Search found 50 matches
- Mon Mar 08, 2021 9:56 am
- Forum: Calculating Work of Expansion
- Topic: Work and Delta V
- Replies: 20
- Views: 2580
Re: Work and Delta V
Yep, if there is no volume change, then there is no work done by the system or on the system.
- Mon Mar 08, 2021 9:52 am
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: n in ∆G = -nFE
- Replies: 80
- Views: 4218
Re: n in ∆G = -nFE
Hi!
You first need to balance the two half-reactions so that the electrons cancel out when the half-reactions are added. The coefficient on the electrons in the half-reactions after balancing is the n.
You first need to balance the two half-reactions so that the electrons cancel out when the half-reactions are added. The coefficient on the electrons in the half-reactions after balancing is the n.
- Mon Mar 08, 2021 9:47 am
- Forum: Ideal Gases
- Topic: Conditions
- Replies: 20
- Views: 1577
Re: Conditions
STP is 273.15 K and 1 atm of pressure (technically it is a little less than 1 atm, but we usually just approximate it to 1 in this class).
- Mon Mar 08, 2021 9:44 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K
- Replies: 33
- Views: 1387
Re: K
K is the generalized expression of the products over the reactants all raised to their respective stoichiometric coefficients. Kc specifies that we are using the concentration of the products and reactants in the expression for K.
- Mon Mar 08, 2021 9:42 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: What is the purpose of having a salt bridge?
- Replies: 16
- Views: 761
Re: What is the purpose of having a salt bridge?
Hi!
The purpose of the salt bridge is to transfer ions from one cell to another so that there would not be a buildup of charge in one cell, and so electrons can continue to transfer.
The purpose of the salt bridge is to transfer ions from one cell to another so that there would not be a buildup of charge in one cell, and so electrons can continue to transfer.
- Tue Mar 02, 2021 12:12 am
- Forum: Balancing Redox Reactions
- Topic: How to Determine if a Reaction is in Basic or Acidic Solution?
- Replies: 53
- Views: 3184
Re: How to Determine if a Reaction is in Basic or Acidic Solution?
I’m pretty sure they will tell us if the reaction is in acidic or basic conditions (just based on the problems so far). Like others have said above, you can also probably tell based on whether there is a strong acid or base in the reactants or products.
- Tue Mar 02, 2021 12:09 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: To Pt(s) or not to Pt(s)? - cell diagrams
- Replies: 6
- Views: 433
Re: To Pt(s) or not to Pt(s)? - cell diagrams
You only need to add Pt(s) whenever there is no solid in that half-reaction because an electrode (which is a solid metal) is required to transfer electrons. If both half-reactions do not have a solid, then you would add Pt(s) to both sides.
- Tue Mar 02, 2021 12:06 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagrams
- Replies: 7
- Views: 432
Re: Cell Diagrams
Generally, you should include everything except for electrons, H2O, and the stoichiometric coefficients. Also, as for which side Br - was included in for that problem you mentioned, they most likely took the two half reactions that make that reaction and found which side each half reaction should be...
- Tue Mar 02, 2021 12:01 am
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 19
- Views: 764
Re: Salt Bridge
A salt bridge prevents the buildup of charge (so it keeps both half cells neutral) so electrons can continue to flow.
- Mon Mar 01, 2021 11:59 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Arranging elements with best reduction ability
- Replies: 9
- Views: 561
Re: Arranging elements with best reduction ability
I believe that a more negative (or smaller) reduction potential indicates a stronger reducing agent, and so a more positive (or larger) reduction potential indicates a stronger oxidizing agent.
- Mon Feb 22, 2021 2:15 pm
- Forum: Balancing Redox Reactions
- Topic: salt bridge?
- Replies: 8
- Views: 411
Re: salt bridge?
The salt bridge allows anions to go to the anode and cations to go to the cathode so that the reaction stays neutral, which allows electrons to continue traveling as there would not be a build up of positive charge that makes the movement of electrons unfavorable.
- Mon Feb 22, 2021 2:11 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Calculating Disorder based on molecule size
- Replies: 12
- Views: 744
Re: Calculating Disorder based on molecule size
Yes, since a larger molecule would have more subatomic molecules, and so there would be a higher degeneracy and a higher entropy as well.
- Mon Feb 22, 2021 2:07 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation numbers
- Replies: 4
- Views: 295
Re: Oxidation numbers
I first write down the oxidation numbers that are typically constant for all compounds (like Oxygen with -2 except for H2O2, Hydrogen with +1 if it is paired with an anion or -1 if paired with a cation, the corresponding charge if it is a single cation or anion (like Na+ by itself would have an oxid...
- Mon Feb 22, 2021 2:00 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Standard Conditions
- Replies: 8
- Views: 429
Re: Standard Conditions
I agree with others with assuming that the temperature would be 25 degrees Celsius or 298 Kelvin. Usually, problems would indicate the temperature in some form or another, whether it is directly stating it or stating standard temperature and pressure.
- Mon Feb 22, 2021 1:44 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated Systems
- Replies: 15
- Views: 863
Re: Isolated Systems
I believe that there is no such thing as an isolated system in real life because, like the other user has said, there will always been some kind of exchange with the surroundings no matter how insulated or sealed it is.
- Tue Feb 16, 2021 10:17 am
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Residual Entropy
- Replies: 2
- Views: 239
Re: Residual Entropy
Residual entropy is the entropy left when T approaches 0 K as it is based only on the amount of ways the molecules (and the atoms in the molecules) can orientate themselves.
- Tue Feb 16, 2021 10:10 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 3
- Views: 221
Re: Delta U
Hi! U is the internal energy of a system, and so delta U is the change of the internal energy of a system. The internal energy of a system could be changed in many ways, such as energy being transferred in the form of heat or energy transferred through different types of work. delta H is the change ...
- Tue Feb 16, 2021 10:03 am
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneity of a System
- Replies: 38
- Views: 2884
Re: Spontaneity of a System
A spontaneous reaction is indicated with a negative delta G, which usually happens when delta H is negative (so exothermic) and/or delta S is positive. A spontaneous reaction is one that proceeds in the forward direction and produces products without any energy input. As for why a spontaneous reacti...
- Tue Feb 16, 2021 9:49 am
- Forum: Calculating Work of Expansion
- Topic: Work and Delta V
- Replies: 20
- Views: 2580
Re: Work and Delta V
Work does depend on delta V because the definition of work is the energy required to move an object a certain volume against a force. So, if there is no volume change, then work would be 0, which is shown by w=-Pex(delta V).
- Tue Feb 16, 2021 9:39 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: What does the d in dq mean
- Replies: 3
- Views: 369
Re: What does the d in dq mean
The d in dq indicates that there is an infinitely small change in q, and so a large number of small changes in q could be added up to get a larger change in q. dq (and d(variable) in general) are only used in integrals and they indicate which variable is changed by an infinitely small amount.
- Mon Feb 08, 2021 3:24 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: using equations
- Replies: 11
- Views: 633
Re: using equations
I tend to start a problem off with writing down the relevant information used in the problem (such as enthalpy, entropy, P, V, T, n, etc) and writing down the value given or "unknown" if it is something the problem is looking for or a relative descriptor (such as "it is larger than th...
- Mon Feb 08, 2021 3:17 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: dT versus ΔT
- Replies: 8
- Views: 816
Re: dT versus ΔT
Like the others have said above, delta T refers to larger changes in temperature, and it is used in the calculation of work for irreversible pathways. dT refers to infinitely small changes in temperature, and it is used in integrals, such as in the calculation of work for reversible pathways.
- Mon Feb 08, 2021 3:14 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy and Phase Changes
- Replies: 5
- Views: 299
Re: Entropy and Phase Changes
Liquids have much more mobility compared to solids, and they are able to reach much more places (or volume) when placed in a container of fixed volume compared to a solid. "Positions" refers to the number of spaces the system has access to or covering, which connects to degeneracy.
- Mon Feb 08, 2021 3:08 pm
- Forum: Calculating Work of Expansion
- Topic: Temperature Change for Irreversible Pathway
- Replies: 3
- Views: 181
Re: Temperature Change for Irreversible Pathway
For the volume to increase, the system must do work of expansion, and so energy is lost in the system. This energy loss corresponds to an initial decrease of temperature.
- Mon Feb 08, 2021 3:06 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed vs Isolated System
- Replies: 30
- Views: 1369
Re: Closed vs Isolated System
A closed system is sealed so no matter can be transferred into and out of the system, but it is not insulated so energy can be transferred. An isolated system is both sealed and insulated so both matter and energy can not be transferred into and out of the system. An example of a closed system is a ...
- Mon Feb 01, 2021 2:59 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Reversible Process
- Replies: 4
- Views: 142
Re: Reversible Process
I could be wrong, but I think a reversible process does more work because all of the heat from the system is converted to work because of how long the process takes. Also, the system is pushing against more pressure gradually because we are slightly decreasing the pressure for each step. Since an ir...
- Mon Feb 01, 2021 2:49 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Internal Energy and External Pressure
- Replies: 4
- Views: 177
Re: Internal Energy and External Pressure
The external pressure should be the surroundings as it is outside of the system.
- Mon Feb 01, 2021 2:48 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Irreversible vs Reversible
- Replies: 3
- Views: 179
Re: Irreversible vs Reversible
From my understanding from lecture, an irreversible pathway occurs when the system is not at equilibrium (so the internal pressure does not equal the external pressure). From lecture, it appears that irreversible pathways are usually when the internal pressure is greater than the external pressure, ...
- Mon Feb 01, 2021 2:40 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Changes in Internal Energy
- Replies: 3
- Views: 203
Re: Changes in Internal Energy
I am pretty sure he made a mistake while writing on the board (and I believe that he later fixed it). But the second equation so be right as we are deriving the equation from delta U = q p + w, and w=-P*delta V when the system is pushing against a constant external pressure like this case. So, subst...
- Mon Feb 01, 2021 2:37 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Qp = ΔH
- Replies: 6
- Views: 356
Re: Qp = ΔH
Hi! q represents heat, and the definition of delta H is the change of heat at a constant pressure, so qp would be equal to delta H.
- Mon Jan 25, 2021 2:18 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Sapling Week 3-4 #10
- Replies: 2
- Views: 151
Re: Sapling Week 3-4 #10
Since an ice cube with a mass of 51.2 g at 0.0 ∘C is added to liquid water, the ice cube has to melt first. Also, no energy is transferred to or gained from the surroundings. Therefore, there is this relationship: heat required to melt ice cube + heat required to raise the melted ice cube to final t...
- Mon Jan 25, 2021 2:04 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Exothermic rxn
- Replies: 9
- Views: 398
Re: Exothermic rxn
I believe that he was referring to the change in heat of the surroundings. Since the change in heat of the system + change in heat of the surroundings =0, if the reaction is exothermic, and the change in heat of the system is negative as a result, then the change in heat of the surroundings should b...
- Mon Jan 25, 2021 2:01 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Molar heat Capacity
- Replies: 3
- Views: 175
Re: Molar heat Capacity
I believe that a change in Kelvin is the same value as the change in Celsius because Kelvin is just Celsius +273.15, and so we can use them interchangeably.
- Mon Jan 25, 2021 1:51 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpy of Formation
- Replies: 10
- Views: 467
Re: Standard Enthalpy of Formation
We will most likely be given the values in the problem or through a chart.
- Mon Jan 25, 2021 1:47 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Catalysts and equilibrium
- Replies: 4
- Views: 100
Re: Catalysts and equilibrium
Nope, catalysts only speed up the forward and backward reaction to the same extent, so the equilibrium would not be affected.
- Tue Jan 19, 2021 11:30 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Approximately x
- Replies: 18
- Views: 696
Re: Approximately x
We can approximate that x is small whenever the Ka < approximately 10 -3 . Professor Lavelle said that to be safe, whenever Ka < 10 -4 , you can use the approximation. You can test to see if the approximation is valid by seeing if (x/initial concentration)*100 < 5%. I don't think that approximating ...
- Tue Jan 19, 2021 11:25 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: State indications in Chemical Equations
- Replies: 4
- Views: 179
Re: State indications in Chemical Equations
Yes, the chemical reactions should have the states labeled, or the problem should classify the states in a way so that you could create the correct equilibrium expression. (s) and (l) do indicate pure solids and liquids (or solvents) and are not included in the equilibrium expression.
- Tue Jan 19, 2021 11:16 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5.35 PART A
- Replies: 1
- Views: 127
Re: 5.35 PART A
I found the coefficients for A, B, C from calculating the difference between the final and initial partial pressures of A, B, C; since the change (in x) for each of them are multiplied by the respective coefficients. B goes from about 0 to 5, C goes from about 0 to 10, and A goes from about 28 to 18...
- Tue Jan 19, 2021 11:10 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook #6D.3
- Replies: 3
- Views: 381
Re: Textbook #6D.3
For (a), you could create an ice table with the initial concentrations and setting the change as -x, +x, +x. You can calculate the [H 3 O - ] by knowing that pH=-log[H 3 O - ]. You can input that as the equilibrium concentration for [H 3 O - ] in the ice table, and calculate the other equilibrium va...
- Tue Jan 19, 2021 11:05 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Determining which is +x or -x in ICE chart
- Replies: 3
- Views: 1502
Re: Determining which is +x or -x in ICE chart
Hi! Usually, in an ice table, the side that is being used in the reaction (therefore their concentrations/partial pressures are decreasing) would have a -x, and the the side that is being formed would have a +x. Usually, the reactants side would be -x and the products side would be +x, but in the ca...
- Mon Jan 11, 2021 1:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 5h #3
- Replies: 5
- Views: 267
Re: Textbook Problem 5h #3
The first step would be finding equations in Table 5.G2 that would result in the equation once added together. A good way to pick out equations is to see whether the equations share reactants or products with the desired equation. The two equations would be: H2(g)+Cl2(g)⇌2HCl(g) and 2BrCl(g)⇌Br2(g)+...
- Mon Jan 11, 2021 1:29 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding Helium
- Replies: 10
- Views: 936
Re: Adding Helium
Adding Helium (and any other inert gas) into a container would not change the partial pressures of any of the reactants or products in the reaction. Since the partial pressures of the reactants or products are not changed, the volume (and therefore the concentration) of them would also not change (d...
- Mon Jan 11, 2021 1:26 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ATP Hydrolysis and Osmotic Pressure
- Replies: 3
- Views: 250
Re: ATP Hydrolysis and Osmotic Pressure
I am not completely sure about osmotic pressure, but there were a couple of questions about ATP hydrolysis in the modules (I think it was the post assessment for part 4, questions 16 and 17). Question 17 was this: Determine the shift in equilibrium, if any, which will occur for the following reactio...
- Mon Jan 11, 2021 1:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Cubic Equations
- Replies: 6
- Views: 268
Re: Cubic Equations
You can omit the +x or -x if K is any number less than 10-3 since that indicates that x is very small and a constant plus or minus a very small number is basically just that constant.
- Mon Jan 11, 2021 12:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Sampling hw #2
- Replies: 6
- Views: 532
Re: Sampling hw #2
The explanations above are setting the change in concentration of O 2 equal to x. Since the reactant SO 3 has a stoichiometric coefficient of 2, while O 2 has a stoichiometric coefficient of 1, the change in concentration of SO 3 would be -2x (it is negative because SO 3 is a reactant and so it woul...
- Mon Jan 04, 2021 2:48 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Module Part 2 question #29
- Replies: 2
- Views: 127
Re: Module Part 2 question #29
The initial concentration of the reactant is 1.84 * 10 -4 mol divided by 1 liter, so 1.84 * 10 -4 . The initial concentration of the products are both 0. The problem states that at equilibrium, only 18.3 % of the BrCl gas remains. So, the equilibrium concentration of the reactant is 0.183* 1.84 * 10...
- Mon Jan 04, 2021 2:32 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Chemical equ. part 4 post assess. #16
- Replies: 3
- Views: 184
Re: Chemical equ. part 4 post assess. #16
Yep, the forward reaction is exothermic! Since the forward reaction is exothermic, the reverse reaction would be endothermic, so it would require heat. So, when the temperature increases, the system would want to use up the additional heat, and so the reverse reaction (reactant formation) would be f...
- Mon Jan 04, 2021 2:23 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Post Module 1A #26
- Replies: 2
- Views: 166
Re: Post Module 1A #26
I got: One number that gives us information about the relative concentrations of reactant and product. I think since we calculate equilibrium constants as the concentrations at equilibrium of products over the concentrations at equilibrium of reactants all raised to the power of their stoichiometric...
- Mon Jan 04, 2021 1:01 pm
- Forum: Ideal Gases
- Topic: Converting to Concentration and Pressure Values
- Replies: 7
- Views: 575
Re: Converting to Concentration and Pressure Values
Also to add on, another case in which we use this conversion is when the reaction contains both aqueous solutions and gases, and the given information was partial pressures of the gases and concentrations of the aqueous solutions. We would then need to convert those partial pressures into concentrat...
- Mon Jan 04, 2021 12:40 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pure Substance [ENDORSED]
- Replies: 7
- Views: 304
Re: Pure Substance [ENDORSED]
A general definition of a pure substance is a substance consisting of only one kind of particles/material and has a fixed or constant structure. The particles could be an element (so Cu is a pure substance) or it could be a molecule. For example, H 2 O (l) would be a pure substance since it only con...