CHEMISTRY COMMUNITY

Hedi Zappacosta 1E

As the concentrations of the reactants decreases, the rate will decrease since rate is dependent on reactant concentration

Hedi Zappacosta 1E

We are looking at the limiting reactant, or the one that reacts more slowly

Hedi Zappacosta 1E

It just depends which side of the equation you isolate. If you move the ln expressions to the right, then you will end up with the ln[A0] on top

Hedi Zappacosta 1E

The order of a reaction is determined by adding up all the exponents in the rate law.

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You can use this to find the rate of decomposition or formation of the reactants and products by dividing or multiplying their molar coefficients respectively.

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You need to know the unique rate of reaction, and from there you divide by the molar coefficient of the molecule you are finding the decomposition rate of.

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Thermodynamics can never tell us the rate of a reaction. often times we use a combination of thermodynamics and kinetics to fully understand a reaction.

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This is because E cell is the reduction potential. If you are looking at an oxidation reaction, you have to flip the sign of the reduction potential

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If the reduction or oxidation reaction does not include a solid, then use platinum

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You set the gibbs free energy equation delta H - T x delta S equal to 0. In other words, delta G is 0 because this is the value at which the reaction will change from non spontaneous to spontaneous. If a higher value of the resulting temperature gives a negative Delta G, then the reaction will be sp...

Hedi Zappacosta 1E

The change in delta S and delta H is negligible with a change in temperature so we assume they are constant.

Hedi Zappacosta 1E

For a change in temperature when we are looking at the value of k, the change in delta S is negligible, so we don't account for it.

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We can assume they are constant because changes in temperature cause so little change in delta H and delta S

Hedi Zappacosta 1E

You should probably know the values at which delta H and delta S will create a spontaneous reaction

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A negative delta H means that it is exothermic, and usually exothermic processes are favored because they don't require extra energy

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Just look at the equation delta G=delta H - T delta S. If you plug in the numbers and delta G is negative, then it is spontaneous.

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"Q4A. During the test of an internal combustion engine, 3.00L of nitrogen gas at 18.5 degrees C was compressed suddenly (and irreversibly) to .500L by driving in a piston. In the process the temperature of the gas increased to 28.1 degrees C. Assume ideal behavior and 1.00 mole of nitrogen gas....

Hedi Zappacosta 1E

All you really need to pay attention to is whether the pressure, volume, or temperature is constant.

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If you ever are given two reactants that form a product and the answer to the question is dependent on how much the reaction proceeds, you should calculate the limiting reagent.

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The polystyrene calorimeter is an open system. heat can leave. But a bomb calorimeter is closed and isolated

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You just have to read the problem and consider the variables that are being kept constant. If volume is constant, use Cv and if pressure is constant, use Cp and so on. specific heat capacity and molar heat capacity are the same. It should say in the question whether youre dealing with moles or grams.

Hedi Zappacosta 1E

I dont remember Dr. Lavelle mentioning anything about bond angles

Hedi Zappacosta 1E

delta h = the change in internal energy + P delta V. The change in internal energy also equals q + w, and w equals -P delta V. so, at constant pressure and volume, the -P delta V and + P delta V cancel out, leaving you with just delta H = q.

Hedi Zappacosta 1E

Usually they'll give you units for everything so if there are grams in the units then use specific heat capacity and if there are moles use molar heat capacity

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for the elements, you can look at the periodic table. usually it says what state each element is in at 25 degrees celsius and 1 atm.

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To convert from Celsius to Kelvin you simply add 273. Since specific heat is the amount of heat required to raise something 1 degree celsius, it is the same as raising it one Kelvin because the difference between 1 degree and 2 degrees celsius is the same as raising it from 274 to 275 degrees Kelvin...

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If you are dealing with a very weak acid or base, then you can assume that x is negligible and eliminate the x from the denominator of your Ka equations, leaving you with x^2/the original concentration of the acid or base. To check if it was correct to assume that x was negligible, check the percent...

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14-pH equals the pOH

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I think that Ka2 is always smaller than Ka1 and you have to do each dissociation as its own problem, using Ka1 for the first and Ka2 for the second dissociation.

Hedi Zappacosta 1E

Dr. Lavelle never went over this in lecture as far as I can remember so I don't think we need to worry about that.

Hedi Zappacosta 1E

In lecture, Dr. Lavelle explained that adding heat to an endothermic reaction will favor the formation of products and adding heat to an exothermic reaction will favor the formation of the reactants.

Hedi Zappacosta 1E

you can find out whether a reaction is at equilibrium using Q if you are given K. Calculate Q, and if the number is equal to K, then the reaction is at equilibrium.

Hedi Zappacosta 1E

if you change the concentrations of the reactants or products, the reaction will balance itself back to equilibrium, and the final concentrations of the reactants and products will yield the equilibrium constants if put into the equation.

Hedi Zappacosta 1E

Also, if you are calculating the reverse like 10^1.558, then the answer would be 36.1 because you only use how many sig figs are after the decimal in the exponent

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You add up the charges of all the ligands and the ions outside of the brackets. for example, if that number adds up to 2- and the charge of the total molecule is 0, then the charge of the metal is 2+.

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For part a, for example, NH3 is a base because it has a lone pair of electrons on the Nitrogen which wants to accept an proton. HBr is a bronzed base because it wants to donate its hydrogen. KOH will dissociate and accept a proton and turn water into OH-. Im not sure if I am explaining this correctl...

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Alkali metals are in group 1 and alkaline earth metals are in group 2. Both of them form base compounds. For example NaOH and KOH are from the alkali metals and CaO and Mg(OH)2 are from the alkaline earth metals.

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basically, if you have a transition metal as your central atom and you need to find its oxidation state, then you add up the oxidation numbers of all the atoms attached to it and subtract it from the total charge of the molecule.

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A lone pairs repel a bonding pair more than a bonding pair repels a bonding pair. Two lone pairs have the highest level of repulsion, then a lone pair and a bonded pair, and two bonded pairs have the lowest level of repulsion.

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Axial atoms are the atoms that form a 180 degree angle. For example, in a trigonal bipyramidal molecule, the axial atoms would be the two atoms that form the points of the pyramid. In this example, the equatorial atoms would be the ones that form the base triangle at the equator of the axis.

Hedi Zappacosta 1E

Dr. Lavelle said that if. a molecule has Nitrogen in it and that Nitrogen has a lone pair then it acts as a base. It is like in a DNA molecule where the nitrogen in the base pair gives up its lone pair.

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Can someone explain pi and sigma bonds and how to determine which is which?

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A good example of this is water. Without the lone pair on the Oxygen atom, the molecule would be nonpolar. However, the extra electrons give the molecule a bent shape, making it polar.

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I think so. Everything we've learned after the material that was on the midterm.

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To determine bond angles you have to first determine the shape of the molecule by drawing the lewis structure and looking at how many bonding pairs and how many lone pairs of electrons it has. From there, you can determine the angle based on the shape and the position that each atom is in.

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Dr. Lavelle said that we wouldn't be drawing the models with wedges, so I don't think you have to worry about that.

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it depends on how big the molecules are and how far apart the polar ends of each molecule are. For example, in dipole-dipole interactions, two spheres will have a weaker interaction because the positive end of one will be further from the negative end of the other. But, with two rod shaped molecules...

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Bond angles are determined by the largest angle between to atoms in a molecule. It is dependent on how many bonds are in the molecule. For example, a molecule with two bonds coming off of the central atom will be linear, as a 180 degree angle is the largest possible angle between these two bonds.

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Dr. Lavelle started going over this in lecture today. The shape of a molecule is always dependent on bonds being as far away from each other as possible. For a molecule with a central atom that has two bonds, it will be linear because the bonds will be farthest apart at 180 degrees. For a molecule w...

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usually the lone pairs get attached to the central atom which, in this case, is iodine.

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It is whichever atom is the least electronegative or has the lowest ionization energy.

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Hi! I was doing one of the homework problems (1A.15 in edition 7) and the question asks you to find the values of n for the initial and final energy levels of an electron where a line is formed in the UV spectrum at 102.6 nm and energy is emitted. The answer says that the initial n is 1 and the fina...

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Ionization energy and electronegativity follow the same trends on the periodic table, so it doesn't matter which one you use to determine the central atom. It should be the least electronegative and the one with the lowest ionization energy.

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A molecule is most stable when the formal charges all all the atoms in the molecule are zero. The formal charges of all the atoms will also always add up to the total charge of the molecule. Another rule is that if the formal charge of an atom in a molecule has to be negative, make sure the most ele...

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The most common ones are Sulfur and Phosphorous.

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I'm assuming you could use the equation $\upsilon =c/\lambda$

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What is the difference between atomic and molecular spectroscopy?

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It is possible for electrons to have wavelengths and frequencies. The De Broglie equation is used to calculate the wavelength of particles (including electrons), and if something has a wavelength, it will also have a frequency by nature.

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This is just something you have to memorize. The s orbitals only have one shell, P orbitals have 3, d orbitals have 5 shells, and f orbitals have 7.Each shell holds 2 electrons.

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For part d, higher frequency light has higher energy, so the energy of the photons in that light may be higher than the work function, giving the electrons emitted a higher energy. It is shown by the equation Kinetic Energy of electron=Energy of photon-Work Function. However, not all high frequencie...

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I think it is because electromagnetic radiation is essential energy going through a space, and when frequency decreases, so will energy since frequency and energy are directly proportional by the equation E=hv

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In the UV spectrum of atomic hydrogen, a line is observed at 102.6 nm. Determine the values of n for the initial and final energy levels of the electron during the emission of energy that leads to this spectral line. This is 1A.15 in the seventh edition textbook, how do you do this?

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Ok thank you!

Hedi Zappacosta 1E

What happens to the electron if the energy of the photon is exactly the same as the work function? Is it still removed?

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I calculated the energy of the electron using the formula 1/2mv^2 and I got 1.99x10^-19 J which the answer key says is correct. I thought that by "the energy required to remove an electron from one sodium atom" the question meant the threshold energy, so why isn't the answer 150.6 kJ.mol-1...

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Light hits a sodium metal surface and the velocity of the ejected electron is 6.61 x 105 m.s-1. The work function for sodium is 150.6 kJ.mol-1 How much energy is required to remove an electron from one sodium atom? I saw this on the photoelectric effect module and thought I did it correctly, but my ...

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