CHEMISTRY COMMUNITY

Long Luong 2H

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

Long Luong 2H

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

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

For isothermal reversible expansion, the change is occurring over infinitesimally small steps. On the other hand, irreversible expansion occurs instantly over a constant pressure.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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+/...

Long Luong 2H

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...

Long Luong 2H

Why is $E^{\circ}$ = 0? In what scenarios is $E^{\circ}$ = 0?

Long Luong 2H

From Appendix 2B,
In3+ + e- -> In2+ is -0.49V
U4+ + e- -> U3+ is -0.61V

Long Luong 2H

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.

Long Luong 2H

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?

Long Luong 2H

When either reactants increase or products decrease, cell potential increases. When either reactants decrease or products increase, cell potential decreases.

Long Luong 2H

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.

Long Luong 2H

By using an external power source, you can drive a non-spontaneous redox reaction forward.

Long Luong 2H

When balancing redox reactions under basic conditions.

Long Luong 2H

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

The Nernst equation calculates cell potential based on concentration. It is E $E = E^\bigcirc - \frac{RT}{nF}lnQ$ .

Long Luong 2H

Platinum is the most common electrode because it is an inert conductor. It will not react with and affect the redox reaction.

Long Luong 2H

To add to this answer, the units for volts are 1 Joule per coulomb, which specifies a certain amount in one coulomb.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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).

Long Luong 2H

A reversible reaction proceeds in infinitesimally small steps and can go in either direction. An irreversible reaction occurs instantaneously and cannot be reversed.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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 ...

Long Luong 2H

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....

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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

Long Luong 2H

Delta H is the change in enthalpy. Delta U is the change in the internal energy of the system.

Long Luong 2H

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...

Long Luong 2H

You won't have to calculate it. We will most likely have to refer to a table with enthalpy values.

Long Luong 2H

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...

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

Heat pertains to thermal energy, whereas work pertains to mechanical energy. Work is a means of transferring energy.

Long Luong 2H

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.

Long Luong 2H

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).

Long Luong 2H

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...

Long Luong 2H

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.

Long Luong 2H

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.

Long Luong 2H

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 ...

Long Luong 2H

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!

Long Luong 2H

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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