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zBEZZMWo5uM-019|So we'll have 3 moles of gas in the reagents and 3 moles of gas after the reaction goes to completion in the products. |
zBEZZMWo5uM-020|So 3 moles of gas on one side, 3 moles of gas on the other side under the same conditions of volume and temperature give us the same pressure. |
zBEZZMWo5uM-021|So the total pressure is the same after that reaction occurs. |
zBEZZMWo5uM-022|The correct answer here, B. |
xVv8aSBCCi4-000|In a galvanic cell, electrons flow from high potential to low potential. |
xVv8aSBCCi4-002|And at the copper electrode, copper ions are reduced to copper metal. |
xVv8aSBCCi4-003|We can make that reaction go in the opposite direction. |
xVv8aSBCCi4-004|If we take a battery or another half cell or set of half cells that have a higher natural potential than the copper zinc. |
xVv8aSBCCi4-008|So I'm just going to put everything together in one beaker. |
xVv8aSBCCi4-009|A copper electrode, a zinc electrode, connected by an external voltage. |
xVv8aSBCCi4-013|So I still have my same designation of the electrodes in electrolysis that I did when I had the galvanic reaction. |
xVv8aSBCCi4-014|What I need to get the galvanic reaction to be overcome is a voltage greater than the standard galvanic potential. |
xVv8aSBCCi4-018|It's based on the configuration of the cells, and the shape of the electrodes. |
xVv8aSBCCi4-020|The current flow, when that occurs, is measured in amps. |
xVv8aSBCCi4-021|An amps, one ampere, symbol A, is one Coulomb of charge per second. |
xVv8aSBCCi4-022|So I can measure the current flow in amps in an electrolytic cell that forces a galvanic cell to go in reverse. |
6Bnu5c_-Bpo-001|I can plot chemical reactions on a reaction profile. |
6Bnu5c_-Bpo-002|And when I do, this reaction coordinate tells me the progress of the chemical reaction. |
6Bnu5c_-Bpo-003|But this is not a time coordinate. |
6Bnu5c_-Bpo-004|This reaction coordinate is the progress of the reaction, which could go in a few seconds or 1,000 years. |
6Bnu5c_-Bpo-007|Here, a product building up over time. |
6Bnu5c_-Bpo-008|So this part of the plot, as the concentrations are changing, and I'm approaching equilibrium, is the domain of kinetics. |
6Bnu5c_-Bpo-014|Here's a reaction proceeding more rapidly. |
6Bnu5c_-Bpo-015|The concentration's building up more rapidly, as a function of time, and achieving equilibrium at an earlier time. |
9GuHD1DtCPA-000|Let's do a calculation where we estimate the enthalpy of a chemical reaction using bond enthalpies. |
9GuHD1DtCPA-001|So the reaction of the formation of benzene from three moles of acetylene. |
9GuHD1DtCPA-002|Now, when we do these we're going to use bond enthalpies, so we'll think of all the bonds that are broken and all the bonds that are formed. |
9GuHD1DtCPA-003|So the bonds that are broken in the chemical reaction would be all the bonds in the acetylene. |
9GuHD1DtCPA-004|And all the bonds formed would be all the bonds in the benzene. |
9GuHD1DtCPA-008|I have to break 6 moles of carbon hydrogen bonds, because there's 2 carbon hydrogen bonds and each acetylene. |
9GuHD1DtCPA-012|And this is one of the strengths of using bond enthalpies to estimate chemical reactions. |
9GuHD1DtCPA-013|Very frequently in chemical reactions it's only one or two bonds that are really changing. |
9GuHD1DtCPA-014|So if you know a few bond energies, you can calculate the enthalpy for a lot of reactions just because a simple chemical reaction occurs. |
9GuHD1DtCPA-015|In this case, I have alternating double and single bonds. |
9GuHD1DtCPA-016|And depending on which table you look at, you might find a delocalized carbon carbon bond. |
9GuHD1DtCPA-017|But that's not very common. |
9GuHD1DtCPA-018|I actually just remember the double and single bonds. |
9GuHD1DtCPA-022|I have to break all these bonds. |
9GuHD1DtCPA-023|That's an endothermic step. |
9GuHD1DtCPA-024|I put energy in. |
9GuHD1DtCPA-025|The amount of energy I have to put in? |
9GuHD1DtCPA-026|2,511 kilojoules. |
9GuHD1DtCPA-031|So just by knowing a few bond enthalpies, I can calculate enthalpies for a wide variety of chemical reactions. |
V5mlJRNZ0m4-000|Let's look at the standard state-free energy difference for a chemical reaction, the atomization of H2. |
V5mlJRNZ0m4-001|I can write the chemical reaction H2 molecules breaking down into H2 atoms. |
V5mlJRNZ0m4-005|What is the enthalpy difference for this chemical reaction? |
V5mlJRNZ0m4-006|Well, I don't really have to go to a table or look anything up because all that is happening here is I'm breaking the hydrogen-hydrogen bond and making hydrogen atoms. |
V5mlJRNZ0m4-007|And if you break a bond, that requires energy. |
V5mlJRNZ0m4-010|What about delta S? |
V5mlJRNZ0m4-011|I can also get delta S without looking at a table or doing a calculation because all I need is the sign of delta S, not the magnitude, just like delta H. |
V5mlJRNZ0m4-012|So delta AS is positive for this. |
V5mlJRNZ0m4-013|I'm going from one molecule to two atoms. |
V5mlJRNZ0m4-014|I'm increasing the number of particles. |
V5mlJRNZ0m4-015|When I increase the number of particles, I increase the number of microstates. |
V5mlJRNZ0m4-019|And delta S is positive, so T is always positive. |
V5mlJRNZ0m4-020|So this negative sign means the slope will be negative. |
V5mlJRNZ0m4-022|So this is just a sketch of what the plot of delta G standard versus T looks like for the atomization of hydrogen gas. |
ULdcQkZeRlA-000|The reaction of breaking a bond is an interesting one to look at. |
ULdcQkZeRlA-002|In order to break it, you have to overcome that, put energy in. |
ULdcQkZeRlA-003|It's an endothermic, or up-hill, energetic reaction. |
ULdcQkZeRlA-007|So bonded molecules, atoms bonded together in molecules, are downhill from free atoms. |
ULdcQkZeRlA-008|And that fits together with our picture of the universe. |
ULdcQkZeRlA-009|When we look around us, we find atoms more commonly in molecules bonded together. |
ULdcQkZeRlA-010|So that's the down hill, or lower, energy state of molecules is the bonded together state. |
ULdcQkZeRlA-012|So this one we can take to the bank. |
ULdcQkZeRlA-013|It's always true. |
ULdcQkZeRlA-014|If you break a bond, you always have to put energy in. |
ULdcQkZeRlA-015|It requires energy, and forming bonds always releases energy. |
dQtNrUa5Az0-000|Hi. |
dQtNrUa5Az0-001|Today, we're going to talk about atomic structure. |
dQtNrUa5Az0-002|Now an atom, as you may know, is the tiniest particle that retains the properties of an element. |
dQtNrUa5Az0-003|I have an element here, pure carbon. |
dQtNrUa5Az0-004|Now, how can we get down to atoms. |
dQtNrUa5Az0-005|Well, you could do a thought experiment or a Gedanken-experiment, as Einstein used to say. |
dQtNrUa5Az0-006|That's an experiment that you can't actually do, but you can perform it in your mind to help you think about a concept. |
dQtNrUa5Az0-007|So here's a Gedanken-experiment. |
dQtNrUa5Az0-008|Take this piece of carbon, cut it in half. |
dQtNrUa5Az0-009|And then take that half and cut it in half again. |
dQtNrUa5Az0-010|And take that half and cut it in half again. |
dQtNrUa5Az0-011|If you keep cutting it in half, eventually you'll get down to a tiny piece of carbon that retains the properties of carbon. |
dQtNrUa5Az0-012|If I cut it in half again, I don't have carbon anymore. |
dQtNrUa5Az0-013|Now, that tiniest piece that retains the properties of carbon, that would be an atom of carbon. |
dQtNrUa5Az0-014|What's an atom composed of? |
dQtNrUa5Az0-016|It's positively charged, because it contains protons. |
dQtNrUa5Az0-017|Protons contain a positive one electrical charge. |
dQtNrUa5Az0-018|Now a proton is very important for the nucleus, because the proton is the single defining factor that determines the identity of the element. |
dQtNrUa5Az0-019|If you have one proton in your nucleus, you are a hydrogen atom. |
dQtNrUa5Az0-020|If you have six protons, you're a carbon atom. |
dQtNrUa5Az0-021|I don't care what else is in the Nucleus, six protons you are carbon. |
dQtNrUa5Az0-022|So what else is in the nucleus then? |
dQtNrUa5Az0-023|Well, nuclei often contain neutrons. |
dQtNrUa5Az0-024|Now neutrons are not charged as their name implies. |
dQtNrUa5Az0-025|They're neutral particles. |
dQtNrUa5Az0-026|They simply add to the mass of the atom, but they don't change the identity of the element, and that's very interesting. |
dQtNrUa5Az0-027|You can have carbon that has different masses. |
dQtNrUa5Az0-028|It's just the protons that determine the element carbon, but with different numbers of neutrons, you'll have different masses, all of them carbon. |
dQtNrUa5Az0-030|And in the neutral atom, there's an electron for every proton in the nucleus. |
dQtNrUa5Az0-031|That is the charges balance out, so you have neutral atoms with an equal number of protons and electrons. |
dQtNrUa5Az0-034|We can give it the atomic mass, and we can give it the atomic number. |
dQtNrUa5Az0-035|The atomic number is the number of protons in the nucleus. |
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