CHEMISTRY COMMUNITY

Diana Bibireata 1B

After you find the x values, you plug it into the ice table. Only one of the values will give an answer that makes sense because the other x value will give a negative equilibrium concentration, which is not possible.

Diana Bibireata 1B

If the problem does not specify what units your answer should be in then it doesn't matter which one you use.

Diana Bibireata 1B

Partial pressure is usually given in either atm or bar.

Diana Bibireata 1B

The standard reaction enthalpy is just the enthalpy when all reactants and products are in their standard state at 1 atm.

Diana Bibireata 1B

A catalyst lowers the activation energy so it ends up speeding up the rate of the reaction.

Diana Bibireata 1B

If the given K value is less than 10^-3 then you can use the approximation method where x is so small that the change it causes to the equilibrium concentration is negligible.

Diana Bibireata 1B

For acidic solutions you balance out the oxygens by adding H2O and you balance the hydrogens by adding H+. For basic solutions you balance the oxygens by adding H2O and then you balance the hydrogens by adding H2O to the side that requires more H atoms and add the same amount of OH- to the other side.

Diana Bibireata 1B

When doing calculations you should always convert temperature into kelvins. In general just keep track of the units at all times because some of the constants on the constants and equation sheets (such as specific heat capacity) are given in celsius so be mindful of that.

Diana Bibireata 1B

Delta G is the change in Gibbs free energy. The equation commonly used is: delta G = delta H - T(delta S). Gibbs free energy is also a state function.

Diana Bibireata 1B

A loss of electrons is oxidation, a gain of electrons is reduction. If the charge increases then electrons were removed so it would be considered oxidation.

Diana Bibireata 1B

A positive cell potential indicates the reaction is spontaneous as written for the given conditions.

Diana Bibireata 1B

The textbook states that you include an inert electrode such as platinum when the electrode reaction does not include a conducting solid as a reactant or product.

Diana Bibireata 1B

Pressure and volume are inversely proportional so (P1/P2) = (V2/V1).

Diana Bibireata 1B

A state function only depends current conditions, not the path it takes to get there.

Diana Bibireata 1B

When there is a phase change you use the equation S = qrev/T because the temperature is constant. You use S = nClnT2/T1 when the temperature does change.

Diana Bibireata 1B

If work is done on the system, w is positive because the energy of the system has increased. If work is done by the system, w is negative because the energy of the system has decreased.

Diana Bibireata 1B

In an isolated system, matter and energy are not exchanged with the surroundings. Therefore the internal energy remains constant, so deltaU is 0.

Diana Bibireata 1B

Heat capacity is the heat required to raise the temperature of an object by 1 degree C.
Specific heat capacity is the heat required to raise 1g of substance by 1 degree C.
Molar heat capacity is heat required to raise 1 mol of substance by 1 degree C.

Diana Bibireata 1B

The system is the object of interest and the surroundings is anything else, so there is no boundary to the surroundings. Essentially the system + surroundings = universe.

Diana Bibireata 1B

In a closed system, energy can be exchanged with the surroundings. In an isolated system, neither matter nor energy can be exchanged with the surroundings.

Diana Bibireata 1B

In the process of phase change (in this case vaporization) the temperature doesn't change (stays at 100C). However, when making steam, there is still heat and energy being added to break the bonds, which is why steam causes severe burns.

Diana Bibireata 1B

If you use the approximation method when using an ICE table, the x value you get needs to be less than 5% of the initial concentration for this method to be valid.

Diana Bibireata 1B

The modules are optional. The post assessments are pretty helpful however if you want extra practice.

Diana Bibireata 1B

You use ICE tables to find the concentrations at equilibrium because the whole point of an ICE table is to show the initial concentration, the change in concentration, and the equilibrium concentration. To find Q you just find the ratio of products to reactants at any point during the reaction.

Diana Bibireata 1B

Both K and Q are calculated the same way. K just describes the reaction at equilibrium and tells us whether there are more products or reactants at equilibrium. Q can be calculated at any part of the reaction and is used to determine the direction which a reaction will proceed.

Diana Bibireata 1B

Because the K value is so small you can use the approximation method. In this case the x value will be so small that you can assume the value (0.1-x) will be approximately equal to 0.1. You can use this method whenever K is less than 10^-3.

Diana Bibireata 1B

If the K value is very small (less than 10^-3) then you can use the approximation method where you assume that x is so small it won't make a big difference. If the x value you get is less than 5% of the initial concentration, then using the approximation method is valid. Otherwise you need to use th...

Diana Bibireata 1B

Charles' Law simply states that the volume of a gas is directly proportional to the temperature if pressure stays constant.

Diana Bibireata 1B

Both are equally important. But keep in mind that Kp is only used for gases while Kc can be used for gases and aqueous solutions.

Diana Bibireata 1B

The molar concentrations of solids and liquids do not change in a reaction and therefore are not used to calculate the equilibrium constant. On the other hand, both gases and aqueous solutions are used to calculate the equilibrium constant.

Diana Bibireata 1B

Formal charge is useful to find the most stable lewis structure. You want the formal charge to be 0 on all atoms but if that's not possible then usually the negative formal charge goes on the most electronegative atom.

Diana Bibireata 1B

atomic radius is defined as half the distance between the centers of neighboring atoms

Diana Bibireata 1B

yes! a single bond has 1 sigma bond, a double bond has 1 sigma and 1 pi bond, and a triple bond has 1 sigma and 2 pi bonds.

Diana Bibireata 1B

A trigonal planar molecule has 3 regions of electron density. the regions of electron density is equal to the number of hybrid orbitals. Therefore a trigonal planar molecule has a hybridization of sp2 (a hybrid of 1 s orbital and 2 p orbitals).

Diana Bibireata 1B

A bronsted acid is a proton donor and a bronsted base is a proton acceptor. A lewis acid accepts an electron pair and a lewis base donates the electron pair. Both essentially mean the same thing however the lewis definition is a little more general. In the example: NH3 + H2O → NH4+ + OH- a hydrogen ...

Diana Bibireata 1B

when using the VSEPR model, you can essentially use the lewis structure to see how many lone and bonding pair electrons there are around the central atom to determine the AXE formula. From there you can describe shape, bond angles, polarity etc.

Diana Bibireata 1B

Its because the additional bonding electrons in a double bond attract the nuclei more strongly and pull the atoms closer together.

Diana Bibireata 1B

The electrons in double and triple bonds stay together and repel other bonds/lone pairs as a single unit so you treat it as just one region of electron density.

Diana Bibireata 1B

When there is a difference between the electronegativity of two atoms a partial charge forms. The atom with more pulling power has a greater share of electrons so it has a negative partial charge which means it has a negative dipole.

Diana Bibireata 1B

The VSEPR model accounts for bond angles and molecular shape. Regions of high electron concentration in a molecule repel one another so these regions move as far as possible to minimize repulsions.

Diana Bibireata 1B

When there is a difference between the electronegativity of two atoms a partial charge forms. The atom with more pulling power has a greater share of electrons so it has a negative partial charge which means it has a negative dipole.

Diana Bibireata 1B

A multiple bond is just treated as one region of electron density. The electrons in double and triple bonds stay together and repel other bonds/lone pairs as a single unit.

Diana Bibireata 1B

In the trigonal pyramidal molecular shape there are three bonds and one lone pair on the central atom. This is the best shape because the lone pair on the central atom distorts the molecular shape to reduce lone pair-bonding pair repulsions. I'm sure this will be covered more in future lectures!

Diana Bibireata 1B

In larger atoms the outermost electrons are less tightly held because the nucleus exerts a weak control over these electrons. Therefore they are easily distorted.

Diana Bibireata 1B

In larger atoms, electrons are less tightly held because they are further from the nucleus which is why they are easily distorted

Diana Bibireata 1B

The electrons in the Hg atom have discrete energy values so they can only emit certain wavelengths of light.

Diana Bibireata 1B

The book states that "multiple bonds are shorter than single bonds between the same two elements because the additional bonding electrons attract the nuclei more strongly and pull the atoms closer together" (7th ed. pg 100)
Hope this helps!

Diana Bibireata 1B

It is one of the homework problems and I think anything that shows up on the homework is fair game for the test.

Diana Bibireata 1B

You do not need to fully memorize the electromagnetic spectrum but it may be helpful to know that visible red light is about 700nm and visible violet light is about 400nm because that was covered in lecture.

Diana Bibireata 1B

Yes, know that the s orbital has no nodal planes, the p orbital has 1 nodal plane, and the d orbital has 2.

Diana Bibireata 1B

The textbook says that if something is degenerate it has the same energy. For example, atomic orbitals that are in the same sub shell.

Diana Bibireata 1B

Essentially in a nodal plane no electrons will be found. You should know how many nodal planes there are for each orbital (no nodal planes in s orbital, 1 in p orbital, simplest d orbital has 2, etc.)

Diana Bibireata 1B

For part a you use the equation $E=ch/\lambda$
(because c and h are constants and the problem gives you the wavelength). This gives you the energy of a sodium atom. Then, for part b, after you find the number of atoms of sodium, you simply multiply it by the energy of one sodium atom.

Diana Bibireata 1B

The DeBroglie equation only applies to particles with resting mass (for example electrons) that has momentum (p). You can't use this equation for something like light because light has no mass when at rest.

Diana Bibireata 1B

In the equation c= $\lambda \nu$ you do use meters (because the unit for c is meters per second)
But it is important to note that wavelengths in the visible spectrum are usually given in nanometers (which is 10^-9m) so just also know this conversion.

Diana Bibireata 1B

Essentially each photon needs to have more energy than than the energy to remove an electron from the metal (aka the threshold energy). So if 1000 photons hit the metal surface and each individual photon has enough energy, then 1000 electrons will be released.

Diana Bibireata 1B

In this problem they give you the wavelength so you use the equation \nu =c/\lambda to find the frequency. Then you want to use the Rydberg equation which is \nu =R(1/n_{1}^{2}-1/n_{2}^{2}) . Your n 1 value will be 1 because it is in the uv spectrum so it is a part of the Lyman series. From ...

Diana Bibireata 1B

NH₄⁺ (ammonium) and H₂PO₄^- (dihydrogen phosphate) are polyatomic ions which is why they wrote it like that.

Diana Bibireata 1B

I noticed that too and I believe the answer key is correct and the reactant should be Fe₃Br₈. This would make sense because the product from the second reaction should be one of the reactants in the 3rd reaction.

Diana Bibireata 1B

In the end you will have to memorize them but there are a few ways that will make memorizing them easier. 1. polyatomic ions ending with -ate have one more oxygen atom than those ending with -ite. (ex. nitrate: NO 3 - and nitrite: NO 2 - ) 2. ions with per- have one more oxygen atom then those endin...

Search found 60 matches