Search found 46 matches
- Sun Mar 08, 2020 9:08 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: pre-exponential factor
- Replies: 3
- Views: 231
Re: pre-exponential factor
It is the frequency of collisions.
- Sun Mar 08, 2020 9:07 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Catalysts
- Replies: 28
- Views: 1623
Re: Catalysts
Catalysts reduce the activation energy.
- Sun Mar 08, 2020 9:03 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Where do we find the values for A?
- Replies: 5
- Views: 469
Re: Where do we find the values for A?
It's pretty much like finding a missing variable for any standard equation. As long as you have the temperature, activation energy, gas constant, and gas constant, you can solve for A. A is the frequency of collisions.
- Sun Mar 08, 2020 8:56 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Intermediate Species
- Replies: 9
- Views: 659
Re: Intermediate Species
An intermediate species is not part of the overall reaction equation, but it does play a role in the mechanisms of it. It is formed and consumed in the middle of the reaction.
- Sun Mar 08, 2020 8:44 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Arrhenius Equation
- Replies: 4
- Views: 335
Re: Arrhenius Equation
With factors like temperature, frequency of collisions, catalyst presence, and activation energy, you can determine the rate of reaction.
- Sun Mar 08, 2020 8:11 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: A in the Arrhenius Equation
- Replies: 3
- Views: 253
Re: A in the Arrhenius Equation
A stands for the frequency of collisions.
- Sun Mar 01, 2020 5:53 pm
- Forum: General Rate Laws
- Topic: Reaction Rates
- Replies: 5
- Views: 354
Re: Reaction Rates
It's almost like slowing down while running. Although you have slowed down, you are still moving forward, you wouldn't be going backwards. Similar to this, reaction rates are always positive because in a forward reaction, the reaction does not go backwards.
- Sun Mar 01, 2020 5:49 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Diamond
- Replies: 6
- Views: 426
Diamond
Why is it that diamond is kinetically stable and controlled with respect to graphite if the reaction for this to happens takes so long under STP? Is it because it is quicker, relative to graphite?
- Sun Mar 01, 2020 5:32 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: how can you tell
- Replies: 11
- Views: 746
Re: how can you tell
Thermodynamic-controlled reactions are usually long, while kinetic-controlled reactions are relatively quick.
- Sun Mar 01, 2020 5:21 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: intermediate
- Replies: 26
- Views: 1940
Re: intermediate
Intermediates are produced then consumed, during some part of the reaction. It cannot exist in rate law because they are not a part of the overall equation.
- Sun Mar 01, 2020 5:17 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: Activation Energy
- Replies: 16
- Views: 1416
Re: Activation Energy
Activation energy is the amount of energy needed to turn reactants to products. This is depicted on a diagram with the highest hump.
- Sat Feb 22, 2020 10:08 pm
- Forum: Balancing Redox Reactions
- Topic: Basic conditions
- Replies: 6
- Views: 385
Re: Basic conditions
In a basic solution, you would use hydroxide (OH-) to balance out the hydrogens (H). This is different from acidic solutions, in which you would use (H3O+) to balance out any hydrogens (H).
- Sat Feb 22, 2020 9:59 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: property of E
- Replies: 6
- Views: 396
Re: property of E
E is an intensive property, so it does not depend on the amount of times the reaction occurs. The voltage difference will remain the same, because of this.
- Sat Feb 22, 2020 9:58 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Standard Cell Potentials
- Replies: 4
- Views: 289
Re: Standard Cell Potentials
The anode is typically on the left, while the cathode is on the right. It would be the potential on the right (cathode) minus the potential on the left (anode).
- Sat Feb 22, 2020 9:56 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 10
- Views: 594
Re: Salt Bridge
The salt bridge is needed to allow ions to flow freely, which will free any charge buildup. It is important for this to occur, because it allows the flow of electrons to be maintained.
- Sat Feb 22, 2020 8:43 pm
- Forum: Balancing Redox Reactions
- Topic: Redox in Acid/ Basic Solutions
- Replies: 8
- Views: 496
Re: Redox in Acid/ Basic Solutions
The main difference comes from how you balance the equation. For basic solutions, you would balance out the equation by adding hydroxide ions (OH-). For acidic solutions, you would balance out the equation by adding protons (H+).
- Sun Feb 16, 2020 3:28 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Equilibrium
- Replies: 5
- Views: 231
Re: Equilibrium
Delta G is 0 at equilibrium, but delta S and delta H could be nonzero in order for delta G to be 0. This is as long as the equation results in 0.
- Sun Feb 16, 2020 3:27 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Equilibrium
- Replies: 15
- Views: 778
Re: Equilibrium
Neither reverse nor forward reaction is favored at equilibrium, so at delta G naught 0, the reaction is neither spontaneous nor non-spontaneous. This would mean neither reaction is favored, so it would be at equilibrium.
- Sun Feb 16, 2020 3:23 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs Free energy concept
- Replies: 16
- Views: 782
Re: Gibbs Free energy concept
Gibbs Free Energy is the amount of energy available to do work. A negative value would indicate spontaneity. A positive value would indicate non-spontaneity.
- Sun Feb 16, 2020 3:16 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Why are exothermic reactions generally spontaneous?
- Replies: 16
- Views: 1114
Re: Why are exothermic reactions generally spontaneous?
This is mainly because a reaction that is spontaneous would not require heat input. They release energy upon completion.
- Sun Feb 16, 2020 3:13 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: maximum work
- Replies: 5
- Views: 392
Re: maximum work
Maximum work refers to work done by a system during a reversible reaction. As such, maximum work, when none is lost as heat, would be theoretical.
- Sun Feb 09, 2020 12:45 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Molar Entropy
- Replies: 4
- Views: 255
Re: Molar Entropy
Molar entropy is the entropy content of 1 mole of a substance. Entropy is the degree of disorder, or the energy unavailable for doing work.
- Sun Feb 09, 2020 12:43 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Energy Change
- Replies: 4
- Views: 184
Re: Energy Change
A spontaneous reaction is favorable, and this occurs when deltaG is negative. It will proceed forward because of this.
- Sun Feb 09, 2020 12:42 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Spontaneous Reaction
- Replies: 8
- Views: 367
Re: Spontaneous Reaction
Yes, when the deltaG is negative, this gives a spontaneous and more favorable reaction.
- Sun Feb 09, 2020 12:40 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: gibbs free energy of formation
- Replies: 3
- Views: 149
Re: gibbs free energy of formation
If Gibbs Free Energy is negative, it is more stable because it refers to spontaneity of a reaction. Spontaneous reactions tend to yield more stable products as they are not "forced" to undergo a reaction, in contrast to a non-spontaneous reaction.
- Sun Feb 09, 2020 12:36 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: Gibbs free energy
- Replies: 4
- Views: 222
Re: Gibbs free energy
Gibbs free energy is the energy in a chemical reaction that can be used to do work. Since enthalpy is the total heat content of a system, you would subtract entropy, which is the unavailable energy that is used for work, with temperature. This gives us the energy that can be used for work.
- Sun Feb 02, 2020 6:16 pm
- Forum: Calculating Work of Expansion
- Topic: Work positive or negative
- Replies: 5
- Views: 171
Re: Work positive or negative
If the system is doing work, you would have a negative value because energy is being used. This is because the system loses something, energy, resulting in the negative value we see. If work is being done on the system, you would receive a positive value because the energy is directed towards the sy...
- Sun Feb 02, 2020 6:14 pm
- Forum: Calculating Work of Expansion
- Topic: Reversible Process
- Replies: 2
- Views: 98
Re: Reversible Process
Yes, a constant pressure accounts for an irreversible reaction. A reversible reaction, in that case, could have a non-constant pressure.
- Sun Feb 02, 2020 5:50 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Pressure in an open beaker
- Replies: 12
- Views: 734
Re: Pressure in an open beaker
An open beaker system allows the exchange of pressure between its surroundings and the system. Since the atmosphere is relatively large, the pressure of the beaker will not have an effect on it, almost like a drop-in-the-bucket type deal. We can then infer a constant pressure because of this.
- Sun Feb 02, 2020 5:47 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Closed vs isolated systems
- Replies: 24
- Views: 813
Re: Closed vs isolated systems
A closed system cannot exchange matter with its surroundings, but it can exchange energy. An isolated system cannot exchange matter or energy.
- Sun Feb 02, 2020 5:42 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: entropy?
- Replies: 4
- Views: 199
Re: entropy?
Entropy is a degree of disorder. We need both the change in entropy and the change in internal energy to be able to fully describe how a system will change. We need entropy because its degree would allow us to determine how spontaneous something is.
- Sun Jan 26, 2020 4:41 pm
- Forum: Phase Changes & Related Calculations
- Topic: phase changes
- Replies: 6
- Views: 232
Re: phase changes
The exothermic phase changes we are currently discussing are condensation, freezing, and deposition. The endothermic phase changes are vaporization, melting, and sublimation.
- Sun Jan 26, 2020 4:35 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase changes: endothermic vs exothermic
- Replies: 12
- Views: 1121
Re: Phase changes: endothermic vs exothermic
Yes, it is important to note that the reverse of those reactions are condensation, freezing, and deposition, respectively. Condensation, freezing, and deposition are bond forming, which is why they would be exothermic. Bond breaking, on the other hand, would include vaporization, melting, and sublim...
- Sun Jan 26, 2020 4:31 pm
- Forum: Phase Changes & Related Calculations
- Topic: State property
- Replies: 6
- Views: 262
Re: State property
A state property "is not dependent on path taken to obtain that state." Examples would include E(nergy), P(ressure), V(olume), T(emperature), Density, and Heat Capacity.
- Sun Jan 26, 2020 4:28 pm
- Forum: Phase Changes & Related Calculations
- Topic: What is a state function?
- Replies: 3
- Views: 153
What is a state function?
So from the lecture, there is a point that enthalpy is a state function, therefore it must be additive, but I'm not quite sure what a state function is. Can anyone explain?
- Sun Jan 26, 2020 4:20 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Lewis Structures Method 2
- Replies: 6
- Views: 147
Re: Lewis Structures Method 2
It is useful to draw out the lewis structures when attempting to visualize the forming and breaking of bonds in the products or reactants. It's not necessary, but it does give you some peace of mind to justify reasoning.
- Sun Jan 19, 2020 1:25 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Difference between K and Q?
- Replies: 11
- Views: 514
Re: Difference between K and Q?
They look very similar because the only difference between the two constants is when you should use them. You use K when the reaction is at equilibrium, and you use Q at any stage of the reaction. You can compare the two constants to determine which way the reaction is shifting.
- Sun Jan 19, 2020 1:19 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Acids and Bases Ice Box
- Replies: 5
- Views: 132
Re: Acids and Bases Ice Box
Alison Trinh 1E wrote:What is the purpose of an ICE Box?
It is a step-by-step procedure that is used to put concentrations in terms of x, which you can then solve using approximation or the quadratic formula. You can then find a various amount of information with x such as KA, pH, etc.
- Sun Jan 19, 2020 1:10 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Pressure
- Replies: 5
- Views: 213
Re: Pressure
It depends entirely on the number of moles on the different sides of the equation. An increase in pressure will favor the side with less gaseous moles.
- Sun Jan 19, 2020 1:05 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5J.5
- Replies: 2
- Views: 88
Re: 5J.5
I got the same answer as well. There was no change for d because both sides of the equation have the same number of gaseous moles.
- Sun Jan 19, 2020 1:00 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5% rule
- Replies: 10
- Views: 434
Re: 5% rule
The 5% rule generally applies to approximation when trying to find x, after performing an ICE table. Instead of using the quadratic formula, you can disregard x relative to the initial if what you get from the approximation is less than 5% of the initial value. The procedure to finding that value is...
- Sat Jan 11, 2020 4:14 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Reaction quotient
- Replies: 8
- Views: 360
Re: Reaction quotient
Q is the reaction quotient, which can be used anytime during a reaction dealing with gases. K is the equilibrium constant, so it can only be calculated once the reaction is at equilibrium.
- Sat Jan 11, 2020 4:05 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K values
- Replies: 4
- Views: 142
Re: K values
If K=1, that would mean the amount of products and reactants are equal. This is rare because the forward and reverse reactions would have to reach equilibrium at this intermediate value.
- Sat Jan 11, 2020 4:00 pm
- Forum: Ideal Gases
- Topic: Solids and liquids [ENDORSED]
- Replies: 6
- Views: 264
Re: Solids and liquids [ENDORSED]
Since liquids are considered a pure substance, the molar concentration would not change in a reaction. We do not consider them in the equilibrium constant because of this.
- Sat Jan 11, 2020 3:56 pm
- Forum: Ideal Gases
- Topic: R in PV=nRT
- Replies: 34
- Views: 5845
Re: R in PV=nRT
R refers to the gas constant which depends on the units you are using for your equation.
- Sat Jan 11, 2020 3:50 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5G.1 [ENDORSED]
- Replies: 4
- Views: 170
Re: 5G.1 [ENDORSED]
So for this exercise, you have to determine which statements are true or false. If I am correct, you are referring to part c of 5G.1. The statement that if you start with a higher pressure of reactant, the equilibrium will be larger, is false.