CHEMISTRY COMMUNITY

kevinolvera1j

Thermodynamics typically deals with state functions whereas kinetics deals with different pathways that control the speed of the reaction. This especially comes into play when dealing with activation energies

kevinolvera1j

k=A*e^-Ea/RT This formula helps determine the temperature dependence of reaction rates. k is the reaction rate of the reaction. A is a pre-exponential factor and has to do with the collision of the molecule (and if it is properly oriented when it collides in order to react) Ea is the activation ene...

kevinolvera1j

Is the mailroom open on saturdays?

kevinolvera1j

If you need a value for an letter that is in the law, you can almost always use the law

kevinolvera1j

If the second order rate is integrated, you end up with the second order rate law using a little calculus and algebra. The +C usually associated with an indefinite integral is represented in the integrated rate law by the initial concentration.

kevinolvera1j

ATP happens to be a very unstable molecule due to its phosphate groups being next to each other (these phosphates all have negative charges) Thus when hydrolysis occurs, the products are at a lower energy state because they are more stable apart than together.

kevinolvera1j

You should probably know that collisions need to have the appropriate amount of energy to break a bond and also be correctly oriented in order for a new molecule to form.

kevinolvera1j

Using a fraction is useful if you only want the product to have 1 mol in your equations.

kevinolvera1j

Only pay attention to gases because they can be compressed.

kevinolvera1j

How are the Gibbs free energy equations used in biology?

kevinolvera1j

How can you identify the pure form of an element?

kevinolvera1j

delta U is change in internal energy whereas delta H is change in enthalpy.

kevinolvera1j

You can use it when you can assume that delta H and delta S are the same at both temps.

kevinolvera1j

A closed system means that the system is closed off from exchanging mass with its surroundings but it can exchange energy. An isolated system cannot exchange either. Energy can be introduced into a closed system either through heat or work (increasing pressure).

kevinolvera1j

I think since B had the least amount of water, it was able to heat up the most since it didn't have to heat a larger amount of water (which has a high heat capacity)

kevinolvera1j

Are there any real world applications of the Nernst Equation not mentioned in class?

kevinolvera1j

What impact does the mass of an electrode have on the cell potential?

kevinolvera1j

Selena Yu 1H wrote:No, not all zero order reactions is dependent on a catalyst. A zero order reaction could also occur with an enzyme or a surface. It's just that most commonly you would find a catalyst with a zero order reaction.

Aren't enzymes just biological catalysts?

kevinolvera1j

Does the size of the reactant influence the rate? I.E. is a bigger molecule consumed at a faster rate than say a hydrogen atom?

kevinolvera1j

Are all zero order reactions dependent on a catalyst?

kevinolvera1j

How slow does the slowest step need to be in order to be considered the slowest step? In other words is there a real time value?

kevinolvera1j

Is it possible to determine a rate law from a tangent line or a secant line of a graph of time in seconds vs concentrations?

kevinolvera1j

Congrats!

kevinolvera1j

How can you predict if a metal will dissolve in solution? Is it solely dependent on potential?

kevinolvera1j

At equilibrium, delta g is zero, so that means we can use algebra to move it to the other side.

kevinolvera1j

When can we assume that delta entropy would be the same for different temperatures. Do the temperatures have to be close together?

kevinolvera1j

For ideal gases, Cp = Cv + R. The actual value of Cv will differ depending on whether it is monoatomic, linear (diatomic), and nonlinear.

kevinolvera1j

What keywords will be given to indicate that the a system has no external pressure acting on it such as in a vacuum?

kevinolvera1j

This law is applied to isolated systems, but since the universe is basically an isolated system, it applies to the whole universe as well.

kevinolvera1j

∆S for the products and reactants can be ignored because the function: ∆Sºrxn=∑Sºm(products)-∑Sºm(reactants) is only dependent on the actual values of the molar entropies not changes in the molar entropies.

kevinolvera1j

905289082 wrote:When calculating Gibbs free energy, do you use the same method as you would for Hess's law?

The method shown in Hess's Law can really be extrapolated to all state functions.

kevinolvera1j

If a problem explicitly tells you the reaction enthalpies you'll probably use method 1 to find net rxn enthalpy. If you have a table of bond enthalpies you'll probably use method 2. If you have standard reaction enthalpies you'll use method 2 or 3. You might even use some sort of combination of thes...

kevinolvera1j

certain key phrases give away that a system is under constant pressure such as "open beaker". This is because you can assume that an open beaker has the external pressure of the atmosphere as a constant acting on it.

kevinolvera1j

You can assume all bonds are broken and reformed from the reactants to the products stage to be on the safe side since they cancel out if you do the calculations right. However if you know which bonds are broken and formed, it can save you some time and effort when doing your calculations.

kevinolvera1j

delta H corresponds to gases more because solids and liquids do not change a significant enough amount in volume.

kevinolvera1j

mass is used directly for specific heat capacities and can be used indirectly for molar heat capacities

kevinolvera1j

Steam is worse than water even at the same temperature when coming into contact with your skin. This is because the steam has much higher enthalpy than the water, even if they are at the same temperature. Once the steam comes into contact with your skin, it condenses and this phase change releases m...

kevinolvera1j

If you're trying to incorporate a phase change into your calculation, you must take into which phase change it is. The increase in enthalpy needed to melt ice, is different from the increase in enthalpy needed to boil water. Once you know what kind of phase change you're dealing with, include it in ...

kevinolvera1j

Because Enthalpy is a state function, only the state matters. In other words, what matters is the state, not the way that those states were obtained or the path that led them there. This is what allows enthalpy to be additive.

kevinolvera1j

Why isn't heat a state function but enthalpy is?

kevinolvera1j

since phase changes can be either exothermic or endothermic, they should be taken into account when calculating changes in enthalpy.

kevinolvera1j

To calculate pOH it is simply =-log[OH-] , and to find pH it is -log[H+] or -log[H30+]. pOH is used to calculate the strength of bases, while pH is used to calculate the strength of acids. To find one if the other is given the equation is pH+pOH=14.

kevinolvera1j

The 5% rule is sort of like checking your work. If you approximated by ignoring x, if the percent ionization was less than 5%, then the approximation was fine.

kevinolvera1j

If you are unsure about the cutoff for ignoring X, you can generally ignore if K is less than 10^-3 but you can always ignore if less than 10^-5.

kevinolvera1j

If a reaction is exothermic, increasing the temperature will shift the reaction towards the reactants. If a reaction is endothermic, increasing the temperature will shift the reaction towards the products. Decreasing the temperature will shift the reaction towards exothermic products.

kevinolvera1j

If a reaction is exothermic, it releases energy. If a reaction is endothermic, it absorbs energy.

kevinolvera1j

Changing the concentrations does not change the K value. However, in the short term it will change the value of Q. Adding more products will make the value of Q larger and if Q>K then the system will favor the formation of reactants and vice versa.

kevinolvera1j

Its useful to predict the direction of a reaction since you can find Q even if the system is not at equilibrium. If K is known, and you can measure Q, then you determine which side a reaction will favor until it reaches equilibrium. If Q<K, then the reaction will favor products until K is reached. I...

kevinolvera1j

A change to concentrations does not change the equilibrium constant. That is why K remains the same even when concentrations increase or decrease. What should be noted is that K is only for reactions at equilibrium, what that means is that if you add or take away products or reactants and therefore ...

kevinolvera1j

At equilibrium, the rate of product formation and the rate of reactant formation cancel out but do not necessarily stop. This is what is meant by the saying "all chemical equilibria are dynamic" . K is a ratio of activity that is why pressure and concentration can both be used.

kevinolvera1j

For the most part, noble gases conform to the ideal gas law but the law is an approximation so make sure to keep that in mind when using it for all gases.

kevinolvera1j

Find the pH of the first value, then subtract it from the second pH value. To find the second pH value simply multiply the first concentration by (V1/V2) inside the -log.

kevinolvera1j

for a given period, the strength of an acid (specifically of an element only bonded to hydrogen) increases as you go from left to right e.g. nitrogen to oxygen to fluorine. As you go down a group, the strength of an acid increases e.g. the halogens. HI>HBr>HCl>HF

kevinolvera1j

Arsenic forms salts with both acids and bases and that contributes to its amphoteric properties.

kevinolvera1j

Why is acetic acid weaker than formic acid?

kevinolvera1j

For part b, is there a formula that tells us we can plug in the (200 x 0.025)/250 to the -log, or are we just doing the conversion to molarity using M1V1=M2V2 inside the pH=-log[H3O+] formula? I used the method of (200 x 0.025)/250 in the -log and received the correct answer. This is functionally t...

kevinolvera1j

Water is amphoteric meaning it can react as an acid or base. While acting as a base it accepts a proton from an acid and becomes a hydronium ion. While acting as an acid, it donates a proton and then becomes a hydroxide ion.

kevinolvera1j

A Lewis acid is defined as accepting an electron pair while a bronsted acid is defined as donating a proton. A lewis base is defined as donating an electron pair while a bronsted base is deifned as accepting a proton. Note that in water, the "proton" defers to a hydronium ion such as in th...

kevinolvera1j

Sidenote: conjugate acids/bases will generally be weaker than their original, strong corresponding acids/bases

kevinolvera1j

Arrhenius is a little more specified towards aqueous solutions, which is why the bronsted definition is used more generally.

kevinolvera1j

typically, a polydentate will only a polyatomic sepcies since a single atom or ion would be too small to take more than one "bite"

kevinolvera1j

Only b can form a chelating compound because only there are the NH2 groups close enough to bind to the same atom

kevinolvera1j

coordination number is determined by the number of bonds to the metal atom

kevinolvera1j

Transition are also favored for coordination compounds because they often appear as cations.

kevinolvera1j

oxidation state is more related to the cation before it bonded whereas formal charge is determined in bonds.

kevinolvera1j

IIRC he said something about naming the ligands alphabetically but ignoring the greek prefixes

kevinolvera1j

On the periodic table, the further you go down and to the left, the larger the size of the atom. In terms of periods, size decreases from left to right. In terms of groups, size increases as you go down.

kevinolvera1j

In the typical example of xenon tetrafluoride, Xenon has 4 bonds and two lone pairs. This is possible since xenon is a large atom with valence electrons far away from its nucleus (relative to the noble gases that precede it) and fluorine is electronegative enough to pull away Xenons valence electron...

kevinolvera1j

IIRC Oxygen is the second most electronegative element, second only to Fluorine. When both of these elements fill their valence they have the very stable configuration of neon. While Chlorine is closer to filling its octet than oxygen is, its valence electrons are also farther from its nucleus than ...

kevinolvera1j

All single covalent bonds are sigma bonds. Double bonds include one sigma and one pi bond. Triple bonds include one sigma bond and two pi bonds.

kevinolvera1j

Put simply, the shorter a bond is, the stronger it is, and vice versa. To understand why this happens you need to consider the electron clouds of atoms. If the electron clouds of two atoms overlap, the bond will be stronger and also shorter. More overlapping is associated with stronger bonds and sho...

kevinolvera1j

Can you identify a dipole moment by analyzing its Lewis structure and formal charge or must you also consider electronegativity

kevinolvera1j

You should know the range in nm for visible light (700-400) and also the colors associated with each end of the spectrum (red for values closer to 700nm and violet for values closer to 400nm). As for the other ranges on the electromagnetic spectrum, you should generally know the order of EM radiatio...

kevinolvera1j

For a value like "32+-0.25 meters" you multiply the +- value by two to represent the total range in uncertainty of the value. The same logic applies if you are given the radius as a possible range of position for an electron to occupy. Since you want to represent the total range of uncerta...

kevinolvera1j

The speed of light equation can only be used for Electromagnetic radiation since that equation, c=vλ is based on the propagation wave speed formula for values specific to light. The De Broglie equation is used for particles with momentum which means it is used for particles with mass, e.g. electrons...

kevinolvera1j

E=hv can only be used for Electromagnetic radiation (light). To find the energy for other particles, use the kinetic energy equation: KE=(1/2)mv^2 since other particles have mass. If you want to find the wavelength for light, use λ=c/v; for particles with mass use the De Broglie equation: λ=h/p

kevinolvera1j

Neutrons do have diffraction patterns; the De Broglie equation can be used for any object with momentum but observable wavelengths are only really present when a particle has very small mass such as electrons, neutrons, and protons. Objects on the scale of paperclips and cars have masses so great th...

kevinolvera1j

nice joke,
Helium Helium Helium

kevinolvera1j

Does being isoelectronic mean having the same number of electrons or having the same electron configuration?

kevinolvera1j

If a speed is given such as 58 +-3 m/s is stated as the speed for a particle, does 3 need to always be multiplied by 2 in order to find the indeterminacy of a delta?

kevinolvera1j

When dealing with frequency, the unit needed for equations is Hz(s^-1), also the name of the greek letter is nu, not "v" since that would be confused too easily with velocity

kevinolvera1j

Is there an easy way to identify which volumes and molarities are first and second, or is it just a matter of reading the question very carefully?

kevinolvera1j

is the limit of valence electrons the same for all these 3rd period nonmetals or does it vary atom by atom?

kevinolvera1j

So this means that this trend would also apply to silver as it applies to copper?

kevinolvera1j

Is it possible to find the length of a bond based on its strength or vice versa?

kevinolvera1j

Is there a periodic trend for polarizing power?

kevinolvera1j

Why are the p-block nonmetals in the 3rd period exceptions to the octet rule but the p-block nonmetals in the 2nd period are not?

kevinolvera1j

Can the equation for formal charge be rewritten as Valence electrons - (dots + lines)= formal charge?

kevinolvera1j

How can spin be visualized when thinking of electrons as waves and particles?

kevinolvera1j

Using E=hv to find the frequency?

Nah bro, just Einstein checking your vibes

kevinolvera1j

The video modules on the Chem 14A website are excellent resource for initially learning, but to solidify information for long-term recall, forming a study group to do practice problems/tests is a really solid strategy.

kevinolvera1j

Since h bar is equal to (h/2π) it's very useful as shorthand where this value is used often like in Heisenberg indeterminacy equation and the Schrodinger equation. In the Heisenberg equation, the (h-bar/2) is equal to (h/4π) in case you come across the equation using h-bar.

kevinolvera1j

Understanding the equation at conceptual level is important but understanding the finer details of the equation is not as important for this level of chemistry

kevinolvera1j

When thinking about the energy of light, it's more useful to think about light as photons instead of waves. Intensity in terms of photons just refers to the amount of photons present. A higher intensity means more photons. The equations relating to the energy of light, E=hv, is specifically for one ...

kevinolvera1j

the speed of light, 3.0x10^8 m/s, remains the same for all EM radiation no matter the frequency or wavelength.

kevinolvera1j

The rydberg constant is 3.29x10^15 hz when solving for frequency while in other equations it appears as 1.097x10^-7m in other equations. It's important to use the right version of the constant depending on what you are solving for.

kevinolvera1j

When showing work it's important to include the right units in your work.

kevinolvera1j

Test 1 and 2 are both 50 points each and both have 50 minute time limits.

kevinolvera1j

When dealing with Electromagnetic radiation (light) its useful to use the light equations : E=hν and c=λν, but keep in mind that these equations are specific to EM radiation. This is where De broglie's equation comes into play when dealing with the other particles (that have mass). De broglie's equa...

kevinolvera1j

You will most likely need to understand the relationship between each wavelength range (radio, microwave, infrared, visible light, UV, X-ray, and gamma) and their respective frequencies as it relates to the energy of each segment of the spectrum.

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