Search found 51 matches
- Sun Mar 14, 2021 7:21 pm
- Forum: Zero Order Reactions
- Topic: zero order
- Replies: 47
- Views: 1766
Re: zero order
Since a zero-order rate law will be k[A]^0, which is just k, that means that the rate does not depend on the concentration of the reactant(s).
- Sun Mar 14, 2021 7:13 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: k
- Replies: 36
- Views: 1463
Re: k
In an overall rate law, the concentrations will all be constant, so yes, the value of k will determine the speed of the reaction. Thus, a larger k will most definitely result in a faster reaction rate as opposed to a very small k value.
- Sun Mar 14, 2021 7:10 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Which form of equation
- Replies: 7
- Views: 418
Re: Which form of equation
I think ln k might be used a bit more because it is in linear form, which is easier to utilize and answer conceptual questions on. Both will give you the same answer to whatever the question may be, so feel free to use whichever one you feel more comfortable with.
- Sun Mar 14, 2021 7:07 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Effect of catalyst
- Replies: 22
- Views: 2189
Re: Effect of catalyst
Adding a catalyst will speed up a reaction by reducing its activation energy, thus resulting in a new, shorter pathway for the reactants to form products. However, since ΔH is a state function, it won't change in value when you speed up/slow down a reaction, because it doesn't depend on the pathway....
- Sun Mar 14, 2021 6:59 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: Catalyst
- Replies: 27
- Views: 1048
Re: Catalyst
Adding a catalyst will lower the activation energy, which both the forward and reverse reactions need to overcome. So, when the Ea is reduced as a result of the addition of a catalyst, then the forward and reverse reactions will both be overcoming a smaller value of Ea.
- Sun Mar 07, 2021 8:24 pm
- Forum: Balancing Redox Reactions
- Topic: How to Determine if a Reaction is in Basic or Acidic Solution?
- Replies: 53
- Views: 2849
Re: How to Determine if a Reaction is in Basic or Acidic Solution?
The question will explicitly ask you to calculate the redox reaction in either acidic or basic conditions. If it says acidic, then you know your final answer will have H+ ions, and if it is basic, then your answer will have OH- ions.
- Sun Mar 07, 2021 8:08 pm
- Forum: Zero Order Reactions
- Topic: Overall order of the reaction
- Replies: 45
- Views: 1738
Re: Overall order of the reaction
The overall order of a reaction is calculated by simply adding all of the orders for each individual reactant together.
- Sun Mar 07, 2021 7:33 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: nernst equation
- Replies: 20
- Views: 768
Re: nernst equation
The number of moles that is used in the Nernst equation is simply the number of electrons transferred in a reaction. This number is found by first writing out and balancing both half-reactions, and then when you add the half-reactions together, the number of electrons that you canceled out is the va...
- Sun Mar 07, 2021 7:29 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing Reactant
- Replies: 9
- Views: 599
Re: Oxidizing Reactant
In order for a reactant to be considered an oxidizing agent, it must gain electrons, or in other words, it must be reduced. By definition, oxidizing agents are the reactants that are being reduced, as they allow for another reactant in the chemical reaction to be oxidized.
- Sun Mar 07, 2021 7:25 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing Redox
- Replies: 16
- Views: 829
Re: Balancing Redox
In order to figure out how many electrons to add to a half-reaction, simply calculate the total charges on both the reactant side and product side. If you notice that one side is more positive than the other side, then you would add electrons to this side in order to make the charges on both sides e...
- Sun Mar 07, 2021 7:07 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: -d[R]/dT versus d[P]/dt
- Replies: 13
- Views: 857
Re: -d[R]/dT versus d[P]/dt
Assuming that the number of moles is the same for both the reactant and product, then yes, both of those values will be equal. Conceptually, this means that, in a reaction, as the amount of reactant decreases by some value, then the amount of product will increase by that same value in the same amou...
- Sun Feb 28, 2021 10:35 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: spontaneous reactions
- Replies: 3
- Views: 192
Re: spontaneous reactions
The reasoning that makes the most sense to me is just by looking at the equation ΔG⁰ = -nFE⁰. In this equation, we know that the value of n, or the number of moles of electrons transferred, is always going to be a positive number because you cannot have a negative transfer of moles of electrons. Als...
- Sun Feb 28, 2021 10:05 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: n in ∆G = -nFE
- Replies: 80
- Views: 3810
Re: n in ∆G = -nFE
In this equation, n refers to the number of moles of electrons that are transferred in a given chemical reaction. This value can be figured out when balancing your half reactions.
- Sun Feb 28, 2021 10:02 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: X electrode and Y electrode
- Replies: 4
- Views: 270
Re: X electrode and Y electrode
When the anode loses electrons, solid metal oxidizes into ions that then go into the solution. So, this electrode will decrease in size because it is losing some of its solid mass. On the other hand, the cathode gains electrons, which will reduce the ions already in the solution into solid metal. So...
- Sun Feb 28, 2021 9:41 pm
- Forum: Balancing Redox Reactions
- Topic: Determining which molecule is the oxidizing agent
- Replies: 49
- Views: 1758
Re: Determining which molecule is the oxidizing agent
Yes, the oxidizing agent is the substance that is being reduced, thus it is gaining electrons. Likewise, the reducing agent is the substance that is being oxidized, so it is losing electrons.
- Sun Feb 28, 2021 9:16 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: -d[R]/dT versus d[P]/dt
- Replies: 13
- Views: 857
Re: -d[R]/dT versus d[P]/dt
Assuming that the number of moles of the reactant is equivalent to moles of product, then the rate at which the concentration of the reactant is decreasing will be equal to the rate at which the concentration of the product is increasing. So yes, the magnitude of both values will be equal, the only ...
- Sun Feb 21, 2021 11:52 pm
- Forum: Balancing Redox Reactions
- Topic: Anode and Cathode
- Replies: 11
- Views: 482
Re: Anode and Cathode
Yes, the anode is always the side of oxidation, and the cathode is always the side of reduction. In high school, I remember learning a mnemonic that helped me remember this - "An Ox; Red Cat" (Anode: Oxidation; Reduction: Cathode).
- Sun Feb 21, 2021 11:47 pm
- Forum: Balancing Redox Reactions
- Topic: Easy way to remember reduction/oxidazing agents?
- Replies: 10
- Views: 1070
Re: Easy way to remember reduction/oxidazing agents?
In order to figure out which substance is being reduced and which is being oxidized, you really only need to look at its oxidation number. If the oxidation number increases (gets more positive), that means the substance has lost one or more of its electrons, so it is oxidized. If the oxidation numbe...
- Sun Feb 21, 2021 11:41 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing vs Reducing
- Replies: 55
- Views: 2249
Re: Oxidizing vs Reducing
OIL RIG is a good mnemonic for remembering what happens to electrons for each process: "Oxidation is Loss, Reduction is Gain". In order to figure out the type of agent a substance is, it is basically just the opposite of what you would expect. For example, an oxidizing agent is a substance...
- Sun Feb 21, 2021 11:37 pm
- Forum: Balancing Redox Reactions
- Topic: "Leo" Oxidation Numbers
- Replies: 26
- Views: 1059
Re: "Leo" Oxidation Numbers
LEO is not a scientific term; it's basically just an acronym for "Lose Electrons- Oxidation". It's meant to help us remember that the process of oxidation refers to when a substance is losing one or more of its electrons during a chemical reaction.
- Sun Feb 21, 2021 11:34 pm
- Forum: Balancing Redox Reactions
- Topic: Reducing vs oxidizing agents
- Replies: 16
- Views: 768
Re: Reducing vs oxidizing agents
Oxidizing agents are the substances that are being reduced, so they gain electrons. Reducing agents are the ones being oxidized, so they lose electrons.
- Sun Feb 14, 2021 11:57 pm
- Forum: Calculating Work of Expansion
- Topic: Ideal gas constant
- Replies: 9
- Views: 769
Re: Ideal gas constant
In order to figure out which gas constant to use from our equation sheet, you really only need to pay attention to which units are being given in the question. If it gives you some value of pressure in joules, use 8.314, and if the pressure is given in atm, then use 0.08206. You could also convert b...
- Sun Feb 14, 2021 11:53 pm
- Forum: Calculating Work of Expansion
- Topic: Sign of work
- Replies: 25
- Views: 857
Re: Sign of work
I believe that when work is done on the system, our value for w will be positive. Likewise, when work is being done by the system, our w-value will be negative. Essentially, you really just need to look at the delta V value to figure out which sign to use, assuming a positive value for pressure. If ...
- Sun Feb 14, 2021 11:45 pm
- Forum: Calculating Work of Expansion
- Topic: Work Done on System?
- Replies: 12
- Views: 512
Re: Work Done on System?
Based on Professor Lavelle's examples in class, when a system is expanding, or increasing in volume, that means that work is being done by the system and your w-value is negative. Essentially, when volume is increasing, that means your delta V value is positive; so, the equation w = -P*deltaV would ...
- Sun Feb 14, 2021 11:39 pm
- Forum: Calculating Work of Expansion
- Topic: negative vs positive work
- Replies: 21
- Views: 889
Re: negative vs positive work
Work is negative when the system is expanding, meaning that the system is doing work in order to expand the volume of the system. Thus, work is positive when the system is compressing, meaning that work is being done on the system, rather than by the system.
- Sun Feb 14, 2021 11:36 pm
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: isochoric / isometric
- Replies: 9
- Views: 556
Re: isochoric / isometric
Isochoric refers to a reaction in which volume remains constant. In other words, your delta V value will be zero. I don't remember going over isometric in class though so I would assume we don't need to know how to apply that.
- Sat Feb 06, 2021 8:04 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Work
- Replies: 39
- Views: 1387
Re: Work
When the amount of work is a negative value, that basically means that the system is doing work on its surroundings. The energy that the system uses in order to do work on its surroundings will thus be negative, as that amount of energy is leaving the system.
- Sat Feb 06, 2021 7:58 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: deltaU
- Replies: 29
- Views: 784
Re: deltaU
Delta U is the change in internal energy in a system. It can be calculated by adding the heat absorbed into or released by the system with the work done on or by the system.
- Sat Feb 06, 2021 7:54 pm
- 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: w
- Replies: 12
- Views: 748
Re: w
You would only need to apply Avogadro's number if the question asks you to find the degeneracy of a mole of the given substance.
- Sat Feb 06, 2021 7:48 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Key points of First Law
- Replies: 8
- Views: 190
Re: Key points of First Law
The first law of thermodynamics basically states that energy cannot be created or destroyed, rather it can be transferred from the system to its surroundings and vice versa. The equation associated with this law is the change in internal energy, delta U, = q + w.
- Sat Feb 06, 2021 7:40 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: How to know the sign for work
- Replies: 26
- Views: 895
Re: How to know the sign for work
Essentially, if work is being done on the system, that means you will have a positive w, because the surroundings are performing some amount of work on the system. On the other hand, if work is being done by the system, that means you will have a negative w, because the system is losing some amount ...
- Sun Jan 31, 2021 11:26 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: closed system
- Replies: 43
- Views: 1468
Re: closed system
By definition, a closed system does not allow for the exchange of matter between the system and its surroundings. This makes sense because the system will be sealed, and therefore you should not expect any matter to leave the system, or enter the system from its surroundings.
- Sun Jan 31, 2021 11:05 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: R Constant
- Replies: 91
- Views: 5216
Re: R Constant
Picking the right R constant to use is as easy as identifying the units that are given in the question. Essentially, you want most of your units in the PV=nRT equation to cancel out, leaving you with just the unit for whatever the question is asking for. So, always pick the R constant that contains ...
- Sun Jan 31, 2021 10:49 pm
- Forum: Calculating Work of Expansion
- Topic: why expanding volume has negative work
- Replies: 6
- Views: 352
Re: why expanding volume has negative work
When the volume of the container expands (for example, a piston is being pushed up in a closed system), it requires work to be done on the system. And, since the system is losing energy while doing the work of expansion, we would therefore see a negative sign.
- Sun Jan 31, 2021 10:27 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Sapling Week 3 #5
- Replies: 7
- Views: 349
Re: Sapling Week 3 #5
By the looks of it, I think you may be canceling out similar-looking substances that are existing in different states. For example, HCl appears in equations 1, 2, and 3, but some HCl is in the aqueous state and some of it is in the gaseous state. By multiplying the third equation by 3, as you mentio...
- Sun Jan 31, 2021 10:20 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: endothermic/exothermic Q and K
- Replies: 16
- Views: 2000
Re: endothermic/exothermic Q and K
If the delta H of a system is positive, that means that heat is being added into the system. If delta H is negative, that means that heat is being removed from the system. When temperature is increased in a system, this means that heat is being added, so the system will shift right for an endothermi...
- Sun Jan 24, 2021 8:56 pm
- Forum: Phase Changes & Related Calculations
- Topic: Steam
- Replies: 33
- Views: 1798
Re: Steam
The reason why steam causes more severe burns when it comes into contact with your hand than water is that there is a larger amount of energy being released from the steam onto your hand. Both are at the same temperature, but steam has a larger amount of energy because it undergoes the phase change ...
- Sun Jan 24, 2021 8:30 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Changes
- Replies: 18
- Views: 537
Re: Phase Changes
During a phase change, the temperature remains the same, but the change in enthalpy will either increase or decrease. For example, when going from liquid water to gaseous steam, the temperature will remain at 100 degrees C during the phase change, but the enthalpy will still increase since heat is r...
- Sun Jan 24, 2021 8:24 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: pKa
- Replies: 14
- Views: 461
Re: pKa
The relationship between those two things is that they are the exact same. Calculating -log(Ka) will actually just give you the value of pKa.
- Sun Jan 24, 2021 7:54 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess Law
- Replies: 10
- Views: 1611
Re: Hess Law
When you flip a reaction, its delta H value will change signs. When you multiply a reaction by a number, multiply the delta H value by that same number. After doing all the necessary adjustments, add up all the delta H values together.
- Sun Jan 24, 2021 7:44 pm
- Forum: Phase Changes & Related Calculations
- Topic: Endothermic v. Exothermic
- Replies: 139
- Views: 10240
Re: Endothermic v. Exothermic
Yep, endothermic reactions will always have a positive delta H, because this type of reaction takes in heat, thus it would have a positive change in enthalpy. On the other hand, exothermic reactions will have a negative delta H because you lose heat while the reaction is taking place, thus resulting...
- Sun Jan 17, 2021 6:36 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Q > K, Q< K
- Replies: 25
- Views: 762
Re: Q > K, Q< K
When Q > K, that means that the products are being produced more than they would if the reaction were at equilibrium. In this case, the reaction would want to make more reactants to compensate, thus causing the reaction to favor the reactants (shift to the left). When Q < K, that means that the prod...
- Sun Jan 17, 2021 6:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Week 1 Sapling 3
- Replies: 11
- Views: 460
Re: Week 1 Sapling 3
You could use the quadratic formula, but this question was especially nice because if you square root both sides, you get rid of any x^2 expressions, which would make it a lot easier to find the x-value in this case. But, if you decided to use the quadratic formula, you should reach the same value f...
- Sun Jan 17, 2021 6:22 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Using the ICE table
- Replies: 36
- Views: 1314
Re: Using the ICE table
That's correct. The main purpose of ICE tables is to find amounts of reactants and products at equilibrium when given initial amounts, which can be in either concentration or pressure, based on what the question gives you / is asking for.
- Sun Jan 17, 2021 6:08 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Ice Box Method
- Replies: 14
- Views: 425
Re: Ice Box Method
If we are looking at a forward reaction, then the change in reactant concentrations will be negative, and the change in product concentrations will be positive. When a question gives us initial concentrations for reactants, that means that when the reaction reaches equilibrium, some amount of reacta...
- Sun Jan 17, 2021 5:51 pm
- Forum: Ideal Gases
- Topic: Inverse Kc [ENDORSED]
- Replies: 41
- Views: 1900
Re: Inverse Kc [ENDORSED]
We would need to find the inverse of Kc (1/Kc) whenever we are asked to find the equilibrium constant of the reverse reaction.
- Sun Jan 10, 2021 6:35 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: reaction quotient Q vs. equilibrium constant K
- Replies: 11
- Views: 323
Re: reaction quotient Q vs. equilibrium constant K
Essentially, the value of Q just refers to the ratio of products to reactants when the reaction is not at equilibrium. The value of K, which will never change for a particular reaction, refers to the ratio of products to reactants when that reaction is at equilibrium. Thus, when we compare the value...
- Sun Jan 10, 2021 6:14 pm
- Forum: Ideal Gases
- Topic: PV=nRT and concentration
- Replies: 27
- Views: 1403
Re: PV=nRT and concentration
Molarity is calculated by dividing the moles of a particular substance by the volume of the reaction vessel. When looking at the ideal gas law, n=moles and V=volume, so n/V will give us moles/volume, aka the molarity of that substance.
- Sun Jan 10, 2021 6:03 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Calculating Equilibrium Concentrations
- Replies: 10
- Views: 386
Re: Calculating Equilibrium Concentrations
That's correct. The purpose of using ICE tables is to find concentrations of reactants/products at equilibrium so that we can solve for K (if the question asks to solve for K). And, as we already know, solids and liquids serve no purpose when calculating K, so they can be left off the ICE table.
- Sun Jan 10, 2021 5:48 pm
- Forum: Ideal Gases
- Topic: value of R
- Replies: 24
- Views: 972
Re: value of R
In order to figure out which correct R value to use, you would simply look at the units given within the question. Technically, you can use any R value as long as you convert the given units in the question to match the units on the R value that you choose, but there's no reason to go through all th...
- Fri Jan 08, 2021 11:24 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Increasing Pressure by Adding an Inert Gas
- Replies: 6
- Views: 752
Re: Increasing Pressure by Adding an Inert Gas
Hi! So here's my understanding of this particular topic. When we add an inert gas to a reaction vessel, we are not changing the actual volume of the vessel at all. In your post, you wrote that "adding a gas would increase the pressure, which would decrease the volume". However, changing th...