CHEMISTRY COMMUNITY

Hannah Fiel 2H

Referring to the list of standard reduction potentials, you will find the following reduction potentials for the given elements in the reaction Fe2+(aq) + 2e– → Fe(s), standard reduction potential= –0.44 Ag+(aq) + e– → Ag(s), standard reduction potential=0.8 Use this equation to calculate the standa...

Hannah Fiel 2H

In reduction reactions, the reactant gains electrons. In oxidation reactions, the reactant loses electrons. Ex: Zn + Cu2+ -> Zn2+ + Cu It is helpful to look at the oxidation state (charge) associated with the reactants and products. In this reaction, the charge on Zn becomes more positive. This mean...

Hannah Fiel 2H

When solving for the last part of this problem, I found it helpful to isolate time in the equation before plugging in values. Starting with the first order integrated rate law: ln [A] = ln [A]0 - kt ln ([A]/[A]0) = -kt ln ([A]/[A]0)/-k = t Once you find a value for t make sure that you convert to mi...

Hannah Fiel 2H

The 0.693 comes from the half life equation: t(1/2)=0.693/k. You may have also seen the 0.693 and ln(2), but they are the same value, and 0.693 is the value used in the formula sheet.

Hannah Fiel 2H

*convert the time (in last sentence)

not concentration

Hannah Fiel 2H

I am working on part b of the textbook problem 7B.5, using the first order integrated rate law to find reactant concentration after time has passed. The time is given in hours, but converted to seconds when the calculation is carried out in the solutions. I was wondering if there is a specific unit ...

Hannah Fiel 2H

In part a of this problem, I am wondering why reactant C is independent of the rate for this reaction? How do you determine if a reactant should/should not be factored into the rate?

Hannah Fiel 2H

From my understanding a psuedo rate first order reaction is one where there are two reactants, but one's concentration is so high that changes in it are negligible. So, we consider the reaction first order. I was wondering what concentration value/range would constitute a reactant to be so large tha...

Hannah Fiel 2H

In today's lecture (3/8) we were given an example of the equation NO + CO -> NO +CO2 and given the experimentally determined rate law of k[NO2]^2. Given this, professor Lavelle explained that the proposed intermediate would be NO3. I am curious as to how intermediates are determined based on the ove...

Hannah Fiel 2H

In today's lecture (3/8), professor Lavelle mentioned the term Pseudo order rate law. I did not fully grasp what is meant by this term and how it differs from the rate laws we have been talking about up to this point.

I would appreciate if anyone can explain.

Hannah Fiel 2H

The anode is where oxidation/ the loss of electrons occurs, while the cathode is where reduction/the gain of electrons occurs. While I believe that the anode is almost always on the left and the cathode is on the right, it would be a good idea to confirm by identifying whether electrons are lost or ...

Hannah Fiel 2H

Professor Lavelle gave the example that the reaction C (diamond) -> C (graphite) with a delta G of -3kj. The negative delta G tells us that the reaction is spontaneous and therefore thermodynamically unstable. He also mentioned that the reaction is kinetically stable because there is a high activati...

Hannah Fiel 2H

I got the exact same answer and it said it was right. Are you using the special characters feature? Make sure that you are using special characters for the multiplication symbol between Fe2O3 and 3H2O.

Hannah Fiel 2H

Everything that you have put for this question is correct except for the cathode reaction. In order to balance Cl you multiply AgCl by 2 (which you have done). Because you have done this, there are now 2 moles of Ag for the reactants, so you should multiple Ag in the products by 2. Your cathode half...

Hannah Fiel 2H

I think that platinum will be the most common inert electrode used for this class and in general. However, I don't think it is the only metal that can be used as an inert electrode. I believe that carbon in the form of graphite and gold can also be used as inert electrodes.

Hannah Fiel 2H

In galvanic cell diagrams, the double lines represents a salt bridge, separating the anode and cathode. On either side of the double lines, components of the reactions that are in different phases should be separated by a single dashed line. Ex: Zn (s) | Zn2+ (aq) || Cu2+ (aq) | Cu (s) The reaction ...

Hannah Fiel 2H

For this problem, you must use the equation delta G=deltaH -T(delta S). Set delta G equal to 0 (because 0 is the the number between pos/neg & therefore will tell you the value the sign will change) and plug in all other given values to determine the temperature that would make the reaction spont...

Hannah Fiel 2H

During the lecture on 2/24, professor Lavelle mentioned that concentration cells would try to reach equilibrium by increasing the concentration of the side with a lower concentration (left in diagram) and decreasing the side with a higher concentration. I am wondering how the concentrations change? ...

Hannah Fiel 2H

You are correct in saying that the anode is on the left and the cathode is one the right of the double dashed line representing a salt bridge. Single dashes separate elements in the cell diagram that are in contact with each other/in the same side of the the cell (both in anode or both in cathode), ...

Hannah Fiel 2H

Enthalpy: Enthalpy is the heat transferred during a reaction, so it directly correlates with the pattern you identified in regards to temperature increases/decreases. With the first three options, the temperature is increased for the phase change to occur, so the enthalpy increases/is positive becau...

Hannah Fiel 2H

I think that all isothermal reactions are also reversible, and vise versa with all reversible reactions being isothermal. Isothermal reactions have a constant temperature, this constant temperature is maintained because the system is gaining heat as it is releasing it (in infinitely small doses), ke...

Hannah Fiel 2H

I am wondering why it takes a larger input of energy for vaporization (liquid to gas) to occur than fusion (solid to liquid). They are both going to a less uniform state so I would assume that the energy required to change phases would be similar. Liquids are also in a less rigid form than solids, s...

Hannah Fiel 2H

I am confused on the reasoning behind the molar heat capacities of certain molecules being a certain coefficient times R. Can anyone explain this concept to me?

Hannah Fiel 2H

I know that the enthalpy change is equal to q when there is a constant pressure and the reaction is open to the atmosphere. How do enthalpy and heat required change under different conditions such as an increase in pressure or a closed system?

Hannah Fiel 2H

Since delta U=work and delta U=q, I was wondering if heat being added to a system means that work is being done on that system. Does energy as heat have anything to do with work?

Hannah Fiel 2H

Why is the internal energy for an isothermal expansion of an ideal gas equal to 0? Is this true for non-ideal gases?

Hannah Fiel 2H

I am wondering what changes the sign of internal energy. For all three of the systems attached below, there is a positive deltaU and a net gain of internal energy despite the processes being different (endo/exothermic). Is the change in internal energy always positive?

Hannah Fiel 2H

Can anyone help me determine what I am doing wrong for this question?

I attached my work and the question below

Hannah Fiel 2H

Can anyone help me determine where I am going wrong with question 5 of the Thermochemistry/1st Law of Thermo Maximillian? I added reactions 1 and 3 after multiplying reaction 3 by 3. To get the enthalpy of the reaction I multiplied reaction 3's enthalpy by 3 and added that to the enthalpy of reactio...

Hannah Fiel 2H

I am lost on textbook problem 4A.13. I don't understand why we found the heat capacity (in the answers) when asked to find the internal energy change. Is anyone able to explain the thought process and steps behind solving this problem?

Hannah Fiel 2H

Problem 4A.5 part b of the textbook problems says that a gas expands reversibly and isothermally. What does it mean for a gas to expand reversibly? And does isothermal mean constant temperature?

Hannah Fiel 2H

4A.3 part b of the textbook problems asks if the work positive or negative with respect to the air pump that is compressed.

What makes work positive or negative?

Hannah Fiel 2H

Do the weak acids not get accounted for when we calculate the K of the equation? Or does that just apply to solids? I believe that all aqueous solutions, including weak acids/ bases are accounted for when we calculate K because they contribute to the overall concentration at equilibrium (even if th...

Hannah Fiel 2H

Emily Lam 2H wrote:Does anyone know if we have to memorize strong acids and bases or will it be provided for us?

The list of strong/weak acids and bases can be found on the class website under learning outcomes titled "List of Acids and Bases."

Hannah Fiel 2H

is the percentage protonated, ionized, dissociated, all mean the same thing and use the same formula, or are they different things? From my understanding, the percentage protonated related to bases as they are proton acceptors. I believe that ionization and dissociated are both related to acids. Th...

Hannah Fiel 2H

As Annabel mentioned, inert gases such as Helium can be added to a reaction. However, adding inert gases does not change the concentration of the reactants nor the products so the reaction stays at equilibrium. This is not the case when you change the pressure of a reaction by increasing or decreasi...

Hannah Fiel 2H

I am unclear on how to find K because I don't know how to find the concentration of CO. Any tips of finding the concentration of carbon when given grams instead of moles & determining the concentration of oxygen in CO?

I attached an image of the problem & would appreciate any help

Hannah Fiel 2H

Hello Camilla,

You were correct in omitting 2C8H18 (s) from the equilibrium constant equation. Both solids and liquids should be disregarded when calculating k, only focusing on gases.

CHEMISTRY COMMUNITY

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Re: AchieveQ9

Re: Redox Reactions

Re: Macmillan question 11

Re: textbook exercise 7B.3

Re: Units of Time used During Calculations

Units of Time used During Calculations

Textbook Problem 7A.15

Pseudo Rate Law

Determining Proposed Intermediate

Pseudo Rate Law

Re: Ions connected by a salt bridge

Thermodynamic/Kinetic (In)stability

Re: Achieve #18

Re: achieve week 7 and 8 Question #9

Re: Platinum as Electrode

Re: Galvanic Cell Line Notation

Re: Achieve week 5 and 6 Q13

Concentration Cells

Re: Which molecules do we inset into the Cell Diagrams?

Re: Achieve Homework 5/6 #2

Re: Isothermal vs reversible

Enthalpy of Physical Changes

Molar Heat Capacities (linear, nonlinear molecules etc.)

When does delta H not equal q?

The Relationship between work and heat

Internal Energy of Isothermal Expansion

Weeks 3/4 Achieve #20

Achieve Weeks 3/4 #14

Q5 Weeks 3/4 Maximillian

Textbook Problem 4A.13

Reversible Expansion

Positive/ Negative Work

Re: Acids and Bases

Re: Acids and Bases

Re: Percentage Ionization

Re: Partial pressure effect on equilibrium composition

Q: Chem Equilibrium Part 2 Audiovisual Focus Post Assessment #30

Re: Find the equilibrium constant