Search found 30 matches

by RachelCheung1A
Sat Mar 16, 2019 12:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Galvanic cells and K
Replies: 3
Views: 14

Re: Galvanic cells and K

I would use the equation of E=R*T/(nF)*lnK. Isolate K to solve, assuming you have values for the other variables or the information needed to solve them.
by RachelCheung1A
Tue Mar 12, 2019 4:39 pm
Forum: Ideal Gases
Topic: units
Replies: 15
Views: 97

Re: units

The units in K should cancel out so there shouldn't be any units for K.
by RachelCheung1A
Tue Mar 12, 2019 4:30 pm
Forum: Zero Order Reactions
Topic: Reaction Rate
Replies: 10
Views: 41

Re: Reaction Rate

Yes as long as it is the same formula and under same conditions (ex. temp)
by RachelCheung1A
Mon Mar 11, 2019 10:12 pm
Forum: First Order Reactions
Topic: Units of Rate Constant
Replies: 5
Views: 22

Re: Units of Rate Constant

Not necessarily. As long as the units can cancel out, you can do seconds, minutes, hours, etc.
by RachelCheung1A
Mon Mar 11, 2019 10:10 pm
Forum: Administrative Questions and Class Announcements
Topic: Final Exam Topics
Replies: 8
Views: 64

Re: Final Exam Topics

Yep everything up to and including Wednesday
by RachelCheung1A
Mon Mar 11, 2019 3:44 pm
Forum: First Order Reactions
Topic: First order rxn graphs [ENDORSED]
Replies: 4
Views: 24

Re: First order rxn graphs [ENDORSED]

They all have time on the x axis
Zero order has [A] on the y axis and slope is -k
First order has ln[A] on the y and slope is also -k
Second order has 1/[A] on the y and slope is k
by RachelCheung1A
Mon Mar 11, 2019 3:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Frequency Factor
Replies: 5
Views: 20

Re: Frequency Factor

It is the number for the frequency of collisions between reactants.
by RachelCheung1A
Mon Mar 11, 2019 3:19 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: "Bottle Neck" Pre-equilibrium Approach
Replies: 1
Views: 11

Re: "Bottle Neck" Pre-equilibrium Approach

The Pre-equilibrium approach assumes that the reaction has steps in the order of a fast step, then a slow step. The fast step will produce intermediates needed for the slow step and because the slow step is slow, there will be a build up of intermediates and we can assume that it will be at equilibr...
by RachelCheung1A
Sun Feb 24, 2019 6:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Ecell
Replies: 13
Views: 119

Re: Ecell

Ecell can be calculated by subtracting the reduction potential of the half reaction that is oxidized from the reduction potential of the half reaction that is reduced.
by RachelCheung1A
Sun Feb 24, 2019 6:49 pm
Forum: Balancing Redox Reactions
Topic: Order to balance
Replies: 6
Views: 36

Re: Order to balance

In half reactions, balance elements first, H and O second, electric charges third and then electrons last.
by RachelCheung1A
Sun Feb 24, 2019 6:48 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Spontaneous?
Replies: 6
Views: 49

Re: Spontaneous?

If the change in Gibbs free energy is negative, then it it spontaneous
by RachelCheung1A
Mon Feb 18, 2019 11:17 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: TEST 3
Replies: 7
Views: 70

Re: TEST 3

All topics on Gibbs free energy and electrochemistry
by RachelCheung1A
Mon Feb 18, 2019 11:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: standard Gibbs Free Energy
Replies: 4
Views: 31

Re: standard Gibbs Free Energy

Standard gibbs energy is denoted by the little degree-like symbol and indicates the gibbs energy when the process is under 1 atm and 25 degrees C.
by RachelCheung1A
Mon Feb 18, 2019 11:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Internal energy (U) of an isolated system
Replies: 17
Views: 142

Re: Internal energy (U) of an isolated system

In an isolated system, there is no exchange of energy with surroundings and therefore the internal energy stays the same and delta U is 0
by RachelCheung1A
Mon Feb 18, 2019 11:08 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Isolated system
Replies: 10
Views: 84

Re: Isolated system

Heat and matter cannot be moved in or out of the bomb calorimeter
by RachelCheung1A
Mon Feb 18, 2019 11:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Negative Delta G
Replies: 7
Views: 51

Re: Negative Delta G

When delta H is negative and delta S is positive, it will definitely be negative delta G.
A large negative delta H and a small negative delta at a low temperature can possibly result in a negative delta G
by RachelCheung1A
Sat Feb 09, 2019 3:57 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: When to use deltaS=q/t versus deltaS=nRlnV2/V1
Replies: 2
Views: 36

Re: When to use deltaS=q/t versus deltaS=nRlnV2/V1

Use deltaS=q/t when q (heat transferred) and temperature is given. Use deltaS=nRlnV2/V1 when moles and volume change is given.
by RachelCheung1A
Sat Feb 09, 2019 3:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: When do you use w = -nRTlnV2/v1, q = nRTlnV2/V1, and w = -PdV?
Replies: 1
Views: 14

Re: When do you use w = -nRTlnV2/v1, q = nRTlnV2/V1, and w = -PdV?

Use w=nRTlnV2/V1 when solving for work done by a reversible, isothermal gas expansion process with Volume change. Use w=-PdV for irreversible gas work. q is for heat transferred but I think that specific equation is not frequently used.
by RachelCheung1A
Sat Feb 02, 2019 12:23 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Delta U
Replies: 3
Views: 301

Re: Delta U

Delta U only requires the Final and Initial numbers of U and anything that takes place in between (the path) does not matter. Because delta U just means the change of U from the beginning to the end, it is a state function.
by RachelCheung1A
Sat Feb 02, 2019 12:14 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: open system
Replies: 8
Views: 79

Re: open system

When the beaker is open, it experiences a constant pressure since the pressure it experiences is the atmospheric pressure around it which will not change since the atmosphere is too large for any change to be considered significant.
by RachelCheung1A
Sun Jan 27, 2019 9:30 pm
Forum: Phase Changes & Related Calculations
Topic: State Properites
Replies: 7
Views: 59

Re: State Properites

State properties do not depend on the path taken; they depend on the state of the substance. Work and heat are not considered because they take into account the path taken. Ex. In work, the formula is force times distance. If you have two molecules at the same starting point, molecule A that reaches...
by RachelCheung1A
Sun Jan 27, 2019 9:19 pm
Forum: Ideal Gases
Topic: Approximations for ICE
Replies: 20
Views: 142

Re: Approximations for ICE

when the K is less than 1x10-3, so if the K ends with 10^-4 or smaller. Ex 1.9x10^4 approximate but 1.9x10^-3 don't approximate
by RachelCheung1A
Sun Jan 27, 2019 9:15 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Catalysts in Kc
Replies: 6
Views: 54

Re: Catalysts in Kc

They increase the rate of the reaction but does not cause any permanent chemical change in the reaction, so the concentrations are the same and equilibrium is the same
by RachelCheung1A
Sun Jan 27, 2019 9:12 pm
Forum: Phase Changes & Related Calculations
Topic: Phase Changes
Replies: 7
Views: 57

Re: Phase Changes

They are both endothermic because they need to take in heat to break bonds and change phase
by RachelCheung1A
Mon Jan 21, 2019 5:10 pm
Forum: Calculating the pH of Salt Solutions
Topic: pH of acids
Replies: 8
Views: 107

Re: pH of acids

Strong acid will have lower pH because it has a full dissociation into more H30+ than a weak acid. pH relies on the amount of H30+ ions (-logH30+) and so more H30+ ions will cause the pH to be lower since you are logging the molarity.
by RachelCheung1A
Mon Jan 21, 2019 5:07 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5% rule
Replies: 11
Views: 92

Re: 5% rule

If the % pronotation is less than 5, then approximation (disregarding the initial change of x in the denominator) is valid.
by RachelCheung1A
Thu Jan 10, 2019 4:41 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6th edition, 11.7?
Replies: 4
Views: 74

Re: 6th edition, 11.7?

Thanks that's really helpful. Just wanted to know why would 5/17 be used for the calculation of partial pressure instead of 6/11 from the earlier part B?
by RachelCheung1A
Thu Jan 10, 2019 4:29 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: H2O
Replies: 5
Views: 36

Re: H2O

Yes, water in gas form in included, however water in liquid form is not.
by RachelCheung1A
Thu Jan 10, 2019 4:22 pm
Forum: Ideal Gases
Topic: Reaction Quotient
Replies: 6
Views: 46

Re: Reaction Quotient

We disregard solids and liquids because their concentrations are the same throughout the reaction. Concentration equals to density divided by molar mass and both solids and liquids' densities are pretty much constant, therefore concentrations of solids and liquids are constant.

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