## Search found 54 matches

Fri Mar 13, 2020 3:12 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Arrhenius Equation
Replies: 8
Views: 31

### 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: 22

### 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: 17

### 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: 52

### 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: 34

### 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: 58

### 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: 59

### 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: 485

### 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: 49

### 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: 35

### 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: 140

### 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).
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: 24

### 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: 68

### 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: 42

### 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: 22

### 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: 51

### 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: 60

### 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: 42

### 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: 37

### 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: 65

### 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: 52

### 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: 6
Views: 78

### 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: 81

### 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: 75

### 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: 54

### 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: 45

### 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: 51

### 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: 34

### 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: 35

### 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: 47

### 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: 39

### 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: 49

### 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: 27

### 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: 31

### 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: 65

### 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: 26

### 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: 113

### 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: 27

### 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: 40

### 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: 43

### 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: 32

### 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: 21

### 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: 33

### 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)
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: 30

### 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: 23

### 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: 66

### 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: 21

### 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: 22

### 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: 28

### 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: 23

### 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: 14

### 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: 39

### 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: 27

### 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: 38

### 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?