## Search found 51 matches

Fri Mar 13, 2020 10:11 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Concentration Cells
Replies: 2
Views: 24

### Re: Concentration Cells

There’s a lot of things so I’ll let others answer, but one thing I make sure to remember is that $E^\bigcirc_c_e_l_l$
= 0
Fri Mar 13, 2020 10:07 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 6M.1
Replies: 1
Views: 23

### Re: 6M.1

Hi, what I came up with is because Ecell is negative, the Ecell = Er - El is reversed. This particular cell isn’t spontaneous.
So, to get negative (-) Ecell, the equation would be -Ecell = El - Er. In that case, -0.689V = El - 0.34 V. From there, you can add 0.34V to both sides to get El = -0.349V
Thu Mar 12, 2020 11:45 am
Forum: General Rate Laws
Topic: Units of time
Replies: 5
Views: 45

### Re: Units of time

I'd imagine you could use other units of time. Personally, I would stay uniform to the units used in the problem or whatever's specified.
Thu Mar 12, 2020 11:42 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: How do you know a cell can do work?
Replies: 7
Views: 51

### Re: How do you know a cell can do work?

Mariah wrote:
Rebekah Alfred 1J wrote:When E cell is equal to zero, the cell cannot do work.

So can the cell do work whether it is negative or positive?

The cell can do work spontaneously if E cell is positive. E cell can do work non-spontaneously in an electrolytic cell in which an external energy source supplies power.
Thu Mar 12, 2020 11:35 am
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Battery
Replies: 8
Views: 130

### Re: Battery

Yes, conceptually, there is no difference in electric potential between two cells so no electrons are being transferred between them. If the difference in electric potential is zero, no work can be done.
Wed Mar 11, 2020 10:29 pm
Forum: Second Order Reactions
Topic: 7B.13
Replies: 2
Views: 93

### Re: 7B.13

What I did was find k using the second order half-life equation. Following that, I divided the original original concentration by 16, 4, and 5 for a), b), and c). With both initial and final concentrations and k, I plugged those values into the second order integrated rate law equation to find t.
Mon Mar 09, 2020 8:48 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs Irreversible
Replies: 3
Views: 84

### Re: Reversible vs Irreversible

For isothermal reversible expansion, the change is occurring over infinitesimally small steps. On the other hand, irreversible expansion occurs instantly over a constant pressure.
Mon Mar 09, 2020 5:01 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Applying La Chateliers
Replies: 4
Views: 53

### Re: Applying La Chateliers

Yes, Ecell is the voltage created by the difference in cell potentials. For instance, in a concentration cell, the higher the difference in concentrations between the cathode and anode, the more work can be done by the voltage that is created across the electrodes.
Mon Mar 09, 2020 4:51 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration
Replies: 9
Views: 73

### Re: Concentration

Another helpful tip to know is that the cathode is usually of higher concentration and is considered a reactant. Similarly, the anode is of lower concentration is the product for Q.
Mon Mar 09, 2020 4:49 pm
Forum: Balancing Redox Reactions
Topic: 6K.3 part D
Replies: 3
Views: 49

### Re: 6K.3 part D

2Cl and Cl2- are different. 2Cl is neutral with an oxidation number of 0, whereas Cl2- is negatively charged with an oxidation number of -1.
Mon Mar 09, 2020 4:41 pm
Forum: Balancing Redox Reactions
Topic: Balancing redox with h2o
Replies: 9
Views: 124

### Re: Balancing redox with h2o

In acidic solution, you’d use H2O and H+ to balance your redox reaction, because H+ ions are present in acidic solutions. In basic solutions, you’d use H2O and -OH to balance because there’s -OH ions in basic solution. The main idea of balancing redox reactions is to use a combination of H2O and H+/...
Mon Mar 09, 2020 4:37 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration Cells
Replies: 3
Views: 55

### Re: Concentration Cells

In a concentration cell, the chemical species involved have the same element but different concentrations. When electrons from a lower concentration solution travel across the electrode, a voltage is generated. When the electrons arrive at the cathode of higher concentration, it attracts ions of the...
Thu Feb 27, 2020 12:35 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N3A
Replies: 4
Views: 79

### Re: 6N3A

Why is $E^{\circ}$ = 0? In what scenarios is $E^{\circ}$ = 0?
Thu Feb 27, 2020 12:16 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N.1
Replies: 4
Views: 113

### Re: 6N.1

From Appendix 2B,
In3+ + e- -> In2+ is -0.49V
U4+ + e- -> U3+ is -0.61V
Tue Feb 25, 2020 9:28 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Hydrogen electrodes
Replies: 1
Views: 25

### Re: Hydrogen electrodes

Hydrogen can either be H+(aq) and reduced to H2(g) or H2(g) and oxidized to H+(aq). In this reaction, there isn’t a solid to serve as an electrode so Platinum would help with that.
Tue Feb 25, 2020 9:22 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum electrode
Replies: 4
Views: 52

### Re: Platinum electrode

Betania Hernandez 2E wrote: In some cases, there may be a solid on one side already but it needs to be conducting, if not then you would include Platinum solid.

I’m a little confused by the last part of your reply. What’s an example of a solid that isn’t conducting?
Mon Feb 24, 2020 5:24 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Concentration and Cell Potential
Replies: 5
Views: 68

### Re: Concentration and Cell Potential

When either reactants increase or products decrease, cell potential increases. When either reactants decrease or products increase, cell potential decreases.
Mon Feb 24, 2020 5:13 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Maximum Potential and Voltage
Replies: 6
Views: 71

### Re: Maximum Potential and Voltage

Voltage is also the amount of work that can be done per Coulomb. So between two electrodes, when an electric current is flowing between them, it can do work.
Mon Feb 24, 2020 5:06 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Electrolytic Cells
Replies: 3
Views: 43

### Re: Electrolytic Cells

By using an external power source, you can drive a non-spontaneous redox reaction forward.
Mon Feb 24, 2020 12:36 am
Forum: Balancing Redox Reactions
Topic: Balancing Redox Reactions
Replies: 7
Views: 62

### Re: Balancing Redox Reactions

When balancing redox reactions under basic conditions.
Mon Feb 24, 2020 12:34 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation usage
Replies: 6
Views: 59

### Re: Nernst Equation usage

Matt Sanruk 2H wrote:What is the Nernst equation exactly?

The Nernst equation calculates cell potential based on concentration. It is E$E = E^\bigcirc - \frac{RT}{nF}lnQ$.
Mon Feb 24, 2020 12:29 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Platinum
Replies: 5
Views: 92

### Re: Platinum

Platinum is the most common electrode because it is an inert conductor. It will not react with and affect the redox reaction.
Mon Feb 24, 2020 12:27 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: cell potential
Replies: 3
Views: 38

### Re: cell potential

To add to this answer, the units for volts are 1 Joule per coulomb, which specifies a certain amount in one coulomb.
Wed Feb 12, 2020 1:36 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Cp and Cv
Replies: 2
Views: 42

### Re: Cp and Cv

To add on to that, for diatomic gases under constant volume, you’d use 5/2R and for constant pressure, you’d use 7/2R. These equations are used to find the heat capacity of ideal gases.
Wed Feb 12, 2020 1:33 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Calculating Enthalpy with Atoms, Linear Molecules, and Nonlinear Molecules.
Replies: 2
Views: 30

### Re: Calculating Enthalpy with Atoms, Linear Molecules, and Nonlinear Molecules.

The monatomic gases where we use (-)R are for when calculating the heat capacity of ideal gases so everything on the right side of the periodic table. You’d use 3/2R for monatomic ideal gases at constant volume. You’d use 5/2R for diatomic ideal gases at constant volume.
Wed Feb 12, 2020 1:27 am
Forum: Calculating Work of Expansion
Topic: Positive or negative work
Replies: 15
Views: 259

### Re: Positive or negative work

I like to think of a bicycle pump. When you push the pump down, you are exerting a positive force in work on the pump. However, if the gas were to push back against you, it is counteracting your work, so it’s negative work done by the pump (system).
Mon Feb 10, 2020 1:21 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: irreversible vs reversible
Replies: 3
Views: 30

### Re: irreversible vs reversible

A reversible reaction proceeds in infinitesimally small steps and can go in either direction. An irreversible reaction occurs instantaneously and cannot be reversed.
Mon Feb 10, 2020 1:05 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: extensive and intensive
Replies: 1
Views: 21

### Re: extensive and intensive

Heat capacity depends on the amount of substance present. Specific heat capacity describes the amount of energy needed to raise 1 gram of a substance by 1 degrees Celsius. Because heat capacity depends on the a non-specified amount of substance, it is extensive.
Mon Feb 10, 2020 1:01 am
Forum: Phase Changes & Related Calculations
Topic: delta T
Replies: 1
Views: 27

### Re: delta T

DeltaT would be Tfinal - Tinitial. Because it drops in temperature, let’s say to 80 degrees, Tfinal - Tinitial would be 80 - 100 = -20, indicating a drop in temperature with the negative sign.
Mon Feb 10, 2020 12:58 am
Forum: Phase Changes & Related Calculations
Topic: equation for phase changes
Replies: 3
Views: 32

### Re: equation for phase changes

Depending on the question, the deltaH fusion or vaporization is typically provided in J/mol or J/gram. With one or the other, you can convert between them with the molar mass.
Mon Feb 10, 2020 12:54 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: identifying systems
Replies: 3
Views: 49

### Re: identifying systems

It might be useful to visualize some examples. An example of an open system would be a pot on a stove where matter and energy is exchanged in the forms of ingredients and heat. A closed system would be like a rice cooker where heat is can be transferred to cook the rice, but not matter. An isolated ...
Mon Feb 03, 2020 12:06 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4C.9A
Replies: 2
Views: 27

### Re: 4C.9A

You are trying to heat the water to 100 degrees C and the copper is, in a sense, in the way. Both water and copper have different heat capacities so adding an amount of heat to one material isn't necessarily going to achieve the same temperature as adding the same amount of heat to another material....
Sun Feb 02, 2020 11:52 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: method two
Replies: 3
Views: 30

### Re: method two

Drawing out the Lewis structure is nice because you can visually see the number of bonds a certain molecule has, which will help you determine if you need to or how much to multiply the bond enthalpy by.
Sun Feb 02, 2020 11:47 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: state functions
Replies: 10
Views: 83

### Re: state functions

A state function is a property whose value is independent of the path taken to obtain the value. In other words, it doesn't matter how the particular value was achieved, but only as it exists in its current condition.
Sun Feb 02, 2020 11:42 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Energy of a system
Replies: 5
Views: 53

### Re: Energy of a system

When delta H is positive, the system absorbed heat. When delta H is negative, heat is removed. Delta H is the change in enthalpy of a system
Sun Feb 02, 2020 11:35 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Delta H and U
Replies: 3
Views: 34

### Re: Delta H and U

Delta H is the change in enthalpy. Delta U is the change in the internal energy of the system.
Sun Jan 26, 2020 11:58 pm
Forum: Phase Changes & Related Calculations
Topic: State function
Replies: 4
Views: 33

### Re: State function

I always conceptualized heat as a Thing that is passed around, while enthalpy is the net change in it. How accurate/inaccurate would that assessment be for the purpose of this class? I believe that's fair. For me, I think there must be a process to calculate heat, like a path, reaction, or change o...
Sun Jan 26, 2020 11:53 pm
Forum: Phase Changes & Related Calculations
Topic: phase changes
Replies: 5
Views: 47

### Re: phase changes

You won't have to calculate it. We will most likely have to refer to a table with enthalpy values.
Sun Jan 26, 2020 11:51 pm
Forum: Phase Changes & Related Calculations
Topic: State Property
Replies: 6
Views: 55

### Re: State Property

Of course! a state property is a value that isn't affected by how the system arrived at that state. At equilibrium, enthalpy describe the state of the system without considering how it got there. In contrast, heat doesn't describe a system but is instead a value that shows how a system changes. It d...
Sun Jan 26, 2020 11:42 pm
Forum: Phase Changes & Related Calculations
Topic: State Function
Replies: 3
Views: 22

### Re: State Function

I interpreted it as enthalpy is a state function and it therefore can be additive. Because it is a property of a system, meaning it is not affected by path taken to get the value, you can add values of enthalpy together.
Sun Jan 26, 2020 11:36 pm
Forum: Phase Changes & Related Calculations
Topic: Temp. of sample
Replies: 4
Views: 36

### Re: Temp. of sample

Yeah, if you refer to (or look up) the phase change graph, where the slopes are 0, heat is being added, yet temperature remains the same.
Sun Jan 26, 2020 11:33 pm
Forum: Phase Changes & Related Calculations
Topic: ∆H
Replies: 17
Views: 133

### Re: ∆H

Delta H is a numerical value that is a good indicator of the reaction being endothermic or exothermic. Another way can be to look at the bonds of a reaction. Overall, breaking a bond is endothermic and forming a bond is exothermic.
Sun Jan 26, 2020 11:24 pm
Forum: Phase Changes & Related Calculations
Topic: Differentiating (q) and (w)
Replies: 4
Views: 35

### Re: Differentiating (q) and (w)

Heat pertains to thermal energy, whereas work pertains to mechanical energy. Work is a means of transferring energy.
Sun Jan 26, 2020 11:19 pm
Forum: Phase Changes & Related Calculations
Topic: delta H
Replies: 3
Views: 31

### Re: delta H

Standard reaction enthalpy is the change in the total heat of the system during a chemical reaction. The standard enthalpy of formation is the change in the total heat of the system from forming a compound from elements.
Sun Jan 26, 2020 11:10 pm
Forum: Phase Changes & Related Calculations
Topic: Phase changes
Replies: 8
Views: 73

### Re: Phase changes

Eesha Sohail 1D wrote:On the heating curve, one axis is temperature, but can someone explain what exactly temperature means on a molecular level vs heat?

Heat deals with thermal energy, whereas temperature is the molecular kinetic energy (the molecules moving around in the ice/water/vapor).
Sun Jan 26, 2020 11:04 pm
Forum: Phase Changes & Related Calculations
Topic: Enthalpy of Vaporization and Fusion
Replies: 5
Views: 36

### Re: Enthalpy of Vaporization and Fusion

It may help to visualize the molecules that make up a solid, liquid and gas. When turning a solid to a gas, the molecules are more freely moving, but still packed together. However, when you turn a liquid into a gas, you are energizing the molecules so that they are quickly bouncing around completel...
Sun Jan 19, 2020 10:59 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Approximations
Replies: 2
Views: 17

### Re: Approximations

I don’t think you would need to include the (-x) for the final solution. A good way to check your approximation is the 5% rule.
Sun Jan 19, 2020 10:55 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: pKa and pKb
Replies: 17
Views: 206

### Re: pKa and pKb

PKa is calculated by the -log(kA) and pKb is calculated by the -log(kB). If you add pKa and pKb together, it will equal 14.
Sun Jan 19, 2020 10:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Acid Base Equilibria
Replies: 5
Views: 57

### Re: Acid Base Equilibria

I don't particularly understand the distinction between the K calculated through pressure of a gas and K from concentration. How are they different, and can they be converted into each other in any case? In response to Eesha, it’s the same process to calculate K, but pressure and concentration use ...
Sun Jan 19, 2020 10:35 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q < K
Replies: 16
Views: 133

### Re: Q < K

I like to think about K on a number line. If Q is less than K, it is to the left of K and is trying to go right (towards products). If Q is greater than K, it is to the right of K and trying to go left (towards products). I hope this helps!
Sun Jan 19, 2020 10:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5% rule
Replies: 8
Views: 71

### Re: 5% rule

Do you only check with the 5% rule if you make the assumption about ignoring the change in concentration of product? In other words, if you solve chemical equilibrium problems with the quadratic formula, do you check with the 5% rule?

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