Search found 54 matches
- Fri Mar 13, 2020 3:12 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Arrhenius Equation
- Replies: 8
- Views: 599
Re: Arrhenius Equation
k=A*e^-Ea/RT This formula helps determine the temperature dependence of reaction rates. k is the reaction rate of the reaction. A is a pre-exponential factor and has to do with the collision of the molecule (and if it is properly oriented when it collides in order to react) Ea is the activation ener...
- Fri Mar 13, 2020 3:08 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: A- pre-exponential factor
- Replies: 2
- Views: 326
Re: A- pre-exponential factor
A is found by the arrhenius equation k=Ae^-Ea/RT. If you are asked to find A, you will be provided the information to plug in the values for all other variables in the equation. So basically, you'll end up dividing k by the term e^-Ea/RT (or the subsequent number value you get) to isolate A on one s...
- Fri Mar 13, 2020 3:05 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Arrhenius equation
- Replies: 2
- Views: 270
Re: Arrhenius equation
The value of Ea will either be given or you will be able to find it by plugging in the values of the rest of the variables in the arrhenius equation.
- Fri Mar 13, 2020 2:57 pm
- Forum: First Order Reactions
- Topic: Half Life
- Replies: 13
- Views: 860
Re: Half Life
Half-lives in general are also useful ways of measuring how old a substance is. Real-world applications include figuring out how old a fossil is or how long it will take a substance to decay.
- Fri Mar 13, 2020 2:41 pm
- Forum: First Order Reactions
- Topic: size
- Replies: 6
- Views: 525
Re: size
I believe only the stoichiometric coefficient of the reaction would impact the rate (ie- if 2 or 1 or 3 molecules are colliding, etc.)
- Sun Mar 08, 2020 12:54 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: linear plots
- Replies: 7
- Views: 568
Re: linear plots
Yea I think the important part is knowing what to label the axes for each order. Beyond that just draw a linear function; I don't think we'd be expected to use data and graph it specifically.
- Sun Mar 08, 2020 12:47 pm
- Forum: Reaction Mechanisms, Reaction Profiles
- Topic: intermediates
- Replies: 5
- Views: 407
Re: intermediates
Lavelle said we will never be asked to determine what the intermediates of a reaction are. We'll be provided the intermediates and enough information to balance the reactions/determine which intermediate reaction is accurate, etc.
- Sun Mar 08, 2020 12:46 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Equation
- Replies: 9
- Views: 1308
Re: Equation
Madeline Motamedi 4I wrote:Yeah I believe for our purpose we are usually assuming A is just 1.
Does this mean that A is always a whole number?
- Sun Mar 08, 2020 12:41 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: activation energy/ energy barrier
- Replies: 6
- Views: 469
Re: activation energy/ energy barrier
Graphically, activation energy is the hump in between the reactants and products that must be overcome in order for the reaction to proceed. Both exo and endo reactions have an activation energy, and catalysts help to minimize this activation energy. It is a numerical value, yes.
- Sun Mar 08, 2020 12:34 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: concentration cells
- Replies: 5
- Views: 427
concentration cells
Why does a difference in concentrations cause a flow of electrons? And why do the electrons flow from low concentration to high concentration? Is there still a redox reaction taking place? Or is it something else?
- Sat Feb 29, 2020 4:32 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidizing/reducing agent
- Replies: 18
- Views: 1155
Re: Oxidizing/reducing agent
An oxidizing agent is one that causes a substance to be oxidized (meaning that the oxidizing agent is reduced).
The reducing agent causes a substance (the other element/molecule in the reaction) to be reduced (so the reducing agent is oxidized).
The reducing agent causes a substance (the other element/molecule in the reaction) to be reduced (so the reducing agent is oxidized).
- Sat Feb 29, 2020 4:28 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Problem 6L.7a: Cell Diagram Notation
- Replies: 1
- Views: 187
Re: Problem 6L.7a: Cell Diagram Notation
The way I took this answer was that the Ag(s) on the left is serving as the metal on the anode side that conducts electricity for electron flow. Since there is no solid pure metal on the left side, the silver is necessary to conduct electricity (much like Pt does). This is why it's separated by a |
- Fri Feb 28, 2020 11:24 am
- Forum: Balancing Redox Reactions
- Topic: Writing half reactions
- Replies: 9
- Views: 697
Writing half reactions
When writing half reactions to balance a redox reaction, does it matter what you put as the reactants or products? In the textbook, they always put the oxidized molecule on the left and reduced on the right (they do the same for cell diagram). Does it matter? Is it proper to keep oxidized on the lef...
- Thu Feb 27, 2020 6:49 pm
- Forum: Balancing Redox Reactions
- Topic: 6K. 5a)
- Replies: 5
- Views: 409
Re: 6K. 5a)
Section 6K has a useful table that explains how to balance reactions in acidic and basic solutions. When it comes to balancing a reaction in a basic solution, you balance oxygen first with water on either side and then to balance hydrogens, you add water to the side that needs more hydrogens and ad...
- Thu Feb 27, 2020 6:45 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Potentials on Test 2
- Replies: 3
- Views: 265
Re: Cell Potentials on Test 2
I'm assuming that we'll be given any cell potential not values we need and from that we can calculate the cell potential. Any quantitative value will either be provided or we'll be given the equation needed to calculate it.
- Sat Feb 22, 2020 9:57 pm
- Forum: Balancing Redox Reactions
- Topic: Redox in Acid/ Basic Solutions
- Replies: 8
- Views: 547
Re: Redox in Acid/ Basic Solutions
For acidic reactions, we have to add water to the reduction and oxidation reactions to balance out the oxygens. Do we have to add water to balance oxygens in basic conditions, or do we only add OH- to balance oxygen molecules? You use water to balance in both acidic and basic solutions. In both, yo...
- Sat Feb 22, 2020 9:54 pm
- Forum: Balancing Redox Reactions
- Topic: Oxidation Numbers
- Replies: 9
- Views: 665
Re: Oxidation Numbers
You're best off memorizing the main rules (ex: O2 is always -2 for this class, group 1 are +1, etc.) When looking at a compound, first look at the elements that have oxidation number rules and figure out what the oxidation number of a single atom would be. Then multiply that by any subscript or stoi...
- Sat Feb 22, 2020 9:42 pm
- Forum: Balancing Redox Reactions
- Topic: 6K. 5a)
- Replies: 5
- Views: 409
Re: 6K. 5a)
Section 6K has a useful table that explains how to balance reactions in acidic and basic solutions. When it comes to balancing a reaction in a basic solution, you balance oxygen first with water on either side and then to balance hydrogens, you add water to the side that needs more hydrogens and add...
- Sat Feb 22, 2020 4:26 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Delta G and delta Gr
- Replies: 3
- Views: 439
Re: Delta G and delta Gr
I believe the subscript r just stands for reaction, so if you're using r then you're accounting for the stoichiometric coefficients (ie moles) within the reaction. I don't think that you need to worry much about which of the two equations to pick, I think the r is more symbolic and reminding you wha...
- Sat Feb 22, 2020 4:22 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: E° as state function?
- Replies: 3
- Views: 344
Re: E° as state function?
Cell potential is not a state function. Cathode and anode has to do with a single cell at a particular point in time so combining their values gives the cell potential by definition. However, you can't simply find a new cell potential by subtracting some initial value from a final value, so it is no...
- Sat Feb 15, 2020 6:09 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: When to use internal energy equation
- Replies: 3
- Views: 334
Re: When to use internal energy equation
This equation is related to the internal energy of an ideal gas and the heat capacities at constant pressure and volume for various gas molecules. I don't think we necessarily need to use it for this class.
- Sat Feb 15, 2020 6:08 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: delta U= delta H
- Replies: 21
- Views: 1625
Re: delta U= delta H
When there is a constant volume or pressure, no expansion or compression work is being done by the system so w=0. When heat is at constant pressure, it equals the enthalpy change, so at constant pressure, delta U is equal to delta H.
- Sat Feb 15, 2020 6:05 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Internal energy of ideal gas
- Replies: 6
- Views: 521
Re: Internal energy of ideal gas
Why is the change in internal energy of an ideal gas 0 at constant temperature? What about a constant temperature and it being an ideal gas makes the internal energy not change?
- Sat Feb 15, 2020 6:03 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 8
- Views: 605
Re: Delta U
It's important to remember than delta U is the change in internal energy rather than just the internal energy of a system. It's a state function that looks at how the internal energy of a system changes over the course of a process (if a system releases or absorbs energy).
- Fri Feb 14, 2020 8:58 am
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: using the first law
- Replies: 3
- Views: 286
Re: using the first law
With constant pressure or volume, there is no expansion or compression work being done so w can be ignored. You don't really ignore q unless it's specifically stated that there is no heat transfer.
- Thu Feb 13, 2020 10:33 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Why is delta U a state function?
- Replies: 4
- Views: 377
Re: Why is delta U a state function?
I view state functions as part of the definition of a variable- what it represents. We just defined internal energy as the inner store of kinetic and potential energy of a system which only cares about the current or previous states and not the paths. So yes, it just has to do with the definition of...
- Thu Feb 13, 2020 7:13 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Delta U
- Replies: 5
- Views: 396
Re: Delta U
When a system is isothermal, it means that the temperature is constant so only work (expansion/compression) is considered. Internal energy is not 0 because a system is isothermal; it's 0 if the system is isolated. If a system is isolated, none of its energy is transferred to the surroundings, making...
- Mon Feb 03, 2020 12:55 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Double bonds
- Replies: 4
- Views: 215
Re: Double bonds
(at least in this class, as far as I know) A double bond isn't 2 separate bonds but rather 1 stronger bond. So when you break a single double bond, you're breaking that entire bond. There aren't 2 bonds within a double bond.
- Mon Feb 03, 2020 12:54 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Energy of a system
- Replies: 5
- Views: 381
Re: Energy of a system
In an exothermic reaction, the system loses energy in the form of heat, so the value of delta H and U is negative. When the system undergoes an endothermic reaction, it gains energy in the form of heat, so delta H and U is positive.
- Mon Feb 03, 2020 12:53 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: q vs H
- Replies: 9
- Views: 500
Re: q vs H
Jamie Lee 1F wrote:GFolk_1D wrote:Are deltaH and q interchangeable?
At constant pressure, qp = deltaH. Otherwise, they are not interchangeable.
How do delta H and q relate if pressure isn't constant? Is there a formula?
- Mon Feb 03, 2020 12:52 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Enthalpy
- Replies: 7
- Views: 410
Re: Enthalpy
How does enthalpy or change in enthalpy relate to q when pressure isn't constant?
- Mon Feb 03, 2020 12:50 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: work equations
- Replies: 5
- Views: 224
Re: work equations
What about when we are calculating the change in internal energy in a system under constant pressure? Work is involved, do we always use the negative sign in the expression for work? You don't necessarily need to worry about when to include the negative sign or not within -P delta V. If work is bei...
- Sun Feb 02, 2020 1:25 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Internal energy = State function
- Replies: 4
- Views: 275
Re: Internal energy = State function
It's just the way we calculate things and what we care about looking at based on the definition of the word. Internal energy only looks at the initial and final states and doesn't care about the path taken. Heat and work, on the other hand, we look at the path taken to get the value of both. If the ...
- Sun Feb 02, 2020 1:21 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Deriving Equation
- Replies: 3
- Views: 129
Re: Deriving Equation
delta H is plugged in to replace q and -PΔV is plugged in to replace w. q=ΔH because ΔH represents the heat gain or loss of a system quantitatively. w=-PΔV because: you start with force= P(external) x area -This is the formula for the pressure being exerted by the system also, the volume of the area...
- Sun Feb 02, 2020 1:12 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Work done BY vs work done ON
- Replies: 9
- Views: 306
Re: Work done BY vs work done ON
Work done on a system can indicate that pressure is being put on the system and decreasing its volume (compression)/heat is being transferred into the system through an endothermic reaction/ a variation of both. This will indicate that delta H is positive. When a system does work on the surroundings...
- Sun Feb 02, 2020 1:08 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: self test 4A.1A
- Replies: 2
- Views: 143
Re: self test 4A.1A
I followed your math and got the same answer. The only thing that I can guess is that maybe the book did prematurely round and keep their calculations to 4 sig figs or something. I think that your answers are close enough that you wouldn't be penalized if this were on a test.
- Sun Feb 02, 2020 12:56 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Phase change
- Replies: 20
- Views: 895
Re: Phase change
A positive delta H means energy is put in (endothermic) which is what is necessary to break the bonds that holds a solid together into a liquid. That's why change in enthalpy is positive.
- Wed Jan 29, 2020 10:20 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Define Reversible process
- Replies: 2
- Views: 253
Re: Define Reversible process
The whole point of a reversible process is that the tiniest change results in work being done. I think overall reversible is a confusing term. I just think of irreversible as doesn't change easily. If a system is reversible it means that all surrounding and system variables are basically the same (a...
- Wed Jan 29, 2020 10:11 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Systems at equilibrium
- Replies: 3
- Views: 195
Re: Systems at equilibrium
In chapter 4A of the book we learn about reversible processes. I think we're going to discuss it in class later on but what I gathered from lecture today and from the reading is that when the system is at equilibrium and stable, it is reversible. A reversible process is one where the tiniest change ...
- Wed Jan 29, 2020 10:05 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: State Property
- Replies: 6
- Views: 271
Re: State Property
State properties are properties where the value is determined by the current state, not the "path" taken to reach the state. For internal energy, to find the change you just subtract initial(U) from final(U) without thinking about the path taken in between (for example, if U jumped up and ...
- Wed Jan 29, 2020 10:02 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Isolated Systems
- Replies: 5
- Views: 282
Re: Isolated Systems
Especially if you want to know how a system changes over time (ex- thru a reaction) without being influences by any surroundings or outside factors, isolated systems are incredibly useful. Measuring equipment can be put inside of the system to properly gauge a change in some characteristic of the sy...
- Sat Jan 25, 2020 4:21 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpy
- Replies: 4
- Views: 189
Re: Bond Enthalpy
Bond Enthalpy is the enthalpy (essentially the energy) needed to break a bond. All bonds require an input of energy in order to be broken (see bond potential energy graph) and a positive enthalpy signifies that energy must be put in. This is why all bond enthalpies are positive. The bond enthalpy of...
- Fri Jan 24, 2020 4:50 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: pka
- Replies: 4
- Views: 292
Re: pka
A high pKa means a low Ka which means that a small amount of the acid molecules are deprotonated, making it a weak acid.
pKa=-log(Ka)
pKa=-log(Ka)
- Wed Jan 22, 2020 6:06 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding Heat and Constant Temperature
- Replies: 2
- Views: 122
Adding Heat and Constant Temperature
What does it mean that when you add heat to a system, its overall temperature remains constant? Isn't ice colder than boiling water (ie they have different temperatures)? Or does water as a solid have a uniform temperature, then liquid water has its own uniform temperature, then water vapor has its ...
- Mon Jan 20, 2020 1:06 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE
- Replies: 3
- Views: 118
Re: ICE
ICE is also generally used for weak acids and bases. With strong acids and bases, you can assume full protonation/deprotonation and assume that the concentration of the original strong acid or base becomes 0 and the concentration of the products is equal to the intitial acid/base concentration.
- Sat Jan 18, 2020 11:44 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: weak acid and strong base
- Replies: 2
- Views: 183
Re: weak acid and strong base
When you mix any acid and base, the result is water and a salt. Generally, I don't think we're going to be asked to find equilibrium constants or the pH of such reactions (at least not yet) but treat it as you would any other equation. Given the information provided, think about how much of the orig...
- Thu Jan 16, 2020 9:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 6B3
- Replies: 1
- Views: 159
6B3
6B3 asks you to find the pH of 0.025 M HCl first in a flask of volume 200.0 mL (part a) and then one of 250.0 mL (part b). I found the new molarity within each new volume and then found the pH of that but in the answers for part a, the book just found the pH of 0.025 M. I don't really get why; don't...
- Thu Jan 16, 2020 9:37 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: acidity and basicity constant
- Replies: 4
- Views: 208
acidity and basicity constant
When finding Ka or Kb, do you follow the same rules as we learned from last unit with Kp or Kc? Specifically, if one of the products of an acid reaction has a 2 coefficient, do you square the product concentration when finding Ka?
- Mon Jan 13, 2020 9:04 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kp and Kc
- Replies: 4
- Views: 222
Re: Kp and Kc
When it comes to gases, partial pressure (Kp) is more accurate for finding the equilibrium constant than Kc. For aqueous solutions obviously you can't use partial pressures so here you can use Kc. If concentrations are provided for gases rather than partial pressures, it's fine to use Kc and deal wi...
- Mon Jan 13, 2020 9:02 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Homework 5l. 29
- Replies: 2
- Views: 112
Re: Homework 5l. 29
2HCl(g)->H2(g) + Cl2(g) 0.22 bar 0 0 initial -2x +x +x change 0.22-2x +x +x final Partial P(H2) x Partial P (Cl2) K=------------------------------------ Partial P (HCl)^2 3.2x10^-34= x^2/(0.22-2x)^2 (square root both sides) 1.8x10^-17=x/0.22-2x (multiply both sides by denominator, distribute 1.8x10^...
- Mon Jan 13, 2020 8:41 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Autoprotolysis vs Autoionization
- Replies: 2
- Views: 225
Re: Autoprotolysis vs Autoionization
When it comes to water, I believe the two terms can be used interchangeably. Kw is referred to as either the autoprotolysis constant of water or the autoionization constant of water. They basically mean the same thing.
- Mon Jan 13, 2020 8:37 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: equilibrium constants and inputs
- Replies: 4
- Views: 173
equilibrium constants and inputs
When finding Kc, why do we ignore liquids and solids? What values do we assume the concentrations of liquids or solids to be once the reaction goes through? (ie- when we see a liquid in an equation, do we assume its molarity will be almost equal to 1 and that's why we ignore it? and why assume that ...
- Mon Jan 13, 2020 6:53 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Le Chatelier
- Replies: 3
- Views: 119
Re: Le Chatelier
The value of K itself will not be changed by anything except temperature. Other parameters such as pressure or concentration will cause the position of equilibrium to change but not the value of the equilibrium constant for that chemical equation for that temperature.
- Wed Jan 08, 2020 6:58 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Composite Equations
- Replies: 3
- Views: 1440
Re: Composite Equations
Can someone explain the process of combining two equations and determining how to combine their K's? How do you know which reactants will cancel each other out when you combine two equations? Also how do stoichiometric coefficients tie into this?