0:02 so the last section of the book that
0:04 we're going to cover this semester is
0:07 about ionic strength and uh I strengths
0:10 of ionic and coal bonds so after this
0:12 section you should be able to describe
0:15 the energetics of ionic and calent bond
0:18 formation uh through form Bond formation
0:22 and breakage then we are going to do um
0:25 a born habber cycle to compute lattice
0:28 energies for IA compounds and we can use
0:32 these average bond eny to estimate our
0:34 enthalpies of
0:37 reactions so just as a reminder bond
0:40 breaking is an endothermic reaction so
0:43 whenever we break a bond this actually requires
0:52 energy so we can start off with hydrogen
0:55 we can add energy to it and then we can
0:58 actually get two individual hydrogen
1:01 atoms so we can break apart that Bond
1:05 Bond forming so whenever we form a bond
1:11 energy so we can have two hydrogens so
1:14 remember when we went way back in terms
1:15 of thinking about what happens when we
1:18 take two hydrogen atoms bringing them
1:20 close together all of a sudden the
1:23 energy drops and we form a bond so our
1:25 two hydrogens will actually form
1:28 hydrogen glass and we will release
1:31 energy and just as a rinder since this
1:33 is like hess's law and it's a state
1:36 function whether you go forward or
1:39 backwards the enthalpy is a change so
1:42 for our bond breaking this requires
1:47 436 kles for every mole of hydrogen gas
1:51 or if we look at the bond uh forming
1:53 this will release
1:57 436 kog for every two hydrogen atoms
2:00 that come together
2:02 so we can think about these con Bond
2:04 strengths in terms of coal bonds and
2:07 looking at them so we can think about
2:09 lots of these Bond energies and what
2:13 happens to these kinds of tables and the
2:15 formation so there there's a lot of
2:18 Trends in kind of looking at this one of
2:20 the trends to think about if we think if
2:24 we look at just a single Bond over here
2:28 a double bond takes more energy 6111 k a
2:31 triple bond is super super strong so in
2:35 order to break that Bond it's 300 uh
2:39 837 K and remember our bond lengths get
2:43 shorter as the bond gets stronger on
2:45 there so short bonds are going to be
2:47 much stronger and they're going to
2:48 require more
2:51 energies so in terms of thinking about
2:53 our enthalpies and our enthalpies of
2:56 reactions we can look at the enthalpy of
2:58 reaction and we can estimate it using
3:01 these kinds of tables so we can look at
3:05 the sum of all the bonds broken minus
3:09 the sum of all the bonds that are formed
3:11 so in this
3:14 example we can think about this hydrogen
3:15 we're looking at
3:20 hydrogen um and it's going to react with
3:30 HCL two of those so in this reaction we
3:33 can look at this and think about how
3:36 many bonds are actually forming and how
3:39 many are breaking so we are going to
3:42 break a hydrogen hydrogen bond we're
3:45 going to break a chlorine chlorine bond
3:51 and we are going to form two HCL bonds
3:55 so we can calculate our Delta H uh for
3:58 this our Delta H is going to be equal
4:01 the number of bonds broken SK so we look
4:04 up at the enthalpies of up here and we
4:07 have an HH is
4:11 436 um and our CL is [Music]
4:12 [Music]
4:16 243 uh right here so that's sum
4:21 436 K plus 243 I'm going to use the
4:24 bracket since we have a summation here
4:26 and we got to watch out for this
4:28 negative sign in the summation we're
4:30 going to subtract from that all all the
4:33 bonds forms we end up getting two hcls
4:36 we look HCL that's
4:39 432 so there's two times uh of those
4:46 432 and when we sum that up we end up
4:48 getting minus
4:53 185 kog for every mole of hydrogen for
4:56 every mole of chlorine and for every uh
4:59 two moles a hydrochloric acid that are
