Search found 81 matches
- Mon Mar 15, 2021 11:28 pm
- Forum: General Rate Laws
- Topic: overall order of the rxn (sapling #7)
- Replies: 9
- Views: 585
Re: overall order of the rxn (sapling #7)
To my understanding you just add the orders of the reactants in the rate law together to get the overall rxn order..
- Mon Mar 15, 2021 11:27 pm
- Forum: General Rate Laws
- Topic: Units for k
- Replies: 11
- Views: 705
Re: Units for k
To be honest I just look at the right side of the equation and figure out how to make it match the left side of the equation, which is usually in units of M/s. So if it's a second order rxn, you have M/s = k (M)(M) so you can kinda figure out that the units of k need to be M^-1•s^-1
- Mon Mar 15, 2021 11:26 pm
- Forum: General Rate Laws
- Topic: Concentration Graphs to Determine Rate Law
- Replies: 4
- Views: 249
Re: Concentration Graphs to Determine Rate Law
In order to determine the rate law from concentration graphs, just examine the graphs and look for the most linear plot. The most linear plot is most indicative that the reaction is of that order.
- Mon Mar 15, 2021 11:24 pm
- Forum: General Rate Laws
- Topic: Water in Rate Law Equation
- Replies: 14
- Views: 1140
Re: Water in Rate Law Equation
Water would only be included in the rate law equation if it was part of the rate-determining (slowest) step, and an organic solvent is being used (So water is not the solvent). As long as water IS the solvent, it won't be included in the rate law.
- Mon Mar 15, 2021 11:22 pm
- Forum: General Rate Laws
- Topic: Factors Affecting k
- Replies: 83
- Views: 4556
Re: Factors Affecting k
The rate constant is affected by temperature and activation energy. Decreasing the activation energy by using a catalyst would increase the rate constant. Increasing temperature would also increase the rate constant.
- Mon Mar 15, 2021 11:20 pm
- Forum: General Rate Laws
- Topic: Intermediate
- Replies: 59
- Views: 3541
Re: Intermediate
Intermediates are produced in one step and consumed in another, and they do not show up in the overall reaction.
- Tue Mar 09, 2021 9:46 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Q in the nernst equation
- Replies: 8
- Views: 411
Re: Q in the nernst equation
You have to properly write out the redox half-reactions and combine them to get the overall balanced redox reaction. Then you plug in values for Q like you would a normal chemical equilibrium question.
- Tue Mar 09, 2021 9:45 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: mmol
- Replies: 6
- Views: 376
Re: mmol
I usually do this: example 5mmol = 5x10^-3mole
- Tue Mar 09, 2021 9:43 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Interpreting a Cell Diagram
- Replies: 5
- Views: 326
Re: Interpreting a Cell Diagram
USUALLY the anode is on the left side of the diagram and the cathode is on the right side, but do not automatically 100% assume this, as it is actually not a given. If you are given standard reduction potentials, always check and compare them to make sure that the left side really does represent the...
- Tue Mar 09, 2021 9:40 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Determining Anode and Cathode When You Don't Have Potentials
- Replies: 2
- Views: 155
Re: Determining Anode and Cathode When You Don't Have Potentials
The least positive standard reduction potential is usually the anode.
- Tue Mar 09, 2021 9:38 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: emf and max potential difference
- Replies: 2
- Views: 131
Re: emf and max potential difference
Thank you so much for this explanation, I have also been struggling with this concept.
- Tue Mar 09, 2021 9:36 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: strong reducing agent textbook 6.45
- Replies: 2
- Views: 211
Re: strong reducing agent textbook 6.45
I haven't looked at this problem specifically, but usually it depends on what other elements are involved in the reaction. For example, the reaction of iron with oxygen (Fe and O2) is going to influence which Fe standard reduction equation you use.
- Mon Mar 01, 2021 10:15 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Moles in ΔG = -nFE
- Replies: 45
- Views: 3667
Re: Moles in ΔG = -nFE
Balance the oxidation and reduction half-reactions, and the coefficient of e- is the value of "n" (moles of electrons).
- Mon Mar 01, 2021 10:13 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anode/Cathode
- Replies: 45
- Views: 1429
Re: Anode/Cathode
Anode goes on the left, cathode goes on the right.
- Mon Mar 01, 2021 10:12 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 19
- Views: 722
Re: Salt Bridge
A salt bridge prevents the buildup of charges in the two half-cells, which would stop electron flow.
- Mon Mar 01, 2021 10:11 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt bridge
- Replies: 10
- Views: 533
Re: Salt bridge
A salt bridge prevents the buildup of charge in the two half-cells so that the flow of electrons doesn't completely stop, and so the salt bridge completes the electric circuit. The cathode starts to become more negative as it receives electrons, so cations from the salt bridge flow to the cathode to...
- Mon Mar 01, 2021 10:09 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Arranging elements with best reduction ability
- Replies: 9
- Views: 534
Re: Arranging elements with best reduction ability
I like to think of it this way:
strong reducing agent - <---------------- 0 --------------> + strong oxidizing agent
strong reducing agent - <---------------- 0 --------------> + strong oxidizing agent
- Mon Mar 01, 2021 10:07 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Anodes and Cathodes
- Replies: 22
- Views: 967
Re: Anodes and Cathodes
Typically when looking at a cell diagram, the anode (oxidation) will be on the left and the cathode (reduction) will be on the right. The cathode will have a higher reduction potential as well.
- Mon Mar 01, 2021 10:05 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagrams
- Replies: 7
- Views: 409
Re: Cell Diagrams
There are 2 reactions as a part of this problem, but in general don't include H20 or electrons in cell diagrams! Also do not include stoichiometric coefficients in cell diagrams.
- Mon Mar 01, 2021 10:03 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: To Pt(s) or not to Pt(s)? - cell diagrams
- Replies: 6
- Views: 392
Re: To Pt(s) or not to Pt(s)? - cell diagrams
You only use Pt(s) when an inert metal is not provided for you to use as an electrode. I'm assuming the textbook sometimes has Pt(s) on one side of the cell diagram only because that half-reaction does not have a metal conductor given (ex: reduction of hydrogen: 2H+ + 2e- --> H2(g))
- Mon Feb 22, 2021 11:44 am
- Forum: Balancing Redox Reactions
- Topic: Oxidizing vs Reducing
- Replies: 55
- Views: 2258
Re: Oxidizing vs Reducing
I was taught OIL RIG (oxidation is loss, reduction is gain) and I remember that the agents are backwards. The oxidizing agent oxidizes the other species, and the reducing agent reduces the other species.
- Mon Feb 22, 2021 11:41 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calorimeter Calibration
- Replies: 4
- Views: 519
Re: Calorimeter Calibration
The purpose of calibrating the calorimeter is to obtain the heat capacity of the calorimeter, which you can later use to find qrxn.
- Mon Feb 22, 2021 11:39 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Can someone explain to me why work of compression is always negative?
- Replies: 12
- Views: 5723
Re: Can someone explain to me why work of compression is always negative?
From what I understand, if a gas is being compressed by a piston, work is being done ON THE GAS, and therefore work is positive. If a gas is expanding in a piston, then work is negative, because work is being done BY THE GAS.
- Mon Feb 22, 2021 11:36 am
- Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
- Topic: Units of W
- Replies: 16
- Views: 714
Re: Units of W
There are no units for degeneracy. You can see this because in the equation S = KblnW, the units of S are J.K^-1, which comes from the Boltzmann Constant
- Mon Feb 22, 2021 11:33 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: interchanging q rev and deltaH
- Replies: 6
- Views: 512
Re: interchanging q rev and deltaH
I believe you can interchange qrev and deltaH when the system is at constant pressure. Because at constant pressure, deltaH = q, we can interchange these two values in the expression deltaS = qrev/T
- Mon Feb 22, 2021 11:29 am
- Forum: Van't Hoff Equation
- Topic: Celcius vs Kelvin for T1 and T2
- Replies: 84
- Views: 6463
Re: Celcius vs Kelvin for T1 and T2
For this formula you need to use Kelvin.
- Wed Feb 17, 2021 9:52 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy: kJ or J?
- Replies: 30
- Views: 1486
Re: Entropy: kJ or J?
It's definitely J.K^-1 by default, but if you are using the equation delta G = delta H - T*delta S, you will most likely need to convert the units of delta S to kJ.mol^-1 so you can subtract it from the change in enthalpy.
- Wed Feb 17, 2021 9:51 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Positive vs Negative Entropy
- Replies: 4
- Views: 1054
Re: Positive vs Negative Entropy
Positive change in entropy means that there is an increase in disorder, meaning that it is possible for the substance to occupy more micro states than previously. Negative entropy means the reverse, that there is a decrease in disorder, and the substance will occupy less micro states because it is m...
- Wed Feb 17, 2021 9:48 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: confusion on using Cp and Cv
- Replies: 24
- Views: 1037
Re: confusion on using Cp and Cv
Cp is used for conditions of constant pressure, and Cv is used for conditions of constant volume.
- Wed Feb 17, 2021 9:48 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: confusion on using Cp and Cv
- Replies: 24
- Views: 1037
Re: confusion on using Cp and Cv
Cp is used for conditions of constant pressure, and Cv is used for conditions of constant volume.
- Wed Feb 17, 2021 9:45 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Which R Values to use
- Replies: 22
- Views: 8101
Re: Which R Values to use
It really just depends on the units used in the problem. Usually, when calculating delta G or delta S, you will use 8.314 J.K^-1.mol^-1, and when using the ideal gas law, or any other time when pressure is given, use 8.206x10^-2 L.atm.K^-1.mol^-1
- Wed Feb 17, 2021 9:43 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Meaning of K
- Replies: 55
- Views: 3686
Re: Meaning of K
I would assume K stands for the equilibrium constant, because k (or kB) is Boltzmann's Constant, and if it is temperature in Kelvin the "K" will be accompanied by a number, like in 300K.
- Wed Feb 17, 2021 9:39 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: When q=w
- Replies: 9
- Views: 421
Re: When q=w
isothermal reversible expansions have the property q=-w
- Wed Feb 17, 2021 9:38 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Useful Summary of Thermodynamic Definitions
- Replies: 55
- Views: 18357
Re: Useful Summary of Thermodynamic Definitions
This is a very helpful summary, thank you for putting this together!
- Mon Feb 08, 2021 8:52 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Sapling #18
- Replies: 2
- Views: 187
Re: Sapling #18
Thank you for posting these steps! Very helpful.
- Mon Feb 08, 2021 8:48 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 6
- Views: 269
Re: Delta U
I think the textbook defines internal energy as "the average energy of the molecules in the system." So delta U would be the change in the average energy of the molecules in the system.
- Mon Feb 08, 2021 8:46 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: lecture 14 question
- Replies: 6
- Views: 290
Re: lecture 14 question
Summing up infinitesimal changes in q results in infinitesimal changes in S, if you are wanting to know the relationship between q and S in this equation.
- Mon Feb 08, 2021 8:45 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Using R in thermodynamic equations
- Replies: 24
- Views: 975
Re: Using R in thermodynamic equations
It really just depends on the units you are looking for in the answer, and the units of the variables you are given. It seems like in thermodynamics, we use R = 8.314 J·K-1·mol-1 often, but obviously if you are given pressure in atm you are going to need the R value that has atm in it.
- Mon Feb 08, 2021 8:43 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: work and pos/neg
- Replies: 9
- Views: 474
Re: work and pos/neg
Work is positive when there is work being done on the system, and work is negative when work is being done by the system (on the surroundings).
- Mon Feb 08, 2021 8:42 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: using equations
- Replies: 11
- Views: 585
Re: using equations
What I like to do is I read the problem, and any formulas that float to my mind relating to the problem, I write down on paper. Often your brain subconsciously makes connections, and seeing a couple formulas on your page might help you discern which one is the appropriate one to use.
- Mon Feb 08, 2021 8:41 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Assuming 298 K
- Replies: 7
- Views: 276
Re: Assuming 298 K
I think it's fair to assume temp is 298K because this is STP, but I think for midterms/final Lavelle will probably specify the temperature.
- Tue Feb 02, 2021 5:12 pm
- Forum: Phase Changes & Related Calculations
- Topic: midterm respondus
- Replies: 19
- Views: 748
Re: midterm respondus
download it from CCLE but make sure to test it before every midterm, I know respondus has refused to open on my laptop because I had some settings turned on that the program wasn't compatible with. I had to edit my computer's settings in order to get respondus to work properly.
- Tue Feb 02, 2021 5:10 pm
- Forum: Phase Changes & Related Calculations
- Topic: Define Phase Change
- Replies: 78
- Views: 4919
Re: Define Phase Change
Phase change is when something transforms into another form. For example, a phase change occurs when liquid water becomes water vapor (gas).
- Tue Feb 02, 2021 5:08 pm
- Forum: Phase Changes & Related Calculations
- Topic: Endothermic v. Exothermic
- Replies: 139
- Views: 10379
Re: Endothermic v. Exothermic
Exothermic reactions will always have negative delta H because heat is being released, which is denoted with a negative sign. Endothermic reactions will always have positive delta H because heat is being absorbed, which is denoted with a plus sign.
- Tue Feb 02, 2021 5:06 pm
- Forum: Phase Changes & Related Calculations
- Topic: Water's Heating Curve
- Replies: 9
- Views: 504
Re: Water's Heating Curve
Just to add onto what has been said, during a phase change, the heating curve experiences a flat section because the added energy is being used to break bonds, so temperature does not change.
- Tue Feb 02, 2021 5:05 pm
- Forum: Phase Changes & Related Calculations
- Topic: Endothermic vs exothermic
- Replies: 24
- Views: 1647
Re: Endothermic vs exothermic
When water vapor condenses on a surface, bonds are re-forming between water molecules, and bond formation is an exothermic process (releases heat).
- Tue Feb 02, 2021 5:02 pm
- Forum: Phase Changes & Related Calculations
- Topic: Boiling water
- Replies: 25
- Views: 2798
Re: Boiling water
Boiling water breaks the hydrogen bonds in water, creating water vapor.
- Tue Feb 02, 2021 5:01 pm
- Forum: Phase Changes & Related Calculations
- Topic: when to assume x is insignificant
- Replies: 86
- Views: 6403
Re: when to assume x is insignificant
I would say if K<10^-3 then you can assume X is insignificant, and if K<10^-4 then you can DEFINITELY assume X is insignificant.
- Tue Jan 26, 2021 7:21 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Sapling #8
- Replies: 7
- Views: 475
Re: Sapling #8
For part C: Calculate the amount of CS2 produced when 399 kJ of heat is absorbed.
399kJ x 4 mol CS2/358.8kJ x (molecular weight of CS2)/1mol CS2
399kJ x 4 mol CS2/358.8kJ x (molecular weight of CS2)/1mol CS2
- Tue Jan 26, 2021 7:18 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Memorize bond enthalpies / standard enthalpies of formation?
- Replies: 39
- Views: 1232
Re: Memorize bond enthalpies / standard enthalpies of formation?
I definitely don't think you will need to memorize these, however if you wan't to get familiar with ones you see a lot (like a C-C bond) that wouldn't be a bad thing.
- Tue Jan 26, 2021 7:17 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Determining whether a reaction is Exothermic/Endothermic
- Replies: 4
- Views: 396
Re: Determining whether a reaction is Exothermic/Endothermic
Exothermic reactions have weaker reactant bonds and stronger product bonds. On the other hand, endothermic reactions have stronger reactant bonds and weaker product bonds.
- Tue Jan 26, 2021 7:15 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: endothermic vs. exothermic
- Replies: 11
- Views: 488
Re: endothermic vs. exothermic
Endothermic reactions have stronger reactant bonds (large energy requirement) and weaker product bonds (small energy release).
Exothermic reactions have weaker reactant bonds (small energy requirement) and stronger product bonds (large energy release).
Exothermic reactions have weaker reactant bonds (small energy requirement) and stronger product bonds (large energy release).
- Tue Jan 26, 2021 7:11 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Standard Enthalpy of Formation
- Replies: 10
- Views: 419
Re: Standard Enthalpy of Formation
We will definitely be given these values, don't worry too much! :)
- Tue Jan 26, 2021 7:10 pm
- Forum: Phase Changes & Related Calculations
- Topic: Midterm Scratch Paper? [ENDORSED]
- Replies: 5
- Views: 283
Midterm Scratch Paper? [ENDORSED]
I was told by my TA that we are only allowed to have a periodic table & the equation sheet in front of us when taking the midterm. Are we also allowed to have some paper for scratch work? I can't imagine doing ICE tables without writing them out.
- Sun Jan 24, 2021 8:42 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Units for ΔH
- Replies: 3
- Views: 171
Units for ΔH
When the textbook asks you to calculate the reaction enthalpy, half the time the solution manual lists the correct answer as ΔH = 35.5 kJ and half the time it lists it as ΔH=35.5 kJ.mol^-1 . I was under the impression that the latter was the correct units, but now I'm just confused. Anyone know if t...
- Tue Jan 19, 2021 5:17 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: conjugate base
- Replies: 14
- Views: 430
Re: conjugate base
This is a great demonstration of the Conjugate Seesaw:
> The stronger the acid, the weaker it's conjugate base.
>The stronger the base, the weaker its conjugate acid.
So if you have a weak acid, you must have a strong conjugate base!
> The stronger the acid, the weaker it's conjugate base.
>The stronger the base, the weaker its conjugate acid.
So if you have a weak acid, you must have a strong conjugate base!
- Tue Jan 19, 2021 5:14 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Relevance of equilibrium constant
- Replies: 5
- Views: 392
Re: Relevance of equilibrium constant
K can help you determine a lot of things about a reaction! for example:
1) Ratio of products to reactants present at equilibrium
2) How soluble the reactants are
3) the strength of an acid or base
1) Ratio of products to reactants present at equilibrium
2) How soluble the reactants are
3) the strength of an acid or base
- Tue Jan 19, 2021 5:11 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Approximately x
- Replies: 18
- Views: 616
Re: Approximately x
Lavelle has gone back and forth between saying k<10^-4 and k<10^-3 so honestly I would say as long as it's less than 10^-3 you can assume the value of X is negligible, and if it's less than 10^-4 then It's VERY reasonable to make the assumption.
- Tue Jan 19, 2021 5:06 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pKa and Ka
- Replies: 27
- Views: 827
Re: pKa and Ka
pKa is the NEGATIVE log of Ka : -log(Ka) = pKa . To convert from pKa to Ka, you would do: Ka = 10^-pKa. Just a little trick in general, the presence of that "p" (as in pH, pOH, pKa, etc) means taking the -log.
- Tue Jan 19, 2021 5:04 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Studying for Midterm #1
- Replies: 63
- Views: 2413
Studying for Midterm #1
As someone who had Dr. Scerri for chem 14A, I'm not really sure what to expect from Dr. Lavelle's midterms. Are there any tips for studying you guys would recommend? How to best prepare? Thanks so much :)
- Tue Jan 19, 2021 5:01 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Moles vs Concentrations in ICE Box
- Replies: 21
- Views: 753
Re: Moles vs Concentrations in ICE Box
I would strongly recommend putting concentrations in the ICE box, even though I know Sappling often uses moles. Using concentrations reduces the amount of steps you will need to do later, and decreases the likelihood you will make an error like forget to convert moles to molarity.
- Wed Jan 13, 2021 2:05 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Logarithms Sig Fig Rule?
- Replies: 4
- Views: 245
Logarithms Sig Fig Rule?
To my understanding, the log sig fig rule is: # of sig figs in molar concentration = # of DECIMAL PLACES in pH value for example: pH = -log( 1.8 x10^-5) = -(-4.74) = 4. 74 However, I just started doing the textbook problems, and it doesn't seem like the textbook uses this sig fig rule at all! for ex...
- Tue Jan 12, 2021 9:22 pm
- Forum: Ideal Gases
- Topic: Kc vs Kp
- Replies: 109
- Views: 4390
Re: Kc vs Kp
Kp = equilibrium constant using the equilibrium partial pressures for the reactants & products.
Kc = equilibrium constant using the equilibrium molar concentrations for the reactants & products.
Kc = equilibrium constant using the equilibrium molar concentrations for the reactants & products.
- Tue Jan 12, 2021 9:15 pm
- Forum: Ideal Gases
- Topic: Inert Gases
- Replies: 11
- Views: 263
Re: Inert Gases
When you add an inert gas to a closed system, you aren't decreasing the concentrations of the gasses already in the system, you are just adding that inert gas in as well. Because of this, K is not affected and therefore equilibrium remains unchanged.
- Tue Jan 12, 2021 9:12 pm
- Forum: Ideal Gases
- Topic: Does temperature matter?
- Replies: 19
- Views: 538
Re: Does temperature matter?
For some of the textbook questions, when you are required to look at Table 5G.2 to get the value of K, you need to make sure you are looking at the row with the correct temperature that was given in the problem, or you will end up with the wrong K.
- Tue Jan 12, 2021 9:05 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Module Question 19 [ENDORSED]
- Replies: 3
- Views: 190
Re: Module Question 19 [ENDORSED]
I just want to clarify something while I caught it --- when K<10^-3, you do NOT ASSUME THE VALUE OF X=0!! This is a mistake that Lavelle pointed out specifically in lecture. Instead, the value of X is considered to be NEGLIGIBLE, so it won't change the concentrations of the reactants a significant a...
- Tue Jan 12, 2021 9:01 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 5.61
- Replies: 2
- Views: 102
Re: Textbook Problem 5.61
I agree with what has been said above, be careful to watch out for when the question asks how adding solids/liquids affects equilibrium! The answer is it won't shift the reaction!
- Mon Jan 11, 2021 8:02 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Simplifying Expressions: K<10^?
- Replies: 6
- Views: 161
Simplifying Expressions: K<10^?
During lecture today, Dr. Lavelle said that if K<10^-3 , we can assume X is very small and it's value is negligible. However, in one of the audio-visual lectures, he said very clearly that we want to use K<10^-4 because this was a better value to use....so I just want to confirm FOR SURE which is th...
- Tue Jan 05, 2021 9:14 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Audio-Visual Module Question #15
- Replies: 3
- Views: 114
Re: Audio-Visual Module Question #15
Here's how I worked through this problem: 15. The photosynthesis reaction, 6 CO2(g) + 6 H2O(l) ⇌ C6H12O6(aq) + 6 O2(g), is endothermic. What effect will the following changes have on the equilibrium composition. a) Water is added. According to Le Chatelier's Principle, adding H20 (reactant) will cau...
- Tue Jan 05, 2021 9:06 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Question #16 from Chemical Equilibrium Part 4 Video Module
- Replies: 2
- Views: 207
Re: Question #16 from Chemical Equilibrium Part 4 Video Module
Here's how I worked through this question: The hydrolysis of ATP: ATP (aq) + H2O (l) ⇌ ADP + PO42-(aq) delta H° = -30 kJ.mol-1 The delta H for this chemical reaction is negative (-30 kJ.mol-1). This means energy is being released, and the reaction is exothermic. Heating an exothermic reaction result...
- Tue Jan 05, 2021 9:01 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Video Module Question #17
- Replies: 3
- Views: 114
Re: Video Module Question #17
Here's how I solved this problem: a) Photosynthesis: 6 CO2 (g) + 6 H2O (l) ⇌ C6H12O6(s) + 6 O2 (g) delta H° = +2802 kJ.mol-1 For this rxn notice how delta H°is positive (+2802 kJ.mol-1). Positive delta H means there is an input of energy, so this rxn is endothermic. For endothermic reactions, heatin...
- Tue Jan 05, 2021 8:54 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: H2O
- Replies: 44
- Views: 1900
Re: H2O
Water would not be included in the equilibrium constant (K) if it is in solid or liquid form. Liquids (solvents) and solids are so abundant in a chemical reaction that their molar concentrations do not change significantly during the reaction. Hopefully this reasoning helps a bit :)
- Tue Jan 05, 2021 8:49 pm
- Forum: Ideal Gases
- Topic: Bars to atm [ENDORSED]
- Replies: 41
- Views: 1713
Re: Bars to atm [ENDORSED]
While Lavelle said in one of the modules that for the purposes of this class, 1 bar=1 atm, I personally haven't come across any practice problems yet where you need to convert from bar to atm. I think you will be given one or the other, so don't worry too much :)
- Mon Jan 04, 2021 9:30 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Question 5I.15
- Replies: 1
- Views: 110
Textbook Question 5I.15
When solid NH4HS and 0.400 mol NH3(g) were placed in a vessel of volume 2.0L at 24 degrees C, the equilibrium NH4HS(s) -->NH3(g) + H2S(g), for which Kc= 1.6 x 10-4, was reached. What are the equilibrium concentrations of NH3 and H2S? My issue with this question is that the solution manual gets x= 8 ...
- Tue Oct 01, 2019 10:30 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: How to do E15
- Replies: 4
- Views: 215
How to do E15
E15 says the molar mass of the metal hydroxide M(OH2) is 74.10 g/mol. What is the molar mass of the sulfide of this metal?
I have no idea how to solve this problem, could anyone explain it to me please?
I have no idea how to solve this problem, could anyone explain it to me please?
- Tue Oct 01, 2019 10:22 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Units in Answer
- Replies: 18
- Views: 805
Re: Units in Answer
My guess would be grams but you really need the entire context of the problem to know for sure.
- Tue Oct 01, 2019 10:18 pm
- Forum: SI Units, Unit Conversions
- Topic: SIG FIGS
- Replies: 11
- Views: 569
Re: SIG FIGS
For sig figs in answers, you always use the LEAST number of sig figs. For example if you are working with 1305, 1.2, and .033333, you would use 2 sig figs for the answer because 1.2 only has 2 sig figs.
- Tue Oct 01, 2019 10:14 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Balancing Equations [ENDORSED]
- Replies: 25
- Views: 1967
Re: Balancing Equations [ENDORSED]
I'm pretty sure most of the time when you balance chemical equations, you will not need to use fractions as stoichiometric coefficients. So I'd say for the most part don't worry about it, just make sure the coefficients are ALWAYS whole numbers. You may not run into many problems with fraction coeff...
- Tue Oct 01, 2019 10:11 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Practice Problem E.1
- Replies: 6
- Views: 193
Re: Practice Problem E.1
So wait if you are given units in pm, should you always convert to m? Also how many pm's are in 1 m? Not even sure what a pm is to be honest.
- Tue Oct 01, 2019 10:08 pm
- Forum: Significant Figures
- Topic: Rounding
- Replies: 3
- Views: 190
Re: Rounding
If the number is 5 or greater, you would round up. So in the example you gave, if you only wanted 2 sig figs, 1.65 would then become 1.70, and if the number was 1.35 it would become 1.40 and so on.
- Tue Oct 01, 2019 10:05 pm
- Forum: Empirical & Molecular Formulas
- Topic: homework problem E9
- Replies: 6
- Views: 987
Re: homework problem E9
Basically MgSO4 X 7H20 is the chemical equation for magnesium sulfate heptahydrate. As you can see, "hepta" is the prefix for 7, and hydrate means H20. So in order to calculate the molar mass of magnesium sulfate heptahydrate, you need to write out the full chemical equation so you can mak...