CHEMISTRY COMMUNITY

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*high five*

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H+ is used to balance acidic solutions, OH- is used to balance basic solutions. One can't be used for the other because there is no concentration to use, and that form of the reaction is highly unlikely to happen.

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A catalyst is a reactant in the first step, and a product in the second step. It lowers activation energy, and speeds up a reaction.

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A second order reaction is one that either has two different reactants that change the rate of the reaction, or has two moles of the same reactant that changes the rate of the reaction. ex) (H+) + (OH-) --> H2O is a second order reaction because the rate of the reaction depends on both H+ and OH-. T...

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There are many ways a reaction can become first or second order, but the main difference is how many reactants the rate depends upon. If the rate depends on one reactant, then it is first order. If the rate doesn't depend on a reactant (say it depends on a catalyst instead) then the reaction is zero...

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Yes, it is because you have to account for the fact that the rate = A^{2} . From this equation, you can get the half-life equation which is t_{1/2}= \frac{1}{k[A]_{0}} . From this equation you can clearly see that with respect to [A], the half-life has an inverse relationship, so the plot won't be ...

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Stoichiometric coefficients aren't used when determining rate order because experimentally, concentration and time are the only things being considered, so rate order is based on each reactant, not how many moles of that reactant are reacting.

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Being spontaneous means the reactants have more energy than the products, so there's energy to be released. If it was the other way around, then energy would have to be input for the reaction to start.

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When catalysts/enzymes are saturated they can only work so fast. Adding more reactant won't affect the reaction rate because the catalyst/enzyme is already working as fast as it can (at that temp/pressure/acidity/etc.) This means the reaction rate is independent of concentration of reactant and it i...

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If it is a multi-step reaction and one is significantly slower than the other, then we will always use that step to determine the rate-law.

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Most of the time it will tell you, but if it asks you to determine which step is the slow step, then it's the one the rate law is describing. This rate law can be derived from concentrations and time as well, so be ready to derive the slow step from a table of concentrations and times.

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I think we should be ready for anything. We've spent a lot of time in class on derivations and integrations, so I wouldn't be surprised if he asks us to derive something at some point. It shows a true understanding of the material, and is something that could only be helpful to know!

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They're going to give you enough to solve the problem. Most of the time it will be concentrations and rates, sometimes they might give you k and n and have you solve for something else, just be ready for anything.

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Thermodynamic stability is determined by somethings Gº value. The lower its Gº, the more stable it is going to be. If it is a reactant in a reaction, then the lower its Gº, the less likely it is going to be a spontaneous reaction.

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If the book says its in molar form, then I'm pretty sure we would take deltaG and divide it by the number of electrons being transferred in the reaction. This would turn the energy from KJ into KJ/mol, however I'm not sure, could someone confirm?

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Galvanic and Voltaic cells are the same thing. They are related through the equation deltaGº = -nFEº, where n is number of moles of electrons being transferred by the reaction, and F is Faraday's constant, 9.6485X10^4 Colombs/mol.

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For the most part, with a bit of practice, it becomes easier to tell which is being oxidized and which is being reduced. We know O and H, all alkali metals, and all halogens will be unchanging for the most part, so we are looking for transition metals. Once we know the molecule with the transition m...

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F is faraday's constant, for the most part we will be using 9.6485 X 10^4

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Electrons must be forced into the system in order for a galvanic cell to be reversed. We know this because we have to do it, it will not happen by itself. If we are looking for if a galvanic cell is working, we need to run the current through something and test it, such as a voltmeter or a lightbulb.

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An example of this would be solid vs liquid of the same material. Inputting energy into the system will make the solid turn to liquid, but they can be the same temperature.

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I think in real life examples it isn't realistic, but if something is constant in a problem, there will be some way for you to tell, whether they tell you or they tell you something about the system that hints at it.

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Yes because there is no way for energy to flow through it, so deltaU is 0, but w and q are also 0 because there is no way for energy to enter or leave, so they can't be balanced either.

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Basically how a cell works is that it separates two materials that can create a redox reaction, but allows them to be connected by a material that can conduct electricity. When this connection is made, the two species are allowed to react, and electrons flow through the circuit, powering it. When th...

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For the most part, O will always be -1, halogens will always be -1, and H will always be +1. Once we assign values to these elements, then the rest we just add up the rest of the molecule to equal the total charge.

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Assuming it's still the expansion of an ideal gas, heat will have to be entering the system. According to Charles law, we know the volume of a gas is inversely proportional to its temperature, so for a gas to increase in volume but stay the same temperature, heat energy must be entering it.

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Yes Exactly! To determine degeneracy we use # of states^ # of particles, so if there is a mol of something it would be ^6.022X10^23

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Degeneracy in the case of thermo is relating to entropy. The more ways molecules can be ordered the more entropy it has, and the more entropy a species gains from a reaction, the more favorable that reaction is.

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Yes exactly, when ΔG is negative the reaction is favorable, and when it is positive it is unfavorable.

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If the temperature is constant, we have to use the equation S=nKln(V2/V1), reversible or irreversible. A reversible change can happen without a constant temperature, but if the pressure is constant, we have to use different equations depending on what is constant.

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If it happens slowly, tiny steps at a time, it is reversible. If it happens very quickly, and some of the energy is lost, it is irreversible.

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For the most part you will have to figure out if it is a closed open or isolated system, but there are some easy examples to know, anything open is open, anything with a cap on it is closed, and anything insulated and capped is isolated. A bomb calorimeter is also isolated. Hope this helped!

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It's necessary to identify this because we treat the systems differently. For example, in an open system, there will always be constant pressure, so we can treat q as deltaH, where as in a closed system or isolated system, this may be different.

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It all depends on what you set your system as. If you have a beaker and a piston and your system in just the piston, then the beaker would be losing energy and the piston is gaining energy, this means the beaker is putting positive work on the piston. If your system is the beaker AND the piston, the...

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Yes those are both ways to increase energy in an open system. Ways to increase or decrease energy only become more restricted as the system becomes more isolated. The more open a system is, the more ways there are to increase the energy of that system.

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All we know so far is that ΔU = q + w what we don't know yet is what q is when pressure is not constant.

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When the piston moves out, something has to push it out. Assuming nothing from the outside is pulling it out, something on the inside must be using energy to push it out, so the system must be losing energy.

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No, solids and liquids are both put in as 1. The only things that can have value are aqueous (aq) and gas (g).

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H is calculated by taking final-initial, if the final has less H than the initial (-), then that energy had to go somewhere, it was released into the world, exothermic. If the final has greater H than the initial, then it needed energy from somewhere and was absorbing energy from the outside world (...

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Enthalpy is just the measure of heat! Temperature and enthalpy are related but are different, as seen in heat curves. The x-axis is heat supplied and the y-axis is temperature How are heat and enthalpy different? Heat is more of a descriptor, we can feel heat and know what it is and how to describe...

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Calories are 1000 calories.

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When heating up a material, the energy can go into two places, increasing the temperature (specific heat), or changing the phase (heat of vaporization). Steam may not be more hot compared to boiling water if they are both 100ºC, but it will be carrying more energy because of the energy input in orde...

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The ideal gas law takes into account many assumptions. The most important ones are all collisions are elastic, the molecules themselves don't take up space, and there is no interaction between gas particles except for collisions. These assumptions work best at low pressure and at high temperatures. ...

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p before anything means to take the -Log of that thing. pH and pOH are the -log of the H concentrations and the OH concentrations. We can use the K equation to solve for the concentrations. We know we're solving for pH or pOH depending on if the reaction we are using, whether its a weak base or weak...

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This is called the X is small approximation. Relative to the initial concentration, the change is so small, less than 10^-3 smaller, so we can treat it as the same number before and after without significant change. This makes our math much, much easier.

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Concentrations don't effect the K value in itself, but can effect the direction of the reaction. Only temperature can change the K value.

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A buffer resists changes to pH, it is usually made out of a weak acid and a salt containing the weak acids anion.

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Liquids are pure substances and therefor cannot have a concentration. To have a concentration there needs to be a solute in a solvent, 2 substances, liquids are only 1 substance.

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Q is just a method to determine which way the reaction is going to go. The equation has products over reactants, so when there are more products, Q is larger, when there are more reactants Q is smaller. If we let any reaction sit for a while, it will eventually reach K, this means that if Q>K, there...

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Pressure alone doesn't change the equilibrium constant. The reason there is a change when we "increase pressure" is actually due to the decrease in volume, and change in concentrations of those initial gases. Adding an inert gas that will have no effect on the reaction doesn't change the e...

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The brackets represent molarity, and the P represents partial pressure. The only time to use P is when we are dealing with gasses, it should be (g) as a subscript in the chemical equation this calculates Kp. If it has an (aq) it is a solution with a concentration, and we can use the bracket, this ca...

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They are both units of pressure, so as long as all the units match up you should be good to go.

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