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9z0sMWVIm7A-020|Well, in the reduction, the 2 chromium here, only 1 there, so I need a 2.
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9z0sMWVIm7A-021|And in fact, I'm just going to go through and apply the steps to the chromate first, and then come back and do it for the alcohol and aldehyde.
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9z0sMWVIm7A-024|Now I have to balance the hydrogens by adding H plus.
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9z0sMWVIm7A-030|So six pluses here and 2 times plus 3, 6 pluses there.
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9z0sMWVIm7A-031|Now, let's do the same thing for the alcohol to aldehyde, balance the elements.
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9z0sMWVIm7A-032|All the elements are balanced here, so nothing required there.
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9z0sMWVIm7A-033|Balance the oxygen with water.
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9z0sMWVIm7A-034|I have 1 oxygen on both sides, so nothing required there.
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9z0sMWVIm7A-035|Balance the hydrogens by adding H plus.
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9z0sMWVIm7A-039|Now I can bring my half reactions, now that they're balanced back together, and balance the electrons in both half cells.
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9z0sMWVIm7A-040|So this half cell, I noticed 2 electrons and I noticed that's an oxidation.
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9z0sMWVIm7A-041|6 electrons here and that's a reduction, that's good.
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9z0sMWVIm7A-042|That's what I thought was happening and my procedure has confirmed that.
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9z0sMWVIm7A-043|So, let's balance them out.
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9z0sMWVIm7A-046|I'll add the two reactions together with my factor of 3.
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9z0sMWVIm7A-050|And you can see now if you count up all the hydrogens, all the oxygens, all the chromium and carbons on this side, they exactly match up with that side.
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9z0sMWVIm7A-052|That's how we balance redox reactions.
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11QPT4cbBO8-000|Chemistry is the study of atoms, molecules, and their interactions.
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11QPT4cbBO8-001|Now, virtually every process that happens in the universe involves molecules, atoms, and their interchange.
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11QPT4cbBO8-005|So this reaction, the formation of water from hydrogen and oxygen, is favorable.
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11QPT4cbBO8-006|In fact, when that reaction occurs, energy is released.
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11QPT4cbBO8-007|It can be very dramatic.
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11QPT4cbBO8-008|So in a sense, the products, water, are lower energy than the reactants.
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11QPT4cbBO8-009|And we can plot that on a relative scale.
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11QPT4cbBO8-010|And we'll do this a lot in chemistry.
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11QPT4cbBO8-011|We'll plot energy on a vertical scale and the progress of a reaction along the horizontal scale.
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11QPT4cbBO8-013|Now, in a mechanical example, you'd say, well, if they were a ball on the top of this hill, it would naturally roll down to the bottom of the hill.
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11QPT4cbBO8-014|That's the natural way of things.
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11QPT4cbBO8-015|And it's the same for this chemical reaction.
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11QPT4cbBO8-016|The natural way is for hydrogen and oxygen to form water.
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11QPT4cbBO8-017|There's a natural favorable direction of this chemical reaction.
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11QPT4cbBO8-018|But there's one more interesting part.
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11QPT4cbBO8-019|And that is, if I take oxygen and hydrogen, and I mix them together in a balloon, I can wait quite a while and never find water.
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11QPT4cbBO8-020|I can come back and look at that balloon the next day, the next week, six months later, and it's still going to be a hydrogen oxygen balloon.
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11QPT4cbBO8-021|You won't find a balloon full of water.
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11QPT4cbBO8-022|And why is that?
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11QPT4cbBO8-024|That pulling and stretching and rearranging of bonds requires energy.
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11QPT4cbBO8-025|So there is a high energy intermediate state between the reactants and products.
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11QPT4cbBO8-027|And you might say, well, if there's that high road barrier, why do they ever react?
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11QPT4cbBO8-028|Well, let's go back to the mechanical example.
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11QPT4cbBO8-029|If I had a ball here, could I get it to the other side of that hill?
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11QPT4cbBO8-031|One way I could get it was to flick it-- give it some kinetic energy, and have it roll up over the hill.
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11QPT4cbBO8-033|So it's possible in the mechanical example.
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11QPT4cbBO8-034|Is it possible in the chemical example?
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11QPT4cbBO8-035|Well, it is.
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11QPT4cbBO8-036|I can't go in and flick individual atoms or molecules of hydrogen and oxygen, but I can get them to move faster, give them kinetic energy.
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11QPT4cbBO8-037|I can heat them up.
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11QPT4cbBO8-038|And throughout this course, we'll associate an increase in temperature with more molecular motion.
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11QPT4cbBO8-039|So I can get reactants to have enough energy that some of them will react and go over this hill.
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11QPT4cbBO8-040|And then it can become cooperative.
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11QPT4cbBO8-041|They'll release some energy.
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11QPT4cbBO8-042|they'll excite others in the mixture, and they'll all start to fall over that hill.
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11QPT4cbBO8-049|So both those would be interesting.
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11QPT4cbBO8-050|And in fact, a lot of these chemical reactions release energy, and they're fun to watch.
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11QPT4cbBO8-051|And we'll watch a lot of chemical reactions through this series.
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11QPT4cbBO8-052|The hydrogen oxygen reaction is one that I find most interesting, and I think you will, too.
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XIJet3gIKRc-000|Let's do a calculation involving a weak acid, its pKa, and determining the relative concentrations of the acid and base form.
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XIJet3gIKRc-001|So aspirin, acetylsalicylic acid has Ka, 3.2 times 10 to the minus 4.
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XIJet3gIKRc-002|A typical weak acid.
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XIJet3gIKRc-003|Now I can put it in solution and then adjust the pH to 4.13.
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XIJet3gIKRc-008|We'll just tell you what the acidic proton is unless it's very obvious.
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XIJet3gIKRc-009|So here's the acidic proton.
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XIJet3gIKRc-010|I know the acid dissociation constant for the reaction where this proton leaves the molecule is 3.2 times 10 to the minus 4.
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XIJet3gIKRc-013|I'm at a pH very close to that, really, within half a unit.
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XIJet3gIKRc-017|About equal concentrations.
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XIJet3gIKRc-018|I'm a little bit above, I'm a little bit to the basic side, of the pKa so that means the basic form will slightly predominate.
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XIJet3gIKRc-019|Not a factor of 10.
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XIJet3gIKRc-021|And we're not one full unit.
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XIJet3gIKRc-022|We'd have to go up to pH 4.49 to get a tenfold difference.
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XIJet3gIKRc-023|So we expect something less than tenfold difference.
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XIJet3gIKRc-024|Let's actually do the calculation.
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XIJet3gIKRc-025|So here's the acid and the base form, pKa 3.49.
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XIJet3gIKRc-027|In this case, we know these two, so we can solve for this ratio.
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XIJet3gIKRc-028|So let's just do that.
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XIJet3gIKRc-033|So the ratio of base form to acid form is 4.36.
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XIJet3gIKRc-034|There's about four times as much base form as there is acid form.
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8y5KX4kzt0A-000|Let's talk about the isothermal expansion and compression for an ideal gas.
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8y5KX4kzt0A-001|Isothermal means the temperature doesn't change.
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8y5KX4kzt0A-002|And if the temperature doesn't change for an ideal gas, the energy and the enthalpy don't change.
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8y5KX4kzt0A-003|Remember, the energy of an ideal gas, 3/2 nRT.
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8y5KX4kzt0A-004|So isothermal processes delta-E and delta-H are zero.
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8y5KX4kzt0A-005|So how can heat flow or work be done if the energy doesn't change?
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8y5KX4kzt0A-006|Well, the work and heat just have to balance each other with opposite sign.
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8y5KX4kzt0A-007|If you do a joule of work on the system, the system has to lose a joule of heat, joule for joule.
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8y5KX4kzt0A-008|Do a joule of work, lose a joule of heat.
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8y5KX4kzt0A-009|Do a joule of work, lose a joule of heat.
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8y5KX4kzt0A-010|If I expand, the system does work.
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8y5KX4kzt0A-011|So I do a joule of work, that would-- well, that's some of my energy, I need more energy to replace the energy I just used to do that work.
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8y5KX4kzt0A-012|Well, absorb a joule of heat.
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8y5KX4kzt0A-013|Do a joule of work, absorb a joule of heat.
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8y5KX4kzt0A-020|That's expansion and contraction isothermally for an ideal gas.
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VcGOL6Uthmw-000|Let's look at a couple of titrations and see if we can predict the equivalence point, or the end point, pH.
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VcGOL6Uthmw-004|So two acids and a base.
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VcGOL6Uthmw-005|We'll titrate them appropriately.
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VcGOL6Uthmw-006|If they're acids, we'll titrate them with a base.
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VcGOL6Uthmw-007|If it's a base, we'll titrate it with an acid.
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VcGOL6Uthmw-008|The question is at equivalence point, which has a pH less than 7?
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VcGOL6Uthmw-018|We're looking at the titration of some weak acid and base solutions.
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VcGOL6Uthmw-019|Now, when you titrate a weak acid or a weak base with a strong base or a strong acid, the titration curve looks something like this.
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VcGOL6Uthmw-020|We have the acid being converted to its conjugate base.
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