Search found 49 matches

by 805329408
Sun Mar 08, 2020 6:04 pm
Forum: Zero Order Reactions
Topic: slope of zero order reaction
Replies: 2
Views: 23

slope of zero order reaction

Why is the slope of a zero order reaction always negative compared to a first or second order reaction which are negative and positive respectively?
by 805329408
Sun Mar 08, 2020 5:50 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: thermodynamically stable
Replies: 6
Views: 81

Re: thermodynamically stable

For something to be thermodynamically stable, it has to be spontaneous right? Even though it will not react I think for something to be thermodynamically stable, it is non spontaneous since it is unlikely to move to a higher energy on its own, making it stable thermodynamically. On the other hand, ...
by 805329408
Sun Mar 08, 2020 5:46 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: 7A.15
Replies: 5
Views: 35

Re: 7A.15

Since C is a zero order reaction, you can ignore it when solving for A and B because that portion would just cancel out to 1/1 since they are both to the zeroth power.
by 805329408
Sun Mar 08, 2020 5:38 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: collision theory
Replies: 2
Views: 46

collision theory

does anyone know if we will be going over collision theory this upcoming week during lecture?
by 805329408
Sun Mar 08, 2020 5:32 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: instantaneous rate
Replies: 16
Views: 152

Re: instantaneous rate

Since the graph is a curve, taking the average rate will treat the graph as a line instead and not account for the curve which an instantaneous rate does.
by 805329408
Sun Mar 01, 2020 5:22 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6O.1 and 6O.3
Replies: 2
Views: 117

6O.1 and 6O.3

For problem 6O.1 we chose the cathode to be the nickel reaction which had a smaller or more negative E and this makes sense because the reaction is electrolyzed which means that a non spontaneous reaction was driven by an outside current allowing for the cathode to have a smaller E than that of the ...
by 805329408
Sun Mar 01, 2020 4:51 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: electrolysis
Replies: 6
Views: 80

electrolysis

when a problem states that a reaction is electrolyzed, can we assume that the reaction is non spontaneous?
by 805329408
Sun Mar 01, 2020 2:41 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 6N.17
Replies: 1
Views: 32

6N.17

For the maximum work of this reaction, why is the answer shown to be positive? Shouldn't it be negative because the equation for Wmax= -nFE and E needs to be positive in this case in order for the cell to do work? Thanks in advance!
by 805329408
Fri Feb 28, 2020 12:22 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: concentration cells
Replies: 5
Views: 67

concentration cells

what determines whether something is a concentration cell or not? for example, in 6N3, how do we determine which reactions are concentration cells? Thanks in advance!
by 805329408
Tue Feb 25, 2020 10:25 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: When to apply Pt into cell diagrams
Replies: 9
Views: 90

When to apply Pt into cell diagrams

How do you know when to apply Pt(S) as the inert conductor in a cell diagram besides the fact that you have elements in the same phase? Thanks in advance!
by 805329408
Mon Feb 24, 2020 11:14 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in the change in free gibbs energy equation
Replies: 4
Views: 63

n in the change in free gibbs energy equation

How do you find n? Is it number of moles of products minus reactants? vice versa? or is it just the change in moles which means it is always positive? thanks in advance!
by 805329408
Sun Feb 23, 2020 11:02 pm
Forum: Balancing Redox Reactions
Topic: 6K.3D balancing problem?
Replies: 4
Views: 42

Re: 6K.3D balancing problem?

Can someone explain why we can write Cl2 -> 2 Cl- please?
by 805329408
Sun Feb 23, 2020 11:00 pm
Forum: Balancing Redox Reactions
Topic: Half reactions
Replies: 17
Views: 194

Re: Half reactions

A half reaction is balanced, when the charges on both sides of the half reaction are balanced and also when the elements themselves are balanced.
by 805329408
Sun Feb 23, 2020 10:56 pm
Forum: Balancing Redox Reactions
Topic: Reduction?
Replies: 13
Views: 116

Re: Reduction?

If you figure out the oxidation numbers of each molecule, the group where the oxidation number decreases is the portion of the redox reaction that is reduced since it is gaining a more negative charge, meaning it is gaining electrons.
by 805329408
Sun Feb 23, 2020 10:54 pm
Forum: Balancing Redox Reactions
Topic: Oxidation?
Replies: 10
Views: 137

Re: Oxidation?

If you figure out the oxidation numbers of each molecule, the group where the oxidation number increases is the portion of the redox reaction that is oxidized since it is gaining a more positive charge, meaning it is donating its electrons.
by 805329408
Sun Feb 23, 2020 10:52 pm
Forum: Balancing Redox Reactions
Topic: Determining direction of flow
Replies: 15
Views: 175

Re: Determining direction of flow

Because the direction of flow is always from anode (negative charge) to cathode (positive charge) and the anode is always on the left while the cathode is on the right, the direction that the electron flows is always from left to right.
by 805329408
Sun Feb 16, 2020 1:06 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: spontaneity
Replies: 34
Views: 633

Re: spontaneity

jisulee1C wrote:Gibbs Free Energy. If delta G is negative you know that the forward reaction is spontaneous.


Why is it Gibbs Free Energy vs, using enthalpy or entropy.
by 805329408
Sun Feb 16, 2020 1:04 pm
Forum: Van't Hoff Equation
Topic: concept help
Replies: 4
Views: 74

Re: concept help

The Van't Hoff equation allows us to relate the equilibrium constant with temperature and also change in enthalpy and entropy.
by 805329408
Sun Feb 16, 2020 1:01 pm
Forum: Balancing Redox Reactions
Topic: Number of electrons
Replies: 5
Views: 39

Re: Number of electrons

Yes that would make sense since in a oxidation reaction, you are losing electrons which would now be written separately in the products side of the equation.
by 805329408
Sun Feb 16, 2020 12:59 pm
Forum: Van't Hoff Equation
Topic: equilibrium and gibbs energy
Replies: 2
Views: 26

Re: equilibrium and gibbs energy

At equilibrium, delta G is 0 because the equation for it is deltaG= -RTlnK, and if K is at equilibrium, then K =1 and taking the natural log of 1 would give you zero.
by 805329408
Sun Feb 16, 2020 12:56 pm
Forum: Balancing Redox Reactions
Topic: class example
Replies: 2
Views: 29

class example

Just to clarify, in class Lavelle used the example:
8H+ + MnO4- + 5e- = Mn+2 + 4H2O where he said Mn is reduced from +7 to +2

Mn is initially +7 because O4 is is -8 and in order for the overall molecule to have a negative charge, Mn has to be +7 right? Thanks in advance!
by 805329408
Mon Feb 10, 2020 9:31 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Entropy of Surroundings vs Entropy of Systems
Replies: 1
Views: 32

Entropy of Surroundings vs Entropy of Systems

For reversible reactions, the delta s system is always equivalent to negative delta s surroundings which is equal to delta s system. However, for irreversible reactions, is delta s surroundings always equal to 0? Why? Thanks in advance!
by 805329408
Sun Feb 09, 2020 7:27 pm
Forum: Ideal Gases
Topic: Change in pressure
Replies: 7
Views: 131

Re: Change in pressure

Increasing the pressure will shift the reaction to the side with less moles of gas.
by 805329408
Sun Feb 09, 2020 7:24 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 4I.3: Negative Entropy?
Replies: 1
Views: 34

Re: 4I.3: Negative Entropy?

The answer is negative because the question is asking for the standard entropy change of the surroundings specifically and not the system so the standard entropy change of the system should be equivalent to the negative standard entropy change using the idea that when a system loses, its surrounding...
by 805329408
Sun Feb 09, 2020 7:20 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Intensive vs Extensive
Replies: 7
Views: 88

Re: Intensive vs Extensive

Entropy is an extensive property because it depends on the quantity of each. For example, if you have a 6 atom molecule and a 3 atom molecule, the 6 atom molecule has a higher entropy since it can occupy more states than the latter. So in this case, since the entropy of the two molecules was depende...
by 805329408
Sun Feb 09, 2020 7:12 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs Irreversible
Replies: 7
Views: 139

Re: Reversible vs Irreversible

For a reversible system, the system is isothermal and thus temperature is constant which impacts the formulas utilized since some are used for temperature change and some are used when temperature is constant which is the case of a isothermal, reversible system.
by 805329408
Sun Feb 09, 2020 1:12 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4.19
Replies: 1
Views: 36

4.19

Calculate the molar kinetic energy (in joules per mole) of Kr(g) at (a) 55.85 8C and (b) 54.85 8C.

What equation are we supposed to use to start this problem?
by 805329408
Tue Feb 04, 2020 5:40 pm
Forum: Phase Changes & Related Calculations
Topic: 4.7
Replies: 1
Views: 28

4.7

Calculate the work that must be done against the atmo- sphere for the expansion of the gaseous products in the combus- tion of 1.00 mol C6H6(l) at 25 8C and 1.00 bar

Can anyone give me insight on how to start this problem?
by 805329408
Sun Feb 02, 2020 10:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: q vs H
Replies: 9
Views: 59

q vs H

When given the term, "heat transfer" is this referring to q or H?
by 805329408
Sun Feb 02, 2020 11:53 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.13
Replies: 3
Views: 34

Re: 4A.13

The first step is to find the heat capacity that is calibrated by the calorimeter. To do this use the eqaution C=q(calorimeter)/change in T. Essentially you would do C=(3.50kJ)/(7.32K) = 0.478kJ/K. Then you can use this heat capacity to calculate the heat released by the reaction. So set up the equ...
by 805329408
Sun Feb 02, 2020 10:59 am
Forum: Calculating Work of Expansion
Topic: Pressure in Reversible/Irreversible Expansion
Replies: 3
Views: 43

Re: Pressure in Reversible/Irreversible Expansion

Can someone explain how the equation for work for a reversible expansion is derived? or be more specific when you say the integral is taken? Thanks!
by 805329408
Sun Feb 02, 2020 10:54 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Hess's Law
Replies: 2
Views: 31

Re: Hess's Law

Hess's law states that the total enthalpy change for a reaction is the sum of all changes regardless of however many steps a reaction has because enthalpy is a state property. It is typically used when you are given two or more reactions along with their corresponding enthalpy changes and asked to c...
by 805329408
Sun Feb 02, 2020 10:49 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 6
Views: 85

Re: Bond Enthalpies

Bonds that are formed are negative in enthalpy calculations because energy is released when bonds are formed and the system loses energy.
by 805329408
Sun Feb 02, 2020 10:47 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.7
Replies: 3
Views: 48

Re: 4A.7

You add the q of the water and the kettle because the water in the kettle is part of the entire system now and in order to raise the kettle to the boiling point of water, the water inside needs to be raised too and thus you add the two q's.
by 805329408
Sat Jan 25, 2020 5:25 pm
Forum: Phase Changes & Related Calculations
Topic: Endothermic and Exothermic
Replies: 13
Views: 91

Re: Endothermic and Exothermic

If heat is flowing out, the reaction is exothermic, and if heat is being absorbed, the reaction is endothermic. A trick I like to use to remember this is by looking at the first two letters of each word, in "exothermic" heat is "EXiting" and in "endothermic" heat is &qu...
by 805329408
Sat Jan 25, 2020 5:22 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Decreasing volume
Replies: 5
Views: 49

Re: Decreasing volume

I like to think of it as the system relieving itself of the increase in pressure in order to balance itself out or reach equilibrium again by shifting to the side with less moles of gas.
by 805329408
Sat Jan 25, 2020 5:20 pm
Forum: Phase Changes & Related Calculations
Topic: 4A.1
Replies: 1
Views: 52

Re: 4A.1

This calculate change in volume because the negative value means the volume is decreasing and also the height used which should be 20 cm is how much the pump was depressed which is then multiplied to the area of the base. The reason why this is calculating the change in volume is because the pump is...
by 805329408
Sat Jan 25, 2020 5:16 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 4A.3
Replies: 3
Views: 53

Re: 4A.3

You would use the equation for work where W (work) = - P (work constant) x change in V. In this case you would need to calculate the change in volume first with the information given and following that, multiply it by 2.00 atm which is the work constant in this case. Your change in V should be negat...
by 805329408
Sat Jan 25, 2020 5:12 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: bond enthalpy calculations
Replies: 2
Views: 23

Re: bond enthalpy calculations

I believe it is used to account for the phase change and bond enthalpy when calculating overall reaction enthalpy.
by 805329408
Sat Jan 18, 2020 11:28 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Decreasing pressure
Replies: 4
Views: 44

Re: Decreasing pressure

Why does the reaction shift to the side with less moles of gas when pressure increases? And why does the reaction shift to the side with more moles of gas when pressure decreases?
by 805329408
Sat Jan 18, 2020 11:25 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Ka and Kb
Replies: 3
Views: 13

Ka and Kb

When do we know when to use Ka and Kb when given a reaction equation?
by 805329408
Sat Jan 18, 2020 11:22 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K and Kc
Replies: 3
Views: 37

Re: K and Kc

K and Kc are the same thing, they both are equilibrium constants, like the last person said, Kc just specifies that it is the constant for concentration while on the other hand, Kp, is the constant for pressure at equilibrium.
by 805329408
Wed Jan 15, 2020 5:09 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5.39
Replies: 4
Views: 85

Re: 5.39

I am still confused on where the 1/6.1*10^-3 comes from because I get that the table gives us the reverse reaction of what we want and in order to find the Kc of this reaction, we have to take the reciprocal of it. However, according to the table, the Kc for the reverse reaction is 6.1x10^23 and if ...
by 805329408
Thu Jan 09, 2020 11:33 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5H.3
Replies: 4
Views: 55

Re: 5H.3

Does anyone know what the very last column is used for?
by 805329408
Thu Jan 09, 2020 11:28 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K values
Replies: 4
Views: 51

Re: K values

I believe that if K< 10^-3 than the reaction STRONGLY favors reactants, but if it is greater than this cutoff, it still favors reactants but not strongly? The same goes for if K> 10^3, the reaction strongly favors products but if under the cutoff, then it still favors products but not strongly.
by 805329408
Thu Jan 09, 2020 11:25 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: ice tables
Replies: 3
Views: 284

Re: ice tables

Ice tables demonstrate the initial concentrations, change in concentration and equilibrium concentration. So yes, by using an ice table you can not only determine the difference in concentrations but can also calculate the change.
by 805329408
Thu Jan 09, 2020 11:21 am
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Q vs K
Replies: 8
Views: 75

Re: Q vs K

The reason why the reaction moves forward when the reaction quotient (Q) is less than the equilibrium constant (K) is because the lesser value means that there is less product than there should be when the reaction reaches equilibrium and thus more product is needed, so the reaction moves forward. A...
by 805329408
Thu Jan 09, 2020 11:14 am
Forum: Administrative Questions and Class Announcements
Topic: Homework 1
Replies: 18
Views: 248

Re: Homework 1

For asking a question on chemistry community, just select the "New Topic" tab in the top left corner. First go back to the main Chem 14B page, from there you should be able to select a topic in the tabs below, and when you do, the "New Topic" button in the corner should appear. H...
by 805329408
Thu Jan 09, 2020 11:07 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Value of Kc and Kp
Replies: 6
Views: 51

Re: Value of Kc and Kp

The value of the equilibrium constant when calculating using concentration versus pressure should be the same. I believe the constant only changes if you alter the temperature of the reaction but when alternating between concentration and pressure, the constant should remain the same.

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