Search found 27 matches

by Philomena 4F
Mon Mar 16, 2020 5:51 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: factors of Gibbs free energy
Replies: 2
Views: 95

Re: factors of Gibbs free energy

delta G is more positive when the partial pressure of the product/s increases.
delta G is more negative when the partial pressure of the reactant/s increases.
by Philomena 4F
Mon Mar 16, 2020 5:43 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst K vs Q
Replies: 5
Views: 109

Re: Nernst K vs Q

If you use K, that means you are using the ratio of products to reactants at equilibrium. This would give you E of 0, as a battery or cell is essentially dead at equilibrium. Voltage is generated by electron flow, and electrons flow until the system reaches equilibrium. Thus once equilibrium has be...
by Philomena 4F
Mon Mar 16, 2020 5:33 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Finding the concentration of cathodes/ anodes
Replies: 2
Views: 64

Re: Finding the concentration of cathodes/ anodes

Yes, you can use the Nernst equation, provided all the other info is given. If it's a concentration cell, the cathode is the half-cell with the higher concentration, so it'll be the reactant. If it's a normal galvanic cell, you would identify the reactant and product from the overall equation of th...
by Philomena 4F
Mon Mar 16, 2020 5:26 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: calculating standard cell potential
Replies: 6
Views: 93

Re: calculating standard cell potential

You have to determine which of the half rxns is the cathode (reduction) and anode (oxidation). Then you plug in the given E values for those reactions to the formula Ecell = Ecat - Ean.
by Philomena 4F
Mon Mar 16, 2020 5:18 pm
Forum: General Rate Laws
Topic: Rate Constants
Replies: 3
Views: 112

Re: Rate Constants

To be pseudo-first-order, the concentration of one of the reactants in the rate law must be increased to be much larger than the concentration of the other reactant. For example, look at #15 from ENDGAME. The concentration of A has been increased so much that even when A is used up by the reaction,...
by Philomena 4F
Mon Mar 16, 2020 5:01 pm
Forum: First Order Reactions
Topic: size
Replies: 6
Views: 114

Re: size

I read that if a particle (ie. solid reactant) is broken down into small bits, it leads to greater surface area and a faster reaction rate. But it doesn't affect the formed products in any way.
by Philomena 4F
Sun Mar 01, 2020 11:55 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: Importance of pH?
Replies: 2
Views: 50

Re: Importance of pH?

Deepika Reddy 1A wrote:I believe that it is important because it determines how you balance the redox half-reactions. Depending on whether the solution is acidic or basic, the solution is balanced differently.


Can you pls tell me the different approach on balancing a rxn based on acidity/basicity?
by Philomena 4F
Sun Mar 01, 2020 11:48 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Voltage vs Gibbs
Replies: 2
Views: 53

Re: Voltage vs Gibbs

A negative Gibbs free energy means a spontaneous reaction. From the eq deltaG= -nFE, a positive E will still result to a negative value. If it's a negative E, then deltaG would be positive since the negative sign in front of n will be cancelled out and turn to a positive sign. That in turn will be a...
by Philomena 4F
Sun Mar 01, 2020 11:37 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Free energy
Replies: 3
Views: 63

Re: Free energy

If Ecell > 0, then the deltaG is more negative. That shows a spontaneous reaction.
by Philomena 4F
Sun Mar 01, 2020 11:33 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n value
Replies: 9
Views: 141

Re: n value

It's the number of electrons transferred from the balanced half reactions (reduction and oxidation).
by Philomena 4F
Sun Mar 01, 2020 11:30 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Reduced/Oxidized based on Ecell
Replies: 6
Views: 116

Reduced/Oxidized based on Ecell

I learned that the more positive Ecell refers to the reaction being reduced. If the given Ecell for two reactions have the same value, which will be considered oxidized/reduced?
by Philomena 4F
Mon Feb 17, 2020 12:13 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy based on molecular name/structure
Replies: 2
Views: 107

entropy based on molecular name/structure

Are we supposed to know the structure of molecules according to their names to figure out their respective standard molar entropy? 4H.5 was discussed by my TA.
by Philomena 4F
Sun Feb 16, 2020 11:49 pm
Forum: Van't Hoff Equation
Topic: Van't Hoff Temperature Dependence
Replies: 4
Views: 44

Re: Van't Hoff Temperature Dependence

He mentioned in lecture that you apply this equation to calculate K at different temperatures if deltaH is given.
He broke down the equation to the ln(K2/K1) = -deltaH/R (1/T2 - 1/T1) with the assumption that deltaH is constant.
by Philomena 4F
Sun Feb 16, 2020 11:41 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: thermodynamically stable
Replies: 6
Views: 105

Re: thermodynamically stable

If deltaGf < 0, the reaction is said to be favorable and thermodynamically stable.
by Philomena 4F
Sun Feb 16, 2020 11:35 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: importance of -RTlnk
Replies: 7
Views: 67

Re: importance of -RTlnk

I believe it's simply showing the relation of K to free energy in a way that K replaces Q to show no work has been done for a reaction at equilibrium.
by Philomena 4F
Wed Feb 05, 2020 7:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Temperature
Replies: 6
Views: 94

Re: Temperature

It's endothermic reaction since the ice cube needs to absorb heat for the melting process to occur. So is an ice cube melting an example of an exothermic or endothermic reaction? Because the temperature of the water final is greater than the initial temperature and the difference would therefore be ...
by Philomena 4F
Wed Feb 05, 2020 6:40 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: higher entropies
Replies: 6
Views: 363

Re: higher entropies

Entropy is a measure of disorder/randomness. A high entropy shows an increase in disorder (low energy), which is determined by the number of microstates of the given state of matter.
by Philomena 4F
Wed Feb 05, 2020 6:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: C = K?
Replies: 5
Views: 86

Re: C = K?

It's the idea of raising the temp. by 1 degree C or K. You can use those scales interchangeably if the problem concerns delta T. Otherwise, a regular T in question would have different measured values for each scale.
by Philomena 4F
Wed Feb 05, 2020 6:17 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 6C.13
Replies: 3
Views: 56

Re: 6C.13

You rank increasing basicity by increasing pKa. I follow this pattern for figuring out this type of problem. Hope it helps!
Strong acids: High Ka, Low pKa (High pKb)
Strong bases: High Kb, Low pKb (High pKa)
by Philomena 4F
Wed Feb 05, 2020 6:12 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: approximation
Replies: 4
Views: 47

Re: approximation

Approximation of x is done if K < 10^-3. That means you can take out the x in the denominator (reactants) because it won't have a significant effect on the value you'll obtain at the end. If unsure, you can confirm the approximation when x < 5% of the initial concentration of the molecule asked to b...
by Philomena 4F
Mon Jan 20, 2020 1:01 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Adding Inert Gas
Replies: 9
Views: 123

Re: Adding Inert Gas

Diana A 2L wrote:What is considered an inert gas? Do we have to remember a list of them or is there a way to tell if a gas is inert?

My TA said that inert gas is another term for noble gases. The common ones we might see in reactions are He and Ar.
by Philomena 4F
Mon Jan 20, 2020 12:53 am
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Combining Reactions
Replies: 3
Views: 32

Re: Combining Reactions

Determining the K for the third reaction depends on the layout of its reactants/products. You might need to write the first or second reaction in reverse direction where the K becomes its inverse (1/K). But ultimately, K3=K1 x K2.
by Philomena 4F
Sun Jan 12, 2020 9:24 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K
Replies: 10
Views: 74

Re: K

Kc and Kp are both measures of equilibrium constants of a reaction based on the molar concentration and partial pressure of molecules respectively. Although they follow the same ratio of P/R, be mindful that Kc uses [] and Kp uses () while both have their coefficients in the reaction represented as ...
by Philomena 4F
Sun Jan 12, 2020 9:09 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Calculating Q
Replies: 16
Views: 182

Re: Calculating Q

Q is calculated the same way as K = [P]/[R], including only the aqueous/gas molecules. Though Q is determined for reactions that are not in equilibrium state.
by Philomena 4F
Sun Jan 12, 2020 9:06 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 5
Views: 41

Re: Le Chatelier's Principle

It's a principle that explains how a reaction adjusts and minimizes the effect of change brought by circumstances that disrupts its equilibrium state. The affecting conditions can be change in molar concentration, pressure or temperature. For instance, an increase in the molar concentration of produ...
by Philomena 4F
Sun Jan 12, 2020 8:52 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: 5.61
Replies: 3
Views: 35

Re: 5.61

The molar concentration of aqueous and gas molecules is the primary significant factor that can change the direction of an equilibrium reaction. It does not deal with pure solids and liquids, thus increasing water concentration will not shift the reaction nor influence its K value.
by Philomena 4F
Sun Jan 12, 2020 8:42 pm
Forum: Ideal Gases
Topic: ICE tables
Replies: 4
Views: 55

Re: ICE tables

ICE table aims to determine the molar concentration of a species in various set points of a reaction. Each letter represents the following: initial, change and equilibrium molar concentration. It's the best approach to calculate K of the given reaction, or figure out the composition of an equilibriu...

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