmθ = ΣiΔfHm,iθ - ΣjΔfHm,jθ (D)</p> Signup and view all the answers

What is the formula to calculate the standard molar combustion enthalpy?

<p>ΔcHmθ = ΔH1 - ΔH2 (D)</p> Signup and view all the answers

Why is the standard molar combustion enthalpy used?

<p>Because most organic compounds cannot be directly synthesized from their constituent elements. (C)</p> Signup and view all the answers

What is the relationship between the standard molar reaction enthalpy and the standard molar formation enthalpy?

<p>ΔrHmθ = ΣiΔfHm,iθ - ΣjΔfHm,jθ (D)</p> Signup and view all the answers

What is the unit of ΔrHmθ?

<p>kJ/mol (C)</p> Signup and view all the answers

What is the standard state of a substance?

<p>The state at a standard temperature and pressure (C)</p> Signup and view all the answers

What is the definition of standard enthalpy change?

<p>The change in enthalpy at constant temperature and pressure (C)</p> Signup and view all the answers

What is the unit of standard enthalpy change?

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

What is the relationship between ΔH and ΔcH?

<p>ΔH = ΔcH (A)</p> Signup and view all the answers

What is the purpose of Hess's law?

<p>To calculate the enthalpy change of a reaction (B)</p> Signup and view all the answers

What is the definition of bond enthalpy?

<p>The energy required to break a bond (C)</p> Signup and view all the answers

What is the difference between ΔH and ΔU?

<p>ΔH is the change in enthalpy, while ΔU is the change in internal energy (A)</p> Signup and view all the answers

What is the purpose of Kirchhoff's equation?

<p>To calculate the enthalpy change of a reaction at different temperatures (B)</p> Signup and view all the answers

What is the definition of heat capacity?

<p>The amount of heat required to raise the temperature of a substance by 1°C (A)</p> Signup and view all the answers

What is the relationship between Cp and Cv?

<p>Cp = Cv + R (C)</p> Signup and view all the answers

Flashcards

Standard Molar Formation Enthalpy

The enthalpy change for the reaction in which a substance is formed from its constituent elements in their standard states.

Standard Molar Combustion Enthalpy

The enthalpy change for the reaction in which one mole of a substance is completely burned in excess oxygen under standard conditions.

Standard Molar Reaction Enthalpy

The enthalpy change for a reaction carried out under standard conditions.

Unit of Standard Molar Enthalpy

kJ/mol

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Formula for Standard Molar Reaction Enthalpy

The sum of the standard molar formation enthalpies of the products minus the sum of the standard molar formation enthalpies of the reactants.

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Standard State

A state of a substance at a defined standard temperature and pressure.

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Standard Enthalpy Change

The change in enthalpy that occurs when a process is carried out at constant temperature and pressure.

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Unit of Standard Enthalpy Change

kJ/mol

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Hess's Law

A law used to calculate the enthalpy change of a reaction by adding or subtracting the enthalpy changes of a series of known reactions.

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Bond Enthalpy

The energy required to break one mole of a specific bond in a gaseous molecule.

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Change in Internal Energy (ΔU)

The change in internal energy of a system during a process.

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Kirchhoff's Equation

An equation used to calculate the enthalpy change of a reaction at different temperatures.

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Molar Heat Capacity

The amount of heat required to raise the temperature of one mole of a substance by one degree Celsius.

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Heat Capacity at Constant Pressure (Cp)

The heat capacity of a substance at constant pressure.

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Heat Capacity at Constant Volume (Cv)

The heat capacity of a substance at constant volume.

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Relationship between Cp and Cv

The difference between the heat capacities at constant pressure and constant volume.

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Why Standard Molar Combustion Enthalpy is Used

Standard molar enthalpy of combustion is a measure of the heat released when 1 mole of a substance is completely burned in oxygen under standard conditions. It is useful because most organic compounds cannot be directly synthesized from their constituent elements, so their standard molar formation enthalpy is not available.

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Relationship Between Standard Molar Reaction Enthalpy and Standard Molar Formation Enthalpy

The relationship between the standard molar reaction enthalpy and the standard molar formation enthalpy of the reactants and products, as given by the formula ΔrHmθ = ΣiΔfHm,iθ - ΣjΔfHm,jθ.

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Unit of ΔrHmθ

kJ/mol

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Formula for Standard Molar Combustion Enthalpy

ΔrHmθ = ΣiΔfHm,iθ - ΣjΔfHm,jθ

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