Each pre-class Podia question is based on the pre-class material and working through the pre-class material will help you formulate your response. Consider the problem and write down/draw out your solution in your class notebook. These questions are designed to hone your skills so that you can analyze and solve mastery problems you will encounter throughout the course.
Two days before the next whole-class session, the pre-class Podia question will become visible in Podia, where you can click on the prompt and submit your answer.
Submissions for pre-class Podia activities are due 1 hour before the start of your whole-class. Be sure to submit your response before the due time.
Day 20 Pre-Class Podia Activity
Earth’s original atmosphere did not contain large amounts of oxygen. The action of UV radiation on water molecules, combined with the production of oxygen by photosynthetic organisms dramatically increased the proportion of O2(g) in the atmosphere. Oxygen gas reacted with different metals on Earth’s surface to produce a variety of ionic compounds, as in the following processes:
| chemical process | ΔrxnH (kJ/mol) |
| 2 Fe(s) + 3/2 O2(g) → Fe2O3(s) | –824 |
| Ti(s) + O2(g) → TiO2(s) | –944 |
| Ca(s) + ½ O2(g) → CaO(s) | –635 |
| Ba(s) + ½ O2(g) → BaO(s) | –548 |
Use your understanding of ionic compounds to explain the observed differences in the enthalpies of reactions for these processes. Discuss why some of these processes may be more energetically favored than others.
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