Unit 13b: Thermodynamics II: Reaction Thermochemistry
Reading
BJU book: Read Ch. 13 "Chemical Thermodynamics" from Enthalpy of Reaction to the end of the chapter
Topics
Labs
Thermite lab
BJU book: Read Ch. 13 "Chemical Thermodynamics" from Enthalpy of Reaction to the end of the chapter
Topics
- Heat (enthalpy) of reaction
- Heat of formation
- Heat of combustion
- Entropy and Free-Energy as a predictor of reaction tendency
Labs
Thermite lab
Below: Fire Breathing Pumpkin. This illustrates the famous "Thermite" reaction. Thermite is a mixture of finely-ground aluminum powder and red iron oxide, which is thoroughly mixed and ignited with a white-hot magnesium fuse. It is highly exothermic and burns at around 3,000 F, enough to melt solid iron. In fact, it is used to field-weld steel railroad rails.
Lecture outline
In the previous unit we were discussing the heating and cooling of simple substances. Melting ice into water and then boiling the water into steam was a good example.
In this unit, we are discussing the energy involved in chemical reactions. A good example is combining oxygen and hydrogen gases to form water and produce energy in a fuel cell. More dramatic examples are the Thermite and black powder reactions. An example from biochemistry is your body converting glucose (blood sugar) into energy.
Topics
In the previous unit we were discussing the heating and cooling of simple substances. Melting ice into water and then boiling the water into steam was a good example.
In this unit, we are discussing the energy involved in chemical reactions. A good example is combining oxygen and hydrogen gases to form water and produce energy in a fuel cell. More dramatic examples are the Thermite and black powder reactions. An example from biochemistry is your body converting glucose (blood sugar) into energy.
Topics
- Reaction energy diagrams
- Enthalpy of reaction, formation, and combustion. Hess' Law.
- Entropy and 2nd Law of Thermodynamics. Reaction tendency.
- Gibbs Free Energy. Calculating changes in free energy.
Thermite lab
We will (carefully) perform a Thermite demonstration using red iron oxide and aluminum powder.
The Thermite lab is an excellent launching pad for discussing:
We will (carefully) perform a Thermite demonstration using red iron oxide and aluminum powder.
The Thermite lab is an excellent launching pad for discussing:
- Stoichiometry: What is the correct ratio of reactants to use?
- Enthalpy of reaction: What makes the reaction go forward?
- Reactivity of metals: Aluminum vs. Iron
- Activation energy: Why do we need a magnesium fuse?
- Melting points of various metals: We will place other metals in the reactor and watch what happens to them.
"Concentration" PhET WebLab
| phet_-_concentration_weblab__revised_2020_.docx |
Calculating Enthalpy & Gibbs for the Thermite, Black Powder, and Fuel Cell reactions"
Watch the homework video below, but enter your actual work directly into Canvas. The questions are in Canvas.
Accompanying video is posted below:
Correction: at 27:45 delta-H has a "negative" value, as in -4,000 KJ
Correction: at 28:35 because of the above, delta-G also has a "negative" value. Hint: it's between -4,000 and -4,500 KJ
Accompanying video is posted below:
Correction: at 27:45 delta-H has a "negative" value, as in -4,000 KJ
Correction: at 28:35 because of the above, delta-G also has a "negative" value. Hint: it's between -4,000 and -4,500 KJ