Ch6 lec 4

(4/17/20, bes)

Good morning!

If you were on campus it might have been a snow day! Maybe not, ~4-6" in Monmouth this morning and still lightly snowing.

Today will be the last lecture covering Ch 6: Thermochemistry. Remember to follow these lecture notes, the book contains MANY other topics that we did not cover in this online format. There are 2 WA associated with this chapter...one will be available at 8 am this morning. We will start chapter 7 on Monday...our third exam will cover chapters 6 and 7.

Section 6.6, the "Direct Method" only

These section is a bit different from the others in that chemistry usually makes reference to "experiments" or experimental data collected in the lab. This section discussed how we can determine the amount of heat given off (or taken up) by a reaction using...math...or theoretical methods, as opposed to experimental data. You should be familiar with the term "enthalpy of reaction," (ΔH_rxn)...this is the amount of heat involved in a reaction per rxn or per mole, etc. (see earlier notes).

In this section we are going to calculate the "enthalpy of reaction," (ΔH_rxn) under a set of standard conditions using tabulated values found in your book. When we do these calculations under "standard conditions" we add a superscript "o", as in ΔH_rxn^o. These tabulated values are called "heats of formation" and have a symbol similar to the enthalpy of reaction; ΔH_f^o. You can think of heats of formation as the amount of energy in an individual substance and when a reaction happens and reactants are turned into products the amount of heat given off (or taken up) is the difference in the amount of the energy in the reactant vs the products. So, in words, the heat given off (or taken up) by a reaction is the difference between the energy in the products minus the energy in the reactants. The math form of this statement is eq. 6.18. It is important for you to go now read the first part of this section (pages 253-255, stop after "The Direct Method")...study closely the examples and then...off to WA to work a few problems.

Have a great weekend!