CHEMISTRY COMMUNITY

Ashley Nguyen 2L

The size of the electrode should not change the potential of the cell because it is solid and the reaction quotient does not take solids or liquids into consideration

Ashley Nguyen 2L

Normally if the activation energy is higher, the reaction rate is slower because it requires more energy.

Ashley Nguyen 2L

I believe that deltaG ionization is calculated the same as normal standard gibbs free energy.

Ashley Nguyen 2L

I don't think so. I calculated Gibbs free energy ionization the same way as standard gibbs free energy.

Ashley Nguyen 2L

You would consider one specific atom within a molecule

Ashley Nguyen 2L

An integrated rate law gives the rate of reaction based on time, while a differential rate law gives the rate of reaction based on reactant concentration.

Ashley Nguyen 2L

I usually balance the O first using H2O and then balance the H using H+ afterwards

Ashley Nguyen 2L

A concentration cell has the same anode and cathode, which means that electron transfer comes from differences in concentration. When the two electrodes are connected, electrons from the cell with the lower concentration (the anode) move to the cell with the higher concentration (cathode) to create ...

Ashley Nguyen 2L

If you are referring to a galvanic cell, you would use the Nernst Equation, which is Ecell = Enot - RT/nF lnQ, where Q = [products]/[reactants]. If you are given all other variables, you can solve for the concentration of the anode or cathode.

Ashley Nguyen 2L

E standard cell, which is sometimes called Enot, is the standard state cell potential at state conditions, which is 25C, 1 atm. Ecell is the cell potential at non standard state condition. This value can be found by using the Nernst Equation.

Ashley Nguyen 2L

To find anode concentration, you should use the Nernst Equation, which is E = Enot - RT/nF lnQ, where Q = [products]/[reactants].

Ashley Nguyen 2L

A concentration cell has the same compound as both anode and cathode. This makes the Enot equal to zero. This reaction is driven by the difference in concentrations of both the anode and cathode, with the anode being the side with the lower concentration

Ashley Nguyen 2L

The term voltage refers to the flow of electrons. If voltage is moving from left to right, then electrons is flowing from right to left. Because electricity refers to the presence and flow of electrons, they can be used interchangeably.

Ashley Nguyen 2L

deltaG = -nFE, so if E is positive, deltaG would be negative, showing that the reaction is spontaneous. If E is negative, then deltaG is negative, showing that the reaction is not spontaneous.

Ashley Nguyen 2L

Some common salts used in a salt bridge are sodium chloride, potassium chloride, and potassium nitrate. The electrolyte chosen must easily dissociate and not react with any of the chemicals in the cell.

Ashley Nguyen 2L

He will most likely give us a paper of the standard cell potentials.

Ashley Nguyen 2L

It shouldn't matter what order you write Fe2+ and Fe3+ in because they are in the same phase.

Ashley Nguyen 2L

Generally, H has a charge of +1. This is true when it acts as a cation or when it is bound to a nonmetal. H will have a charge of -1 only when it is bonded to a cation/metal.

Ashley Nguyen 2L

When solving the half reaction for O3 -> O2, both sides must be balanced by using H2O and H+. This would make the equation O3 + 2H+ -> O2 + H2O, but now the charges on each side are not balanced. So, you would add 2e- on the left side to make the charges of both sides equal to zero.

Ashley Nguyen 2L

The standard reaction potential is positive when the reaction is spontaneous.

Ashley Nguyen 2L

If you're using OH- to balance an equation, I'm going to assume the reaction is occurring under basic conditions. First, balance all elements except for hydrogen and oxygen. Then, add H2O to balance the oxygen on the opposing side. Then, balance the hydrogen by using H+, and then the charges by usin...

Ashley Nguyen 2L

When balancing a reaction in an acidic solution, balance the equations by using H3O+ and H2O. If in a basic solution, balance by using OH- and H2O. Everything else will remain the same.

Ashley Nguyen 2L

If ice is placed in water, the system will attempt to equilibrate with heat flow from the water to the ice. Therefore, qWater = -qIce. This can also be derived from the fact that qWater + qIce = 0, since all heat is being exchanged between the 2 objects and nothing else.

Ashley Nguyen 2L

For irreversible reactions, pressure is held constant as temperature changes, while reversible reactions show the change in both temperature and pressure. For irreversible reactions, work = - PdeltaV. For reversible, work = - nRTln (V2/V1), which represents an integral. In addition, entropyTotal = 0...

Ashley Nguyen 2L

Because work is equal to Pexternal*deltaV, in a vacuum there is no external pressure, making work = 0. The system is not doing work on the surroundings because the surroundings are not pushing back.

Ashley Nguyen 2L

DeltaH is simply q at constant temperature, so it is the same by default. At constant pressure, deltaH is for a phase change.

Ashley Nguyen 2L

Yes, an isolated system would have w = 0 and q = 0 because no work can be done on or by the system and no heat can be exchanged. This also means that deltaU would equal zero because interna energy = q + w.

Ashley Nguyen 2L

Spontaneous and favorable refers to the same thing: the reaction will occur without external energy being added.

Ashley Nguyen 2L

DeltaU = 0 when there is an isothermal expansion. Although work is used, and heat is consequently lost, heat flow from the surroundings replaces the heat lost, so temperature remains constant. If we know that deltaU = 0, and that deltaU = w + q, then q = -w. We can confirm that w is a negative value...

Ashley Nguyen 2L

Mass and moles in a problem usually refers to the same amount of a chemical because the two values can be converted into each other. When using mass, you calculate using the specific heat capacity, which gives joules per gram degree Celsius. When using moles, you calculate using molar heat capacity,...

Ashley Nguyen 2L

q = mCdeltaT should be used when temperature is changing. The delta shows that we take the final and initial temperatures into consideration, and all other variables are constant. When changing from one phase to another, the temperature does not change - just the phase. The q for the phase change ca...

Ashley Nguyen 2L

If work is done by the system, then w should be positive (system is gaining heat). If work is done on the system, then w should be negative (system is losing heat).

Ashley Nguyen 2L

Remember the equation used to calculate work: w = -P (deltaV). If volume were to decrease, then work would be positive, meaning that the surroundings did work on the system. If the volume increased, then work would be positive, meaning the system did work on the surroundings. The example Lavelle use...

Ashley Nguyen 2L

A state property is a value that does not depend on the path you take to get to a state, as long as you get to the final state. Enthalpy is a state property because this value only cares about the final and initial properties.

Ashley Nguyen 2L

I usually solve these problems by first lining up all the reactions so unnecessary reactants and products cancel out, flipping equations and multiplying by a coefficient when necessary. Keep in mind which equations you flip and change so you can also flip the sign or multiply the delta H. Then, you ...

Ashley Nguyen 2L

Heat transfer refers to q

Ashley Nguyen 2L

At least for me, I think the best way to do these problems is to draw the lewis structures to figure out which bonds are formed and broken in the duration of the reaction

Ashley Nguyen 2L

Stronger bases form weaker conjugate acids. Higher pKa shows weaker conjugate acids because pKa is the negative log of Ka, which shows how much an acid would dissociate. To rank the compounds from weakest to strongest base, rank them in order of increasing pKa.

Ashley Nguyen 2L

If the x is < 10^-3, then you can assume that the x has no effect on the denominator.

Ashley Nguyen 2L

When pressure increases, the reaction shift towards the side with less gas moles, and when pressure decreases, the reaction shifts towards the side with more gas moles. Shifts in temperatures depend if the chemical reaction is exothermic or endothermic. If endothermic and temperature increases, then...

Ashley Nguyen 2L

You know that [H3O+] = 10^-pH and [OH-] = 10^-pOH. You can get the Ka or Kb values from using the [H3O+] and [OH-] respectively.

Ashley Nguyen 2L

You should not receive a negative square root. You most likely did something wrong in the math and should check your work

Ashley Nguyen 2L

Pa is for acids and Pb is for bases. Depending on if you are solving for pH or pOH, use Pa to find pH and Pb to find pOH.

Ashley Nguyen 2L

H2O is usually not included in its liquid form because it has a concentration of 1 at all times.

Ashley Nguyen 2L

In an endothermic or exothermic reaction, you can treat heat as a reactant or product depending on the reaction. In an endothermic reaction, heat is required, so heat would be considered a reactant. In an exothermic reaction, heat is released, so it would be considered a product. If you were to incr...

Ashley Nguyen 2L

When doing an ICE table, do not include water, liquids, or solids, as these do not have concentrations.

Ashley Nguyen 2L

If the reaction is endothermic (requires heat), pretend like heat is a reactant in the equation. [ A + B + heat -> C ] From here, you can treat an increase/decrease in temperature as an increase/decrease in reactant. If temperature increases in an endothermic reaction, then the reaction will shift r...

Ashley Nguyen 2L

Solids and liquids are not included in the K calculation because K is calculated using concentrations. Solids and liquids do not have concentrations, so they cannot affect the equilibrium.

Ashley Nguyen 2L

Kc is the equilibrium constant using concentrations, while Kp is the equilibrium constant using partial pressures. Both are calculated the same way.

Ashley Nguyen 2L

D and E will remain the same. Both are equation used to find K of the reaction in the forward and reverse direction. This ratio is a fixed constant.

Ashley Nguyen 2L

Change in molar concentration is usually positive on the product side because product are being created from the reactants. This means that the reactants must have a negative change in concentration.

Ashley Nguyen 2L

K does not have any units because it is calculated using an approximation of a compound's chemical activity, which is unit-less.

Ashley Nguyen 2L

How do you determine at what point the nitrogens are too far away to bond to the same metal atom? I think it's more of a common sense thing. If the nitrogens are on complete opposite sides of the benzene ring, it would be impossible for them to bond to the same metal atom. The ideal distance is nit...

Ashley Nguyen 2L

Does anyone know what Dr. Lavelle means when he says: atom with lone pair --- spacer atom --- spacer atom --- atom with lone pair The only part i dont understand is spacer atom. What does spacer atom mean? Conceptually I see why C is the correct answer i am just unfamiliar with this terminology Spa...

Ashley Nguyen 2L

Iron is called ferrate because it is derived from its latin name ferrum. Because the periodic table refers to iron by its latin name (Fe), then we also take the latin root while naming.

Ashley Nguyen 2L

polydentate refers to the bonding of a ligand to more than one binding site of a central ion. This usually refers to lone pair donating sites on the central atom.

Ashley Nguyen 2L

a. hexacyanoferrate (II) - there are 6 cyanide groups, and 1 iron atom; iron becomes ferrate, and because the overall charge of the coordination compound is negative, it receives the -ate suffix. You can tell the iron has a +2 charge because each cyanide has a -1 charge (x6) and the overall charge i...

Ashley Nguyen 2L

The metal anion receives the -ate suffix when the coordination compound is negative overall

Ashley Nguyen 2L

a. The name should be pentamminebromidocobalt (III) sulfate. This is because there are 5 ammonia groups, 1 bromide atom, 1 cobalt with a +3 charge, and a sulfate.
b. The formula is [Cr(NH3)4(OH2)2] Br3

Ashley Nguyen 2L

ICl2- would be nonpolar because dipoles are created only from bonded electrons. The 3 lone pairs do not have a strong enough force to create a dipole in this molecule.

Ashley Nguyen 2L

I believe the best way would be to treat this molecule as a hydrocarbon chain with the nitrogen on the end. The nitrogen will most likely be double bonded to the end carbon, but be sure to check how many electrons the molecule should have and formal charges.

Ashley Nguyen 2L

Many atoms with multiple electron density regions can create linear molecules with the right number of lone pairs. AX2, AX2E2, AX2E3, and AX2E4 are all linear with lone pairs.

Ashley Nguyen 2L

Ionic bonds are normally formed between any metal and any nonmetal because of their difference in electronegativity, which allows one atom, the anion/metal, to "take" electrons away from the cation/nonmetal. Metals include both the alkali and alkali-earth metals, as well as some transition...

Ashley Nguyen 2L

N is the central atom because it is the least electronegative and because if formal charges are calculated, placing N as the central atom allows each atom to have the lowest FC. There are two sigma bonds and two pi bonds. The N-O single bond is a single sigma bond, while triple bond between N and N ...

Ashley Nguyen 2L

Although both molecules are composed of the same atoms, they have different structures which impacts the types of bonds they make. Both molecules create induced dipole-induced dipole bonds, but the strength of these forces differ because of the size of the molecules. Pentane is a smaller molecule so...

Ashley Nguyen 2L

Butanol has the strongest intermolecular bonds because of the -OH group that allows it to create hydrogen bonds between molecules. Diethyl ether has no OH group nor any strong partial positives/partial negatives, so the strongest bond it can make is a london dispersion force, which is the weakest of...

Ashley Nguyen 2L

For this problem, the choice showing dipole-dipole interactions between the molecules has the strongest attraction. In choice II, the partial positive H are nearest to the partial negative Cl, giving these molecules the strongest intermolecular interaction. In addition, you know that different molec...

Ashley Nguyen 2L

NaCl's ionic bonding is much stronger than the covalent bonds holding HCl together. Because the bond is stronger, more energy is needed to break the bond, resulting in a higher melting point.

Ashley Nguyen 2L

Dipole-dipole interactions are different than london dispersion forces. Dipole-dipole interactions occur between the partially positive charged atoms of one molecule and the partially negative charged atoms of another molecule. These partial positives occurs as a result of differences in electronega...

Ashley Nguyen 2L

Because we have not discussed shape yet, which depends heavily on electron placement, it does not matter which side the lone electron goes on.

Ashley Nguyen 2L

Dipole moments have many names, which include van der waals forces and london dispersion forces. Basically, the electron cloud around an atom can be influenced by the temporary positive attraction of another atom it is not bonded to. This temporary interaction creates a weak intermolecular bond betw...

Ashley Nguyen 2L

Formal charge is really mostly used to find the most stable resonance structure, so I would calculate it if a molecule has more than just single bonds

Ashley Nguyen 2L

No, that will not be on the midterm

Ashley Nguyen 2L

I think we should just know the portion of the EM spectrum it corresponds to. I don't think there will be any in-depth questions on it

Ashley Nguyen 2L

The noble gases are included in all trends except electronegativity and electron affinity. This is because noble gases have a full valence shell of electrons, which means that they are in their most stable state. Because of this, they would not attempt to attract any electrons from another source, r...

Ashley Nguyen 2L

Ionization increases as you go up and to the right because, as you move to the right, the atoms have more protons in their nucleus, which exhibit a greater nuclear charge. This stronger positive charge attracts electrons more heavily, which makes it difficult for an electron to be pulled away. The e...

Ashley Nguyen 2L

The best way to tell which atom has the lowest ionization energy is by memorizing the periodic trends. Ionization energy increases as you go up and to the right. This is because ionization energy is defined as the amount of energy needed to remove an electron. As you move towards the right side of t...

Ashley Nguyen 2L

I'm not sure which ones we'd need to memorize for sure, but it's best to remember atomic radius, electron affinity, ionization energy, and electronegativity. Atomic radius increases towards the bottom left. Electron affinity increases towards the top right. Ionization energy and electronegativity in...

Ashley Nguyen 2L

Question 1E-1 states: w hich of the following increase when an electron in a lithium atom undergoes a transition from the 1s-orbital to a 2p-orbital? (a) Energy of the electron. (b) Value of n. (c) Value of l. (d) Radius of the atom. Which answers would be different for a hydrogen atom and in what w...

Ashley Nguyen 2L

For ground state atoms, the ionic radii changes from bigger to smaller across a period because as the number of protons increases, the effective nuclear charge also increases, which pulls the electrons closer to the nucleus. However, anions follow a different pattern because they are bigger than the...

Ashley Nguyen 2L

You know that a d subshell corresponds to l = 2, and the ml is given by -l to l. Therefore, there are 5 values of ml: -2, -1, 0, 1, 2. You can also use the equation ml = 2l + 1 to find the value of ml.

Ashley Nguyen 2L

The energy of an electron increases when it moves up an energy level. This is because energy, in the form of a photon, can excite an electron to a higher state. Conversely, when an electron moves down an energy level, it loses energy.

Ashley Nguyen 2L

Shells are divided into subshells, which are further divided into orbitals. The principle quantum number n gives the shell, while the angular momentum number l gives the subshell. The last main quantum number, ml, which is the magnetic quantum number, gives the orbital of the electron.

Ashley Nguyen 2L

On this problem, you are given the mass and uncertainty in velocity. You can use these numbers to solve for the uncertainty in momentum using the equation p = mv. You can then use this calculated value of p in the Heisenberg Uncertainty Principle, which is defined as deltaP*deltaX >= h / (4pi). Rear...

Ashley Nguyen 2L

In the photoelectric experiment, light was acting as a particle known as a photon. Increasing the intensity of the light changed only the number of photons being used and nothing else. This is why increasing intensity did not affect the electrons being emitted. A single photon must have enough energ...

Ashley Nguyen 2L

An eV is an electron volt, so a keV is a kilo-electron volt. To convert this unit to Joules, first multiply by 1000 eV/1keV to get the number in normal eV units. Use the conversion factor 1 eV = 1.602 x 10^-19J to get joules. Once you have joules, use the equation E = (hc)/(wavelength) to receive wa...

Ashley Nguyen 2L

Yup, you're right. In the equation c= (frequency)(wavelength), frequency and wavelength are inversely proportional because their product is a constant, the speed of light. If frequency were to increase, then wavelength would have to decrease. In the next equation E = hv, energy is equal to frequency...

Ashley Nguyen 2L

Yup, that would mean the least to greatest amount of energy. In terms of wavelengths and frequencies, the photons with the least amount of energy would have the longest wavelengths/lowest frequency. The photons with the greatest amount of energy would have the shortest wavelength/highest frequency b...

Ashley Nguyen 2L

Following the EM spectrum, the photons would be ordered microwaves, visible light, ultraviolet radiation, x-rays, gamma rays from lowest to highest energy. This is because microwaves has the lowest frequency/longest wavelengths, which corresponds to lower energy. The higher the frequency/shorter the...

Ashley Nguyen 2L

The Balmer and Lyman series are grouped the way they are because of how they were discovered. The Balmer series corresponds to the emission lines emitted when a hydrogen atom returns to the energy level with principle quantum number 2. The Lyman series corresponds to the lower energy level with prin...

Ashley Nguyen 2L

How much energy is required to remove an electron from one sodium atom, given that 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. Would I just use the conversion 1 mol = 6.02x10^23 atoms to convert the w...

Ashley Nguyen 2L

If you were given the total molecular mass and the mass percentage composition of each element, you can assume that you have 100. g of the substance and convert each percentage to its respective mass (ie converting 45.6% carbon to 45.6 g of carbon). Next, you would find the moles of each element by ...

Ashley Nguyen 2L

I don't believe UV radiation is harmful to our skin because of its potential to eject electrons. Because our skin is not made of metal and we are not in a vacuum, the concept of the photoelectric effect does not apply to our skin. UV radiation is harmful to us because the rays have enough energy to ...

Ashley Nguyen 2L

To find the wavelength and frequency of the photon in this question, it is best to start from what you know. You know the energy of the photon, so the only equation we can use in this instance would be E(photon) = vh, where v is the frequency in Hertz and h is Planck's constant. Rearrange the equati...

Ashley Nguyen 2L

You are correct. Shorter wavelength/higher frequency corresponds to higher energy, while longer wavelength/lower frequency corresponds to lower energy. This is because a particle is able to complete more oscillations in a 1 second interval.

Ashley Nguyen 2L

If light is at a higher intensity, the amplitude of the wave is simply higher. The frequency and wavelength remains the same. One way you could achieve a higher intensity light is by increasing the number of photons. However, this change did not impact the photoelectric experiment because one single...

Ashley Nguyen 2L

According to the equation c = λv, where c is a constant representing the speed of light in a vacuum, λ (wavelength) and v (frequency) are indirectly proportional. If frequency were to increase, wavelength must decrease. In this question, the frequency decreases, so wavelength must therefore increase...

Ashley Nguyen 2L

How do you find the formula for magnesium sulfate heptahydrate? To find the formula for magnesium sulfate hydrate, you must know the ions that magnesium and sulfate form. Magnesium always forms Mg2+ and sulfate is (SO4)2-. Therefore, magnesium sulfate is MgSO4. Hepta- is a prefix meaning 7, so ther...

Ashley Nguyen 2L

The percentage yield is the actual yield, which is the 25.2g of hydrazine, divided by the theoretical yield, which is the maximum product that can be produced, then multiplied by 100 to obtain a percent. To find the theoretical yield, you would need to convert the grams of reactant, ammonia, to mole...

Ashley Nguyen 2L

Rounding in chemistry usually occurs at the very end of your calculations in order to prevent rounding differences from accumulating.

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