Monday, January 10

Today we started class by grabbing our lab notebooks. We would need them for the lab that we would soon be doing. Next on our agenda, going over the webassign due today. It was a reading sheet, so we turned to page 27 (32) in our packets, and filled in the answers.

Answers:

1. C
2. B
3. C
4. C
5. B & C
6. False - The enthalpy value is relative to those values of other substances
7. B
8. A
9. To give off 185 kJ of heat
10. B
- B
- 370 kJ
- 1998 kJ
11. a. 6232.1 kJ
b. 91.0 kJ
12. D
13. B
14. D
15. 790 kJ
16. A
17. 40.64 kJ
18. (Delta)H4 = 40 kJ

Then it was time to learn about something new, Hess's law. We flipped to page 11 of our packet. Mr. H told us that this section of the unit would be one of the harder sections. But he also mentioned that it was a bit like algebra. 2 of my favorite things! Chemistry and algebra! But the way you would solve the problems went something like this.

1. Calculate (Delta)H for: 2C(s) + O2(g) --> 2CO2(g) (Delta)H = -393.5 kJ

Now to do this, we had to find a way to combine the formulas, like in algebra. In this situation, we multiplied all of the coefficients in the first formula by 2, and we flipped the second formula around making the (delta)H positive 566.

2C(s) + 2O2(g) --> 2CO2(g) (delta)H = -787 kJ
2CO2(g) --> 2CO(g) + O2(g) (delta)H = +566 kJ
and the result.
2C(s) + O2(g) --> 2CO2(g) (delta)H = -221kJ

2. Calculate (Delta)H for: 4Al(s) + 3MnO2(s) --> 2Al2O3(s) + 3Mn(s)

Now to solve this one we flipped the second formula and multiplied it by 3.

4Al(s) + 3O2(g) --> 2Al2O3(s) (delta)H = 3352 kJ
3MnO2(s) --> 3Mn(s) + 3O2(g) (delta)H = 1563 kJ
and the result.
4Al(s) + 3MnO2(s) --> 2Al2O3(s) + 3Mn(s) (delta)H = 4915 kJ

We finished the day with a lab. The lab was the "Heat of Formation Lab"
Purpose: To use calorimetry to determine the heat of formation of calcium hydroxide (knowing that the heat of formation of H2O(l) is -286 kJ)
Tomorrow in class we will discuss the calculations, but these are the results my group got.

Volume of H2O: 100 mL
Mass of Ca: 2.0g
Initial temp. of H2O: 21.6 degrees Celsius
Final temp of H2O: 53.3 degrees Celsius

And here's a picture of what the reaction looked like. It is a bit unclear, but the reaction was a bit hard to see in real life due to all the steam.











Today would not have been a very good day to miss, because I think it's we all had fun doing this lab today.