Standard Enthalpies; From Brightspace Flashcards
What is the concept introduced in the lecture?
Standard enthalpy
What cycle is explained in relation to standard enthalpy?
Born-Haber cycle
List four examples of standard enthalpies presented.
- Enthalpy of Ionization
- Enthalpy of Electron Affinity
- Enthalpy of Formation
- Enthalpy of Combustion
What measurement is illustrated for determining the enthalpy of combustion?
Bomb calorimeter measurement
How can ∆H for a reaction be calculated?
From the tabulated ∆H values of other reactions
What does the enthalpy change, ∆H, depend on?
The amount of matter undergoing change and the nature of the initial and final states
True or False: Enthalpy change is independent of the number of steps in a reaction.
True
What does Hess’s law state?
∆H for the overall reaction equals the sum of the enthalpy changes for the individual steps
What is a consequence of enthalpy being a state function?
The overall enthalpy change is independent of the path taken
Why is Hess’s law useful?
It allows calculation of energy changes that are difficult to measure directly
What is the enthalpy of formation denoted as?
∆Hf
What does the subscript ‘f’ in ∆Hf indicate?
The substance has been formed from its constituent elements
What conditions define a standard state?
Pure form at atmospheric pressure (100 kPa) and 298 K
What is the standard enthalpy change denoted as?
∆H°
Fill in the blank: The enthalpy change associated with the formation of a compound from its elements is called the _______.
[enthalpy of formation]
What factors affect the magnitude of any enthalpy change?
- Temperature
- Pressure
- State (gas, liquid, or solid crystalline form)
What is an example of a reaction that is difficult to measure directly?
Combustion of carbon to form carbon monoxide
What can be used to calculate enthalpy changes for many reactions?
Tabulated ∆H values
What is the enthalpy of combustion?
∆H for combusting a substance in oxygen
Fill in the blank: The enthalpy change for converting liquids to gases is called the _______.
[enthalpy of vaporization]
Fill in the blank: The enthalpy change for melting solids is known as the _______.
[enthalpy of fusion]
