CHEMISTRY COMMUNITY

RobinFong_2B

I see that on outline 6 it doesn't indicate that we should know the integrated form of 3rd order rxns. Can we assume that we won't get tested on reactions above the 2nd order for our final?

RobinFong_2B

Half-life is non-dependent on initial concentration for first-order reactions only, all other order reactions do depend on the initial concentration.

RobinFong_2B

it means to apply the equation PV=nRT and manipulate it to fins any of the given variables provided the rest.

RobinFong_2B

the entropy of the universe is the sum of the entropy of the surroundings and system.

RobinFong_2B

a decrease in volume means an increase in pressure, thus the side of the reaction with fewer moles would be favored. Think about it as when there is less space available, the side of the reaction where less of the limited space is taken up is favored.

RobinFong_2B

delta H indicates exo/endothermic. Delta G indicates spontaniety.

RobinFong_2B

Here's a good source that covers all log properties: http://dl.uncw.edu/digilib/Mathematics/ ... gprop.html

RobinFong_2B

delta H is enthalpy. While a -H value indicates that the reaction is likely exothermic we can't be sure because it is also dependent on the sign of entropy. Taking both into account we can determine the sign of free Gibbs energy which is a better indicator of spontaneity.

RobinFong_2B

extensive properties depend on the amount of moles there are in a reaction

RobinFong_2B

there's an inverse relationship. By that logic pressure and entropy are also inversely related since volume and entropy have a direct relationship.

RobinFong_2B

Spontaneous: -G, +E, K>1, -H(in most cases)
non-spontaneous: +G, -E, K<1, +H (in most cases)

Gibbs's free energy is more telling of spontaneity than enthalpy. If you are able to calculate Gibbs free energy, do it to determine spontaneity instead of passing your answer off of the signs of H.

RobinFong_2B

Kw is the equilibrium constant of water (10^-14) where Ka*Kb=Kw

RobinFong_2B

bi denotes two molecules within the reactants vs uni which denotes 1

RobinFong_2B

It means that the reaction will favor the production of products to move towards equilibrium. Because the reaction quotient measures [P]/[R] of the reaction not in equilibrium it is telling of the direction that the reaction will move in to achieve equilibrium. Having a value less than K means that ...

RobinFong_2B

F is Faraday's constant (96485 C/mol). Note: It can be combined with other constants in other equations to create larger constants (ex: RT/F) to make calculations simpler.

RobinFong_2B

boiling point is temperature while the heat of vaporization is the enthalpy of the reaction where that specific substance change states from liquid to gas. When you divide heat of vaporization by the boiling point (Kelvins) you get entropy of vaporization.

RobinFong_2B

it's the number of transferred electrons in a redox reaction. It is dependent on the moles of the reactants/products of the balanced chemical equation.

RobinFong_2B

that would decrease entropy

RobinFong_2B

you can use either ln(K) and log(K), but you should be careful of the constants you use with each. You use 0.0592 V as (RT/F) for log and 0.2569 V for ln.

RobinFong_2B

if you are looking at a cell diagram, the anode is on the left and the cathode is on the right.

RobinFong_2B

two lines indicate the salt bridge, which separates the reactions that take place in the anode(left) and the cathode(right).

RobinFong_2B

negative delta H means the system has lost heat to its surroundings. Positive delta H means that the system has gained heat from its surrounding.

RobinFong_2B

work being done ON a system is positive. Work being done BY a system is negative.

RobinFong_2B

it would be [A]0/2k

RobinFong_2B

An equilibrium constant that is less than one indicates a reaction where the concentration of products is less than that of reactants. Thus, the reaction is favoring the reverse reaction to form reactants. The standard free Gibbs energy tells us whether or not the forward reaction is spontaneous, wh...

RobinFong_2B

volume and pressure are constant in a closed system, but a styrofoam cup has no cap, thus the system is open and you can loose your material to the system.

RobinFong_2B

yes, qrev and DH are interchangeable for this equation.

RobinFong_2B

It's the use of the equation PV=nRT, where we can solve for any one of these variables if given the rest of them. Assuming constant pressure, and temperature

RobinFong_2B

rate laws are always positive!

RobinFong_2B

I'm confused about the recent update about credit given in the chemistry community. Do our answers only receive credit if there are less than two replies for that specific post? Or do our questions need to have a minimum of two answers in order to receive credit? Please provide some clarification!

RobinFong_2B

It's a mistake in the solution manual. The minus sign should be an equal sign.

RobinFong_2B

cathodes have a positive potential, and anodes have a negative potential. So as an absolute, a positive number is larger than a negative number. Electrons move from a place of negative to positive potential.

RobinFong_2B

They shouldn't be able to generate electricity. when the potential of a cell is zero, it indicates that the battery is dead and the reaction is at equilibrium

RobinFong_2B

Hydrogen always has an oxidation number of +1. There are 4 hydrogen atoms, so as a whole the 4 atoms have a +4 oxidation number. Since the molecule is neutral, N2's oxidation number must sum with H4's to make zero. Thus it must equal -4, and the oxidation number of a singular Nitrogen atom in this m...

RobinFong_2B

neutral molecules exist in a structure where their formal charge is zero. by having a structure where oxygen is in the middle a formal charge in which the octet rule is satisfied is difficult to achieve.

RobinFong_2B

What role does C(gr) play in a galvanic cell? I know Pt(s) is an inert electrode. Does graphite carbon do the same thing? When would we need to include it in our call diagram?

RobinFong_2B

For problem 6L.7 in the text book they give this cell diagram: Pt(s)|H2(g)|H+(aq)||Cl-(aq)|Cl2(g)|Pt(s) for the chemical equation: H2(g)+Cl2(g)--> 2HCl(aq) The answer I got reversed the order on the cathode side, where CL2 and Cl- switch places. Is the order of the two important? and if so, why are ...

RobinFong_2B

I noticed the answers to the questions in the textbook that ask for the equations of K for a chemical equation in equilibrium give their answers using the partial pressure of products and reactants. Should we assume that when asked for K, they are referring to K sub p and not K sub c, where we would...

RobinFong_2B

Where do we find the answers to the textbook practice problems?

RobinFong_2B

The standard state is the measurements of an element or chemical reaction taken at 25 degrees celsius. This makes it easier for people in the science community to communicate about certain processes. Think standardized units.

RobinFong_2B

another relationship is that Ka is directly related to pH, but inversely related to pKa.

RobinFong_2B

I believe this is in reference to the fact that strong acids are completely disassociated in water. Thus, with simple stoichiometry, you can easily deduce the concentration of H3O+ and pH that forms after the reaction occurs.

RobinFong_2B

It is endothermic because a substance in a liquid state has more energy than its solid-state. The reaction requires energy(in the form of heat) in order to break its bonds. As a result, liquids are at a higher energy level and the net change in enthalpy is negative when you transition from a solid t...

RobinFong_2B

If the reactant quotient(Q) is less than the equilibrium constant (K), then the current ratio of products to reactants is less than what is expected when the reaction reached equilibrium. Thus, the chemical equation will favor the forward direction to increase the concentration of products in order ...

RobinFong_2B

A characteristic of a strong acid is that it completely disassociates in water. So the pH can easily be calculated using stoichemetry.

RobinFong_2B

For a state function, we are only concerned with the variable's current state. So in order to find the value of the current state we have to add or subtract the intermediate steps. A characteristic of a state property is that they can be added or subtracted.

RobinFong_2B

There's a list of specific strong acids and bases that should be memorized. Here is a Quizlet based off that information in 14A: https://quizlet.com/_apwxsm?x=1jqt&i=139vj2

RobinFong_2B

I assume you were given a chemical equation for this problem?

In that case, I would set up an icebox to find the concentration of H+ or H3O+ ions and then take the negative log of that value to determine the pH. Hope that helps.

RobinFong_2B

Likely not, a change in two variables often complicates a problem and it's hard to deduce an outcome.

RobinFong_2B

Endothermic! sublimation requires heat to break its bonds and convert to a gas, thus it has a positive change in delta H.

RobinFong_2B

From lecture on Jan 21, Dr. Lavelle gave us 2 methods to calculate the net delta H for the formation of nitrogen dioxide from the elements in their natural state. Will there ever be a case where Hess' method will not work, and we must use the bond enthalpy method, and vice versa? I think the use of...

RobinFong_2B

At the end of lecture, Dr. Lavelle asked the question, "Why does steam cause severe burns?" I understand that the answer has to do with the heating curve for water, but I was wondering if someone could provide me with a more solid and conceptual answer to this question. Thank you:) Steam,...

RobinFong_2B

Is there a specific reason that we assume that the temperature is 25 degrees when doing calculations and not another temperature, or is 25 degrees just an arbitrary number to choose when assuming temperature? I believe it's because it's to standardize the measurements we take for elements, but also...

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