Search found 50 matches

by 205291012
Sat Mar 14, 2020 4:01 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: kinetics
Replies: 9
Views: 85

Re: kinetics

you would probably need a catalyst to lower the activation energy. I think it wouldn't occur spontaneously due to the high activation energy.
by 205291012
Sat Mar 14, 2020 3:59 pm
Forum: Balancing Redox Reactions
Topic: OH vs H
Replies: 12
Views: 115

Re: OH vs H

I would stick to balancing basic solutions with OH- and acidic with H+.
by 205291012
Sat Mar 14, 2020 3:56 pm
Forum: General Rate Laws
Topic: rate laws
Replies: 8
Views: 105

Re: rate laws

yes, the rate depends on the slow step since it is the limiting step
by 205291012
Sat Mar 14, 2020 2:56 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 8
Views: 87

Re: Concentration Cells

in a concentration cell, the standard potential energy is 0 and the potential energy is very low voltage. the whole reaction is driven entirely by a change in concentration gradient. thus the reaction proceeds because there is a tendency to move from high concentration to low concentration
by 205291012
Sat Mar 14, 2020 2:55 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Activation Energies
Replies: 4
Views: 34

Re: Activation Energies

No activation energies are not always constant. If you add a catalyst, it tends to lower the activation energy and thus the reaction can progress faster
by 205291012
Tue Mar 03, 2020 11:05 pm
Forum: Balancing Redox Reactions
Topic: Balancing half reactions in acidic conditions
Replies: 8
Views: 63

Re: Balancing half reactions in acidic conditions

Use H2O to balance the Os first and then use H+ to balance the H. if you used H30+ to balance the H then you would once again add Os to the other side.
by 205291012
Tue Mar 03, 2020 11:02 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Reducing Power
Replies: 3
Views: 42

Re: Reducing Power

Reducing power means the ability to give away electrons. If it has a high tendency to give away electrons then it is a good reducing agent and therefore, likely to be oxidized itself.
by 205291012
Tue Mar 03, 2020 11:01 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidizing Power
Replies: 3
Views: 28

Re: Oxidizing Power

Yes, if something has oxidizing power then that is the same as saying it is a strong oxidizing agent.
Oxidizing agent is the same as what is being reduced.
If it is good at being reduced then it would have a high or more positive reduction potential.
by 205291012
Tue Mar 03, 2020 10:59 pm
Forum: Balancing Redox Reactions
Topic: Number of Electrons Being Transferred
Replies: 5
Views: 42

Re: Number of Electrons Being Transferred

Once you are done balancing all the elements on both sides. calculate net charge on both sides and then determine which side would need electrons such that the netcharge on both sides is equal. One way to make sure you're writing it correctly is to check if there you added electrons on the LEFT for ...
by 205291012
Tue Mar 03, 2020 10:56 pm
Forum: Balancing Redox Reactions
Topic: MnO4-
Replies: 5
Views: 41

Re: MnO4-

MnO4-

Let the charge of Mn = x.
Charge of O= -2
Overall charge = -1

x + (-2*4) = -1
x - 8 = 1
x = -1+8
x = +7
by 205291012
Tue Mar 03, 2020 10:55 pm
Forum: Balancing Redox Reactions
Topic: adding correct charge
Replies: 4
Views: 27

Re: adding correct charge

Adding electrons should be the last step after you have balanced all the elements, H, O. Then look at net charge on both sides and you can add the electrons accordingly.
by 205291012
Tue Mar 03, 2020 10:52 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells
Replies: 3
Views: 32

Re: Galvanic cells

Oxidation will be at the anode and reduction at the cathode. The sides could be switched but typically we keep anodes on the left and cathodes on the right. When there is a gain of electrons or the oxidation number decreases then it is reduction. When there is a loss of electrons or an increase in o...
by 205291012
Tue Mar 03, 2020 10:50 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6L.7
Replies: 2
Views: 33

Re: 6L.7

Use the half reaction from the appendix that has both your species present in it.
by 205291012
Tue Mar 03, 2020 10:49 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum and Granite
Replies: 4
Views: 39

Re: Platinum and Granite

Use platinum since it is more common. And use it when there are no conducting solids or if the species reduced and oxidized are in the same solution.
by 205291012
Tue Mar 03, 2020 10:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Including Inert Electrodes
Replies: 2
Views: 31

Re: Including Inert Electrodes

Use inert electrodes when both the oxidized and reduced species are in the same solution. Also, use inert electrode when there are gas/ion reactions like in 6L.5 (c).
by 205291012
Tue Mar 03, 2020 10:36 pm
Forum: Balancing Redox Reactions
Topic: 6L.9 part a
Replies: 2
Views: 32

Re: 6L.9 part a

Find the half reactions in the appendix and then compare the cell potential values that are given. Whichever equation has a higher E naught value will be reduced and thus the other will be oxidized.
by 205291012
Tue Mar 03, 2020 10:34 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Determining Anode and Cathode
Replies: 4
Views: 51

Re: Determining Anode and Cathode

You need to look for the reduction half reaction in the appendix at the back of the textbook. Look for the 2 equations that have both your species. The one with a more positive reduction potential value will be more likely to be reduced. So the other equation will be oxidized and you can flip it.
by 205291012
Tue Mar 03, 2020 10:30 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell diagram order of phases
Replies: 6
Views: 53

Re: cell diagram order of phases

Keep solids towards the ends in general. I'm not sure if you can switch Cl2(g) and Cl2(aq) but to be safe, I wouldn't. It also makes since since the right side is reduction so it is going from Cl2 (g) (oxidation number 0) to Cl2 (aq) (Oxidation number -1).
by 205291012
Tue Mar 03, 2020 10:30 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: E cell
Replies: 2
Views: 43

Re: E cell

Yes, that is correct! both are good methods but the one where you flip the value for oxidation usually makes more sense conceptually.
by 205291012
Tue Mar 03, 2020 10:29 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Potentials
Replies: 2
Views: 24

Re: Standard Potentials

You need to find the species from your redox reaction in the appendix 2B and use those potential values.
by 205291012
Tue Mar 03, 2020 10:28 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Metal as solute
Replies: 2
Views: 61

Re: Metal as solute

If a metal has a more negative reduction potential then it is more likely to be oxidized. therefore, it will be more likely to dissolve compared to the one that has a more positive reduction potential.
by 205291012
Tue Mar 03, 2020 10:27 pm
Forum: Van't Hoff Equation
Topic: derivation?
Replies: 3
Views: 80

Re: derivation?

I think you should probably know the derivations of equations that aren't on the formula sheet. Also know the derivations if the objectives include knowing the derivation.
by 205291012
Tue Mar 03, 2020 10:26 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: G=-nFE equation [ENDORSED]
Replies: 4
Views: 148

Re: G=-nFE equation [ENDORSED]

Standard will have that naught or little circle next to G and E. It means standard conditions (solutions are 1M, gases are 1bar or 1atm, solids and liquids are in pure form, temp is 25 degrees celsius). If it isn't standard then there is no circle.
by 205291012
Tue Mar 03, 2020 10:23 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Writing cell diagrams
Replies: 2
Views: 22

Re: Writing cell diagrams

That's correct, you don't need the stoichiometric coefficients when writing cell diagrams.
by 205291012
Tue Mar 03, 2020 10:22 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: change in gibbs free energy
Replies: 4
Views: 65

Re: change in gibbs free energy

I think delta G is probably positive since the process is not spontaneous. You have to input energy in the form of photons for the reaction to take place. Therefore, there isn't free energy available to do work. I'm not sure though.
by 205291012
Thu Feb 06, 2020 10:15 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Isolated vs Closed [ENDORSED]
Replies: 34
Views: 414

Re: Isolated vs Closed [ENDORSED]

In an isolated system, the system cannot exchange matter or energy with the surroundings. In a closed system, the system has a fixed amount of matter but it can exchange energy with the surroundings. if the water bottle is insulated really well then it will be an isolated system because it will not ...
by 205291012
Thu Feb 06, 2020 10:12 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Enthalpy versus heat
Replies: 11
Views: 85

Re: Enthalpy versus heat

yes, that is correct.
delta H = q when no work is done. So assume they're the same when no work is being done by or on the system.
by 205291012
Thu Feb 06, 2020 10:11 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: U vs H
Replies: 15
Views: 208

Re: U vs H

delta U is the change in internal energy versus delta H is the change in enthalpy.
by 205291012
Thu Feb 06, 2020 10:10 pm
Forum: Calculating Work of Expansion
Topic: Kelvin vs Celsius
Replies: 5
Views: 37

Re: Kelvin vs Celsius

if it just delta T then change in celsius will be the same as change in kelvin. you can try it out.
But if for instance, you're using the ideal gas law PV = nRT then you have to use Kelvin.
by 205291012
Thu Feb 06, 2020 10:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 4B.5 Conversion
Replies: 4
Views: 35

Re: 4B.5 Conversion

convert torr to atm. 760 torr = 1 atm.
then you will get the answer in L*atm.
multiple this with 101.325 J/ L*atm.
L*atm will cancel out. The final answer will be in joules.
by 205291012
Thu Feb 06, 2020 10:07 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Delta U equals zero
Replies: 7
Views: 73

Re: Delta U equals zero

delta U would be 0 if it is isothermal and no work is done. imagine a gas expanding in a vacuum with constant temperature. since it is not pushing against anything, no work is done and there is no change in temperature so delta U is 0.
by 205291012
Thu Feb 06, 2020 10:05 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work done on or by the system
Replies: 4
Views: 33

Re: Work done on or by the system

If the system is doing work then it is losing energy so the value will be negative. If work is done on the system, it is gaining energy so it will be positive. similarly, if a system loses heat, it is negative. if it gains heat, it is positive.
by 205291012
Thu Feb 06, 2020 10:00 pm
Forum: Calculating Work of Expansion
Topic: Isothermal
Replies: 17
Views: 122

Re: Isothermal

isothermal refers to the system being at constant temperature.
by 205291012
Thu Feb 06, 2020 9:57 pm
Forum: Calculating Work of Expansion
Topic: Constant Pressure
Replies: 3
Views: 27

Re: Constant Pressure

There is no expansion work done at constant volume. This is because for expansion work to be done the piston needs to move from a lower volume to a higher volume.

There is expansion work done at constant pressure.
by 205291012
Thu Feb 06, 2020 9:53 pm
Forum: Phase Changes & Related Calculations
Topic: Thermochemistry outline
Replies: 1
Views: 26

Re: Thermochemistry outline

combustion of fossil fuels releases carbon dioxide and other greenhouse gases into the environment. these gases are responsible for trapping heat in the atmosphere which contributes to global warming.
by 205291012
Thu Feb 06, 2020 9:50 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: 4B.13a
Replies: 3
Views: 31

Re: 4B.13a

The constant is important because the final unit of work done must be in Joules not in L*atm.
by 205291012
Thu Feb 06, 2020 9:49 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Combustion Reactions
Replies: 4
Views: 38

Re: Combustion Reactions

A combustion reaction will have the form:

CnHm + (n + m/4) O2 --> nCO2 + m/2 H2O + Heat

so it will be a hydrocarbon + oxygen gas ---> carbon dioxide + water + heat
by 205291012
Thu Feb 06, 2020 9:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: reversible vs irreversible work
Replies: 4
Views: 27

Re: reversible vs irreversible work

in thermodynamics, the external pressure is not constant for a reversible process. Here, internal pressure is equal to the external pressure. If you increase the external pressure by a very small amount, the piston will compress. Reversible process always does more work and the change is gradual and...
by 205291012
Thu Feb 06, 2020 9:39 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: aq vs gas vs liquid
Replies: 2
Views: 17

Re: aq vs gas vs liquid

solids < liquids < aqueous < gases
by 205291012
Thu Feb 06, 2020 9:37 pm
Forum: Phase Changes & Related Calculations
Topic: State functions
Replies: 7
Views: 74

Re: State functions

State functions are important because the path taken to get to the final value does not matter. State functions only depend on the current state. So for enthalpy, you can start with ice and melt it and then cool it and then melt it again and the final enthalpy will still be the same. However, work w...
by 205291012
Tue Jan 21, 2020 11:33 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: HW 5j #5
Replies: 4
Views: 38

Re: HW 5j #5

When there is compression, the side with fewer moles is favored. In this problem, both sides have the same number of moles so there is no change.
by 205291012
Tue Jan 21, 2020 11:31 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Difference in PH between strong and weak acids
Replies: 11
Views: 80

Re: Difference in PH between strong and weak acids

A strong acid has a smaller pH. A pH of 1 means it is stronger than a pH of 4. That's why a weak acid will have a higher pH than a strong acid.
by 205291012
Tue Jan 21, 2020 11:30 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 19
Views: 138

Re: Le Chatelier's Principle

The principle simply states that when stress is applied to a system in dynamic equilibrium, the the equilibrium adjusts to minimize the effects of stress. So if a system is compressed, then the equilibrium will favor whichever side has fewer moles. Other examples include adding or removing a reactan...
by 205291012
Tue Jan 21, 2020 11:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ice box approximation
Replies: 9
Views: 71

Re: ice box approximation

Use approximation when value of K is less than 10^-3. Always verify your answer by plugging the concentrations to check if you still get the same K. My TA recommended using the quadratic equation every time just to be safe.
by 205291012
Tue Jan 21, 2020 11:20 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q and K
Replies: 8
Views: 138

Re: Q and K

Q and K both measure the ratio of the concentration of products to concentration of reactants. However, K is a constant and it is the value you get when the mixture is at equilibrium. Q is the same ratio but it is measured at any point during the reaction so it can be compared to K to figure out whe...
by 205291012
Tue Jan 21, 2020 11:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: exothermic reactions
Replies: 19
Views: 126

Re: exothermic reactions

An exothermic reaction means heat is given off (similar to it being on the product side). Think of it as increasing products (or heat in this case) would favor reactants.
by 205291012
Tue Jan 21, 2020 11:16 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Using Kc Vs Kp
Replies: 18
Views: 158

Re: Using Kc Vs Kp

This depends on the information given in the question. I believe even if the molar concentrations of gases is given then you would just calculate Kc. But if the partial pressures are given then calculate Kp.
by 205291012
Tue Jan 21, 2020 11:14 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Q
Replies: 7
Views: 57

Re: Reaction Q

Q tells us which direction the reaction will proceed when you measure the ratio of reactants to products at any given time. By comparing Q to K, you can figure out if the reaction will shift towards products or reactants.
by 205291012
Tue Jan 21, 2020 11:10 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: H20 in the ICE table
Replies: 26
Views: 180

Re: H20 in the ICE table

Only if H20 is in the liquid form then do not include it in the ICE table but if it is in gaseous form then include it. Also, don't include any solids or liquids in the ICE table.
by 205291012
Sun Jan 19, 2020 4:02 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Reaction Shifts Left or Right
Replies: 15
Views: 113

Reaction Shifts Left or Right

Hi,

In discussion section 2K, we received extra homework problems. The equation was:
N2 (g) + 3H2 (g) --> 2NH3 (g) + heat
If we increase temperature, why does the reaction shift to the left?

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