Search found 51 matches
- Sat Mar 14, 2020 12:04 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: #7.11
- Replies: 2
- Views: 286
Re: #7.11
In general, the slow step is usually the rate determining step to evaluate a k value, but in general the above comment (^) is also correct.
- Sat Mar 14, 2020 12:02 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Instantaneous Rate
- Replies: 41
- Views: 2092
Re: Instantaneous Rate
As the reaction proceeds, think of it as a curved graph (seen with the equilibrium reaction graph, with E), the initial rate is very high as there is a readily amount of reactant available to react, and as its used up less reactant is available, so the reaction rate goes down (as reaction rate depen...
- Sat Mar 14, 2020 11:58 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: intermediate
- Replies: 26
- Views: 1941
Re: intermediate
The intermediate cancels out in the rate determining step (before the final overall equation), and is not present in the overall reaction --> as its presence in the reactant of one reaction and the product of another reaction, makes itself cancel out.
- Sat Mar 14, 2020 11:56 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Activation Energy
- Replies: 17
- Views: 854
Re: Activation Energy
Activation energy and enthalpy (deltaH) both have the same units of Joules, and one deals with chemical kinetics (Ea) while the other (deltaH) deals with thermodynamics.
- Sat Mar 14, 2020 11:54 am
- Forum: Environment, Ozone, CFCs
- Topic: NO3
- Replies: 6
- Views: 848
Re: NO3
If any compound is not present in the overall reaction, then it can be considered an intermediate (as it cancels out in the reactants and products). Therefore, NO3 can be considered an intermediate.
- Mon Mar 09, 2020 3:34 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: purpose
- Replies: 4
- Views: 346
Re: purpose
The purpose is to find the k value of a reaction (products or reactants favored) based on activation energy, temperature, and frequency factor (“the efficiency of a collision”)
- Mon Mar 09, 2020 3:14 pm
- Forum: *Enzyme Kinetics
- Topic: How do you tell if something is a catalyst vs an intermediate?
- Replies: 16
- Views: 5726
Re: How do you tell if something is a catalyst vs an intermediate?
An intermediate will cancel out in the overall reaction in the end (not appear), while a catalyst is not consumed in a reaction (appears in the beginning and reappears in the end).
- Mon Mar 09, 2020 3:10 pm
- Forum: *Enzyme Kinetics
- Topic: Adsorption
- Replies: 13
- Views: 3100
Re: Adsorption
In adsorption, the reactants sit on top of the solution or catalyst, while absorption (as in the class example) is when water is absorbed by a sponge (so completely different meanings and uses in context).
- Mon Mar 09, 2020 3:07 pm
- Forum: *Enzyme Kinetics
- Topic: Collision theory
- Replies: 3
- Views: 720
Re: Collision theory
In regards to the orientation and collision of atoms, the frequency factor, A, in the Arrhenius equation (k=Ae^-Ea/RT), represents the percentage of molecules in the reaction that actually collide to break and form new bonds (that becomes the products). Higher the A, the more likely the reaction is ...
- Mon Mar 09, 2020 3:04 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Derivation of Arrhenius
- Replies: 2
- Views: 652
Re: Derivation of Arrhenius
Using the k equation: k=Ae^-Ea/RT, you take the natural log of each side, and move the exponent into the coefficient. The presence of two temperatures represents the deltaT of a reaction (as a reaction may increase or decrease in temp based on if the equation is endothermic or exothermic).
- Mon Mar 09, 2020 3:02 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Intermediate Species
- Replies: 9
- Views: 659
Re: Intermediate Species
It is usually an element or compound in a series of reactions that cancels out as is not present in the overall final equation (it is consumed in the process):
A + B --> C
B + C --> E
2B + A --> E, here the intermediate is C.
A + B --> C
B + C --> E
2B + A --> E, here the intermediate is C.
- Mon Mar 09, 2020 3:00 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 28
- Views: 1624
Re: Catalysts
A catalyst will lower the activation energy (Ea) in a reaction, causing the curve of the rxn process vs energy graph curve to be lower than without a catalyst.
- Fri Feb 28, 2020 11:33 am
- Forum: Biological Examples
- Topic: atp example
- Replies: 3
- Views: 969
Re: atp example
NADH is involved in the cellular respiration pathway to produce ATP and is involved when NAD gains a hydrogen atom to create the biphosphoglycerate molecule (the NAD also abandons its inorganic phosphate).
- Fri Feb 28, 2020 11:28 am
- Forum: Biological Examples
- Topic: ATP example
- Replies: 7
- Views: 3065
Re: ATP example
Since hydrolysis represents the breaking of bonds in a reaction, energy and heat will for sure be released (as products are favored) leading to an exothermic reaction where the deltaH is negative.
- Fri Feb 28, 2020 11:26 am
- Forum: General Rate Laws
- Topic: Unique Rate
- Replies: 4
- Views: 342
Re: Unique Rate
The unique rate equation tells us that there is a ratio of products and reactants that is equal in terms of the rate in which the reaction is proceeding. Coefficients in the rate law relate to the coefficients of the balanced equation and shows the ratio between them.
- Fri Feb 28, 2020 11:21 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: intermediate
- Replies: 26
- Views: 1941
Re: intermediate
The intermediate in a series of reactions can be identified by seeing which element is both in the products of one reaction and reactants of another (it will cancel out as they are on opposite sides). Since it is not written in the overall reaction (as it is cancelled out), it is not included in the...
- Fri Feb 28, 2020 11:18 am
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Activation Energy
- Replies: 16
- Views: 1416
Re: Activation Energy
Activation energy simply put is the minimum amount of energy that is required to be inputted into a reaction to move the reaction forward. In the graph/diagram of energy vs. reaction process, the 'hump' in the graph represents the activation energy.
- Fri Feb 21, 2020 4:52 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: ln K equation
- Replies: 1
- Views: 158
ln K equation
I'm still confused as to how the equation lnk = -deltaH/RT + deltaS/R is related to a graph and what the graph shows us (extra)?
- Fri Feb 21, 2020 4:46 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Delta G
- Replies: 6
- Views: 337
Re: Delta G
Delta G (not) is the standard state of the Gibbs free energy of a compound, usually at 1atm and 25C (temperature). Delta G by itself depends on the compounds and non-STP conditions.
- Fri Feb 21, 2020 4:43 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: n in -nFE
- Replies: 14
- Views: 801
Re: n in -nFE
So if you were given an oxidation and reduction half equation, how do you know which coefficient (in front of the 'e-') to use? Do you add the moles of e- up or just select a number?
- Fri Feb 21, 2020 4:40 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Balancing redox reactions
- Replies: 2
- Views: 408
Balancing redox reactions
Hi! I'm still confused on how to decide which element in a multi-element compound you chose that is apparently oxidized or reduced?
- Wed Feb 12, 2020 1:55 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Entropy
- Replies: 4
- Views: 296
Re: Entropy
Increase in temperature yields a larger temperature change (where T2 and T1 is compared) and ther larger the temperature increase, the larger the deltaS (assuming the volume is not changing), as seen with the equation deltaS = nCln (t2/t1).
- Wed Feb 12, 2020 1:51 pm
- Forum: Calculating Work of Expansion
- Topic: Reversible and Isobaric
- Replies: 4
- Views: 303
Re: Reversible and Isobaric
Isobaric means that deltaP = 0, but doesn't say if the process is reversible or irreversible. Therefore, the only assumption one can make is that U = detaH - pdeltaV (as there is only one P value to plug in, usually external pressure).
- Wed Feb 12, 2020 1:46 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: ICE BOX Reverse ?
- Replies: 4
- Views: 348
Re: ICE BOX Reverse ?
If the concentration isn't given then most likely you must use other presented concentrations (and the ICE table) to calculate it. But the ratio of change could be 1 (the C part of the table) which would translate as just an X, but later the quadratic solution is plugged into these values to find co...
- Wed Feb 12, 2020 1:38 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Decreasing pressure
- Replies: 7
- Views: 542
Re: Decreasing pressure
A decrease in pressure corresponds to a higher volume (as pressure and volume are inversely proportional according to the ideal gas law, PV=nRT). So the reaction side with more moles of GAS is favored, as the higher moles of gas can occupy the larger value to return the reaction to equilibrium.
- Wed Feb 12, 2020 1:35 pm
- Forum: Ideal Gases
- Topic: R Constant
- Replies: 18
- Views: 1038
Re: R Constant
Correct, there are 3 different R values depending on the units that are presented to you, such as atm or torr. But they all are equivalent to each other (even though their units are somewhat different(.
- Wed Feb 12, 2020 1:33 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Reversible vs Irreversible
- Replies: 5
- Views: 400
Re: Reversible vs Irreversible
Correct, reversible is applied to the equation W = -pexdeltaV, when the change in p is constant. The other equation is used when the process is irreversible, and usually isothermal (deltaT = 0).
- Wed Feb 12, 2020 1:26 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: memorize
- Replies: 14
- Views: 763
Re: memorize
most entropies will be given to us, but it can be known that a perfect crystalline structure or molecule has a delta S of 0 J/K (though in reality, this is not possible, as seen with the 3rd law of thermodynamics)
- Wed Feb 12, 2020 1:24 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous
- Replies: 23
- Views: 1133
Re: Spontaneous
a negative delta G (corresponding to a positive delta S) correlates to a spontaneous reaction, while a positive is vice versa. If the delta G is 0, the system will have reached equilibrium, and the forward and backward rates are the same.
- Fri Feb 07, 2020 3:27 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: calculating entropy
- Replies: 4
- Views: 199
Re: calculating entropy
It represents the heat released by the system, or heat lost by the system. Therefore, it's not always -, depends on the pathway of heat transfer that determines the sign of q.
- Fri Feb 07, 2020 3:24 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy
- Replies: 2
- Views: 116
Re: Entropy
Residual entropy is calculated using the equation S=Kb * ln W --> in essence an entropy calculation based on the degeneracy of an entity. In general the higher the degeneracy the larger the S. W can be a whole # or the number of ways a molecule can be arranged.
- Fri Feb 07, 2020 3:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: q and w
- Replies: 10
- Views: 544
Re: q and w
If certain info is given, yes (but not necessarily the actual numerical value). For example, a -q can signify that heat is being lost from the system (transferred to another entity), and negative work can mean work is being done BY the system (work done ON the system signifies a positive w).
- Fri Feb 07, 2020 3:00 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Constant pressure
- Replies: 19
- Views: 626
Re: Constant pressure
Yes, constant external pressure, as it allows the system to change somewhat independent of the external environment. For example, in the equation for an irreversible expansion work, W = - P external * delta V. However, if it is a gas in a container, pressure of the gas may be determined through the ...
- Fri Feb 07, 2020 2:55 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Degeneracy
- Replies: 9
- Views: 320
Re: Degeneracy
For this course, it can be used to calculate entropy via the Boltzmann equation, that is S = Kb * ln W, where W is the degeneracy. In general larger molecules will have greater degeneracy. However, this equation has a lot of error associated with it, as its relying on a whole number and a defined va...
- Fri Feb 07, 2020 2:53 pm
- Forum: Calculating Work of Expansion
- Topic: Isothermal
- Replies: 17
- Views: 690
Re: Isothermal
Isothermal means constant temperature, or the change in temperature = 0. For the work equations, the irreversable expansion equation can be used, which is W = - P external * deltaV.
- Fri Feb 07, 2020 2:49 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Positive ∆S
- Replies: 5
- Views: 294
Re: Positive ∆S
a positive delta S can signify a spontaneous reaction, but to determine favor ability, Gibbs free energy equation must be used. But for now, positive delta S means particles are going towards disorder (more forms of degeneracy).
- Thu Jan 30, 2020 5:32 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed and Isolated
- Replies: 5
- Views: 222
Closed and Isolated
In most of the experiments, a closed experiment is described. However, is it ever possible to have a completely isolated system, as entropy exists and there can be very minute molecular interactions which allow very small amounts of heat, particularly, to enter or escape?
- Thu Jan 30, 2020 5:29 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Units for temperature?
- Replies: 11
- Views: 485
Re: Units for temperature?
You can use either Celsius Kelvin, but the units must be consistent throughout the equation, so the specific heat constant (for the specific material) must also be in the same units as the deltaT in the equation q=cmdeltaT.
- Thu Jan 30, 2020 5:26 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Strong/weak acids & bases
- Replies: 14
- Views: 894
Re: Strong/weak acids & bases
Yes, there's usually a pattern you can follow: anything with an OH- is usually a strong base (ex. KOH), and any compound preceded with an H and from the halogen group is usually a strong acid (HBr, HCl, etc.). But any compound with an NH3 is usually a weak acid, and others you can just memorize, lik...
- Thu Jan 30, 2020 5:24 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: H2O as a Gas
- Replies: 69
- Views: 6138
Re: H2O as a Gas
In the ICE table, gases and aqueous (which is dissolved in H2O) solutions are included, not solids or liquids. Therefore, H2O (almost always a gas or liquid) is included only if its not a liquid.
- Thu Jan 30, 2020 5:06 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Qv vs Qp
- Replies: 7
- Views: 129
Re: Qv vs Qp
Both represent heat energy of deltaH, but one is used when the volume is constant and the pressure changes (Qv) and the other is when the pressure is constant but the volume is changing (Qp).
- Fri Jan 24, 2020 2:17 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Calculating K
- Replies: 15
- Views: 692
Re: Calculating K
The idea of balancing a reaction is not associated with K; regardless, in order to solve a chemistry problem, the reaction should be balanced (with coefficients). When it is balanced, depending if the information is given for either pressure or concentration of the reactants AND products @ equilibri...
- Fri Jan 24, 2020 2:14 pm
- Forum: Ideal Gases
- Topic: Ideal Gases: Approximation
- Replies: 3
- Views: 224
Re: Ideal Gases: Approximation
Of course PV=nRT is labeled as the "Ideal Gas Law" - so no matter what condition of the experiment, some factors of the experiment will affect the calculations from the ideal gas law. For example, the temperature may fluctuate by +/- 0.5 C, and therefore a solid temperature may not be reco...
- Fri Jan 24, 2020 2:08 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: exothermic reactions
- Replies: 19
- Views: 1893
Re: exothermic reactions
It is part of LeChatlier's Principle: adding heat to a reaction will favor the other side of the reaction (wherever "heat" is added- reactant or product side). Exothermic reactions have "+heat" on the products side, therefore increasing the heat (or adding more heat) will favor t...
- Fri Jan 24, 2020 2:03 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Acids and Bases
- Replies: 6
- Views: 153
Re: Acids and Bases
I believe no, but the idea of a polyprotic acid is that it can donate more than one hydrogen atom in the equilibrium reaction (like 2+, 3+, etc.) and therefore will have different ionization levels and multiple Ka values.,
- Fri Jan 24, 2020 2:01 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Changes in Pressure
- Replies: 9
- Views: 343
Re: Changes in Pressure
Increasing the pressure will in turn decrease the volume of the container in which the specimens are contained: the side with less moles of gas favored as there are fewer molecules on that side of the reaction = smaller volume.
- Fri Jan 17, 2020 4:27 pm
- Forum: Student Social/Study Group
- Topic: Final Jitters
- Replies: 457
- Views: 333920
Re: Final Jitters
Always study like you are genuinely learning for fun and not for a test (but be serious). While taking the exam, don't see it as an exam, but as a homework problem thinking you are able to just spill out your ideas... you don't need to be perfect/cookie cutter when answering or thinking about the pr...
- Fri Jan 17, 2020 4:24 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5.33
- Replies: 3
- Views: 86
Re: 5.33
I believe because its the same ideology like adding an extra compound or atom that's different/not in the original equilibrium equation, will not change the K value or the reaction process. No shift occurs and it will be like the original equilibrium conditions.
- Fri Jan 17, 2020 4:22 pm
- Forum: Ideal Gases
- Topic: When to use this equation
- Replies: 14
- Views: 404
Re: When to use this equation
One use is when a compound or reaction is not in the STP state (standard 1atm, 25C), and you need to find a certain value to plug into a stoichiometric equation. More for specialized cases...
- Fri Jan 17, 2020 4:18 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Different types of acids/bases
- Replies: 3
- Views: 122
Different types of acids/bases
How do we know what type of acid/base a compound is? Such as bronstead-lowry, or arrhenius, or lewis acids/bases? And based on this categorization, do we treat it differently in a problem?
- Fri Jan 17, 2020 4:15 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Strong or weak acid?
- Replies: 5
- Views: 1125
Strong or weak acid?
How can you tell based on the chemical formula of a compound that it is a strong or weak base? Like I know my memory HCl and CH3COOH as strong and weak, respectively, but don't really know any others.