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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
An endothermic process absorbs heat and has a positive enthalpy change.
An endothermic process absorbs heat and has a positive enthalpy change.
True
What is the standard state of a substance at a specified temperature?
What is the standard state of a substance at a specified temperature?
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What is the standard enthalpy change, represented by ΔΗ°?
What is the standard enthalpy change, represented by ΔΗ°?
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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).
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What is the standard enthalpy of vaporization, represented by AvapH°?
What is the standard enthalpy of vaporization, represented by AvapH°?
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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?
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What is the standard enthalpy of transition denoted by?
What is the standard enthalpy of transition denoted by?
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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.
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What is the lattice enthalpy, denoted by ΔΗL, the change in?
What is the lattice enthalpy, denoted by ΔΗL, the change in?
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How are experimental values of AH₁ obtained?
How are experimental values of AH₁ obtained?
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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.
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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.
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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?
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Why is Hm multiplied by its stoichiometric coefficient?
Why is Hm multiplied by its stoichiometric coefficient?
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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.
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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.
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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.
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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.
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Study Notes
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
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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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Description
Explore the fundamentals of thermochemistry, focusing on energy transfer during chemical reactions. This quiz covers important concepts such as exothermic and endothermic processes, standard enthalpy changes, and the enthalpy of vaporization. Test your understanding of these critical topics in chemistry!
