Mini-lecture: enthalpies of formation
Mini-lecture: Hess's Law
Mini-lecture: manipulating enthalpy and thermochemical expressions
Enthalpy and Thermochemical Expressions
Overview
This module covers four areas of enthalpy:
1- introduction to enthalpy and reaction-energy diagrams; define exothermic and endothermic
2- Thermochemical expressions and manipulating enthalpy
3- Hess's Law
4- Enthalpies of formation to find enthalpy of reaction
Introduction to enthalpy: Endothermic versus Exothermic
This mini-lecture defines enthalpy in an approachable way and defines exothermic and endothermic. Included is use of reaction-energy diagrams to identify exothermic or endothermic reactions.
Thermochemical Expressions
The video doesn't specify that dividing by a value will also result in the enthalpy being divided by that number.
This mini-lecture introduces thermochemical expressions and the concepts of 1- heat transfer is directional and 2- heat transfer is addittive.
This is a great primer for Hess's Law.
Hess's Law
Hess's Law is the evidence that the heat from chemical reactions is additive. If we had two reactions together to get a new reaction, we can get the enthalpy of the new reaction by adding the two reaction enthalpies.
This video is one of the longer ones since this concept is typically challenging for students.
Enthalpies of Formation
Students often need to recall standard states for individual elements when working on enthalpies of formation problems.
Another way to determine the overall enthalpy difference for a chemical reaction is using the enthalpies of formation for the reactants and products in your reaction.
In this mini-lecture, we define Hf as the enthalpy of formation, which means making one mole of a substance from its elements in their natural state. Then, we work an example using those values and a balanced reaction to find the enthalpy of the given balanced reaction.