PChem312 s22 w11

Welcome to a week of online PChem! As you know, 11 MC students, faculty and staff are attending the 258th bi-annual ACS meeting in San Diego, CA...YES there have been 257 previous ACS meetings (2 per year). At this years meeting there are ~11,500 abstracts/presentations, ~9,000 in-person attendees, and another ~3,000 virtual registrants.

So, in my absences, i ask you to complete the following work. On Monday March 28th, you will bring to class all of the completed work listed below in a form that can be turned in, ie. hard copies.

Monday, March 21st

Worksheets from Friday...

Worksheet 1: Fuel Worksheet

Worksheet 2: Thermite Worksheet

New worksheet...

Worksheet 3: Home Heating

Tuesday, March 22nd

Welcome to an online PChem lab activity. This is a standard calorimetry lab where we determine the ΔH_rxn for three related, but different reactions. We have done previously in gen chem, but replaced it with the burning of food stuff because setting Cheetos on fire is much more exciting...now you get to do the more boring lab now.

If we were doing this in the lab, you would collect temperature vs time data for a set of three reactions:

NaOH (s) --> NaOH (aq)

NaOH (s) + HCl (aq) --> NaCl (aq) + H₂O (l)

NaOH (aq) + HCl (aq) --> NaCl (aq) + H₂O (l)

The data would look like this (collected by A. Trenttin - Fall 2020):

These reactions are done in a "coffee cup calorimeter" and although the insulating properties of the cups is not great (notice the temperature drops after reaching a max), we can compensate for this by carrying out the T_f analysis shown on the graph. By fitting the data to identify the rate of heat loss, we can determine the T_f values indicated on the graph.

Additional Data

Reaction 1 - data

NaOH (s) --> NaOH (aq)

- 100 mL of DI H₂O

- 3.51 g NaOH --> (40.00 g/mol) --> 0.0878 moles NaOH (s)

- ΔT = 34.4 - 22.0 = 12.4 ^oC

Reaction 2 - data

NaOH (s) + HCl (aq) --> NaCl (aq) + H₂O (l)

- 100 mL of 1.00 M HCl (aq)

- 3.43 g NaOH --> (40.00 g/mol) --> 0.0856 moles NaOH (s)

- ΔT = 35.8 - 22.0 = 13.8 ^oC

Reaction 3 - data

NaOH (aq) + HCl (aq) --> NaCl (aq) + H₂O (l)

- 50.0 mL of 1.00 M HCl (aq)

- 50.0 mL of NaOH (aq) containing previously dissolved 1.76 g NaOH --> (40.00 g/mol) --> 0.0440 moles NaOH (s)

- ΔT = 23.9 - 22.0 = 1.9 ^oC

Use the data above to calculate the ΔH_rxn for all three reactions. - So where do you start?

First determine how much heat was generated from the reaction by using the standard q = mass * sp heat * ΔT.

Second, this heat was generated from a specific amount (moles) of NaOH...q/mole NaOH = ΔH_rxn...repeat for all three.

Please show all of your work...Done.

Wednesday, March 23rd

Read the section in your Textbook about Hess' Law. Use the three reactions discussed yesterday to show how Hess' Law applies to this data.

Friday, March 25th

PLEASE stay tuned...we may have class on this day depending on our return travel plans.