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What is thermochemistry the study of?
What is thermochemistry the study of?
Thermochemistry is the study of the energy transferred as heat during the course of chemical reactions.
An exothermic process releases heat and has a negative enthalpy change.
An exothermic process releases heat and has a negative enthalpy change.
True (A)
An endothermic process absorbs heat and has a positive enthalpy change.
An endothermic process absorbs heat and has a positive enthalpy change.
True (A)
What is the standard state of a substance at a specified temperature?
What is the standard state of a substance at a specified temperature?
What is the standard enthalpy change, represented by ΔΗ°?
What is the standard enthalpy change, represented by ΔΗ°?
The standard enthalpy change for a reaction (or a physical process) at a specified temperature can be calculated using the equation: ______ = H° (Products) - H° (Reactants).
The standard enthalpy change for a reaction (or a physical process) at a specified temperature can be calculated using the equation: ______ = H° (Products) - H° (Reactants).
What is the standard enthalpy of vaporization, represented by AvapH°?
What is the standard enthalpy of vaporization, represented by AvapH°?
What is the standard enthalpy change that accompanies a change of physical state called?
What is the standard enthalpy change that accompanies a change of physical state called?
What is the standard enthalpy of transition denoted by?
What is the standard enthalpy of transition denoted by?
H is a ______ function, meaning that ∆H is independent of the path between the two states.
H is a ______ function, meaning that ∆H is independent of the path between the two states.
What is the lattice enthalpy, denoted by ΔΗL, the change in?
What is the lattice enthalpy, denoted by ΔΗL, the change in?
How are experimental values of AH₁ obtained?
How are experimental values of AH₁ obtained?
The Born-Haber cycle is a closed path of transformations that start and ends at the same point.
The Born-Haber cycle is a closed path of transformations that start and ends at the same point.
At normal temperatures, ΔΗL and AU differ by only a few kilojoules per mole, and the difference is typically neglected.
At normal temperatures, ΔΗL and AU differ by only a few kilojoules per mole, and the difference is typically neglected.
What are the two ways to report a change in enthalpy that accompanies a chemical reaction?
What are the two ways to report a change in enthalpy that accompanies a chemical reaction?
Why is Hm multiplied by its stoichiometric coefficient?
Why is Hm multiplied by its stoichiometric coefficient?
Hess's law states that the standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which a reaction may be divided.
Hess's law states that the standard enthalpy of an overall reaction is the sum of the standard enthalpies of the individual reactions into which a reaction may be divided.
The standard enthalpy of formation, ΔΗf°, of a substance is the standard reaction enthalpy for the formation of the compound from its elements in their reference states.
The standard enthalpy of formation, ΔΗf°, of a substance is the standard reaction enthalpy for the formation of the compound from its elements in their reference states.
Enthalpies of formation are zero for elements in their reference states, but non-zero for compounds, even at standard conditions.
Enthalpies of formation are zero for elements in their reference states, but non-zero for compounds, even at standard conditions.
The temperature dependence of reaction enthalpies can be calculated using Kirchhoff's law.
The temperature dependence of reaction enthalpies can be calculated using Kirchhoff's law.
Flashcards
Thermochemistry
Thermochemistry
The study of energy changes that occur during chemical reactions, particularly the heat transferred.
Exothermic process
Exothermic process
A chemical reaction that releases heat into the surroundings.
Endothermic process
Endothermic process
A chemical reaction that absorbs heat from the surroundings.
Standard enthalpy change (ΔH°)
Standard enthalpy change (ΔH°)
The enthalpy change for a reaction when all reactants and products are in their standard states.
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Standard state
Standard state
The pure form of a substance at 1 bar pressure and a specified temperature.
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Standard enthalpy of vaporization (ΔvapH°)
Standard enthalpy of vaporization (ΔvapH°)
The enthalpy change when a liquid changes into a gas at 1 bar pressure.
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Standard enthalpy of fusion (ΔfusH°)
Standard enthalpy of fusion (ΔfusH°)
The enthalpy change when a solid changes into a liquid at 1 bar pressure.
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Standard enthalpy of transition (ΔtrsH°)
Standard enthalpy of transition (ΔtrsH°)
The enthalpy change that accompanies a change of physical state.
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Standard enthalpy of sublimation (ΔsubH°)
Standard enthalpy of sublimation (ΔsubH°)
The enthalpy change when a solid changes directly into a gas at 1 bar pressure.
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State function (H)
State function (H)
A state function is a property that depends only on the initial and final states, not the path taken to get there.
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Lattice enthalpy (ΔHL)
Lattice enthalpy (ΔHL)
The enthalpy change associated with breaking a solid ionic compound into its gaseous ions.
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Born-Haber cycle
Born-Haber cycle
A diagram used to calculate the lattice enthalpy of an ionic compound.
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Standard reaction enthalpy (ΔrH°)
Standard reaction enthalpy (ΔrH°)
The enthalpy change per mole of reaction when all reactants and products are in their standard states.
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Standard enthalpy of formation (ΔfH°)
Standard enthalpy of formation (ΔfH°)
The enthalpy change for the formation of 1 mole of a compound from its elements in their standard states.
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Hess's law
Hess's law
Hess's law states that the total enthalpy change of a reaction is independent of the path taken, only depending on the initial and final states.
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Hess's law
Hess's law
A law that indicates that the enthalpy change of a reaction can be determined by combining the enthalpy changes of other individual reactions.
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Reaction enthalpy in terms of enthalpies of formation
Reaction enthalpy in terms of enthalpies of formation
The change in enthalpy of a reaction can be calculated using the standard enthalpies of formation of the reactants and products.
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Kirchhoff's law
Kirchhoff's law
A law that relates the standard enthalpy change of a reaction at two different temperatures.
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Kirchhoff's law
Kirchhoff's law
A law that describes the temperature dependence of enthalpy changes.
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Halogens
Halogens
A group of six chemical elements in Group 17 (VIIA) of the periodic table.
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Halogen
Halogen
A non-metallic element found in Group 17 of the periodic table.
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Chlorine (Cl2)
Chlorine (Cl2)
A halogen that is yellowish-green in color, gaseous at room temperature, and used in many industrial and household applications.
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Laboratory preparation of chlorine
Laboratory preparation of chlorine
A method of preparing chlorine gas in a laboratory setting.
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Reaction of Chlorine with bases
Reaction of Chlorine with bases
A chemical reaction in which chlorine reacts with a hot solution of sodium hydroxide.
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Reaction of chlorine with water
Reaction of chlorine with water
A chemical reaction in which chlorine reacts with water, producing hydrochloric acid and hypochlorous acid.
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Oxidizing reaction of chlorine
Oxidizing reaction of chlorine
A chemical reaction in which chlorine acts as an oxidizing agent, increasing the oxidation state of a substance.
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Halogenation of organic compounds
Halogenation of organic compounds
A chemical process that involves the replacement of one or more hydrogen atoms in an organic compound with a halogen atom.
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Displacement reaction of halogens
Displacement reaction of halogens
A reaction where a halogen displaces a less electronegative halogen from a compound.
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Common oxidation states of chlorine
Common oxidation states of chlorine
The common oxidation states of chlorine are -1 and 0.
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Reaction of chlorine with air
Reaction of chlorine with air
The reaction of chlorine with air, where chlorine does not react readily with oxygen or nitrogen.
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Thermochemistry
- Thermochemistry is the study of energy transfer as heat during chemical reactions.
- Energy absorbed is positive, energy released is negative
- Exothermic process - a chemical reaction that releases heat into its surroundings, ∆H < 0
- Endothermic process - a chemical reaction that absorbs heat from its surroundings, ∆H > 0
Standard Enthalpy Changes
- Standard enthalpy change (∆H°) - a change in enthalpy for a reaction where the initial and final substances are in their standard states.
- Standard state - of a substance is its pure form at 1 bar.
- Example: Liquid ethanol at 298 K is pure liquid ethanol at 298 K and 1 bar.
- ∆rH° = ∆rH°(products) - ∆rH°(reactants)
Standard Enthalpy of Vaporization
-
The standard enthalpy of vaporization (∆vapH°) is the enthalpy change per mole when a pure liquid at atmospheric pressure vaporizes to a gas at the same pressure
- ∆vapH°(373 K) = +40.66 kJ mol⁻¹
Enthalpies of Physical Change
- The standard enthalpy change that accompanies a change of physical state is called the standard enthalpy of transition and is denoted ∆trsH°
- Standard enthalpy of fusion, ∆fusH°, is the enthalpy change when 1 mol of a solid substance melts to its liquid form at its melting point
- Standard enthalpy of vaporization, ∆vapH°, is the enthalpy change when 1 mol of a liquid substance vaporizes to its gaseous form at its boiling point
Hess's Law
- Hess's Law states that the enthalpy change for an overall reaction is the sum of the enthalpy changes for the individual reactions into which the reaction can be divided.
- The standard enthalpy change for a reaction is independent of the reaction pathway.
Standard Enthalpies of Formation
- The standard enthalpy of formation (∆fH°) of a substance is the standard reaction enthalpy for the formation of the compound from its elements in their most stable states (reference states) at a certain temperature and pressure
Temperature Dependence of Reaction Enthalpies
- Kirchhoff's Law - states that the standard enthalpy of reaction is dependent on temperature.
- ∆rH°(T₂) = ∆rH°(T₁) + (T₂ – T₁) ∆rCp where ∆rCp is the change in heat capacity for the reaction
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