## Search found 51 matches

Thu Mar 12, 2020 4:31 pm
Forum: Calculating Work of Expansion
Topic: isobaric compression
Replies: 7
Views: 151

### Re: isobaric compression

If you're compressing a gas and the process is isobaric, then most likely the temperature is decreasing since the equation PV=nRT holds that if volume is going down (compression) and pressure is staying the same (isobaric), then either n, R, or T is going to change. R is a constant so we can rule th...
Thu Mar 12, 2020 4:28 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Cv vs Cp
Replies: 17
Views: 303

### Re: Cv vs Cp

Generally it will be stated within the parameters of the problem whether or not pressure/volume is constant.
Thu Mar 12, 2020 4:27 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Determining the slow step
Replies: 4
Views: 74

### Re: Determining the slow step

So far in the examples we've been given in lecture, the slow step has been explicitly labelled
Thu Mar 12, 2020 4:25 pm
Forum: Phase Changes & Related Calculations
Topic: change in entropy
Replies: 7
Views: 251

### Re: change in entropy

If deltaS is less than 0, then that means that the overall change in entropy is negative--implying a decrease in spontaneity
Thu Mar 12, 2020 4:24 pm
Forum: Phase Changes & Related Calculations
Topic: delta G0 versus delta G
Replies: 15
Views: 451

### Re: delta G0 versus delta G

Delta G0 is the Gibbs free energy of a reaction at equilibrium whereas delta G is the gibbs free energy of a reaction at any given state
Thu Mar 12, 2020 4:20 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: rates
Replies: 2
Views: 31

### Re: rates

Sure! The rate of a reaction is the speed at which a reactant degrades and is usually expressed in some mol/s or mol/L*s whereas the rate constant, k, is a constant with no units that is generally multiplied to a concentration to find out its concentration at an equilibrium. Rate=Rate constant*[reac...
Sun Mar 08, 2020 5:37 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagrams
Replies: 7
Views: 76

### Re: Cell Diagrams

Either can be used if there is no solid metal on either the anode or cathode
Sun Mar 08, 2020 5:35 pm
Forum: Balancing Redox Reactions
Topic: Balancing a reaction
Replies: 5
Views: 87

### Re: Balancing a reaction

Basically what you want to do is split the reaction into two half reactions; add water and hydrogen/OH ions to either side to balance molecules and add electrons to either side to make the charges balance out. Then multiply either reaction by a coefficient to make sure that the # of electrons on eac...
Sun Mar 08, 2020 5:31 pm
Forum: Second Order Reactions
Topic: Half-life of Second-Order
Replies: 4
Views: 323

### Re: Half-life of Second-Order

To calculate it just substitute the value of the reactant concentration as it relates to t with 1/2[reactant]
Sun Mar 08, 2020 5:29 pm
Forum: Second Order Reactions
Topic: Non-integer orders
Replies: 7
Views: 398

### Re: Non-integer orders

Most likely not considering what we've covered in class
Sun Mar 08, 2020 5:28 pm
Forum: First Order Reactions
Topic: Determining order
Replies: 3
Views: 57

### Re: Determining order

If you're given the reaction itself then you can just see the constituent reactants and determine the rate order just based on that, but you can also tell what order a reaction is based on the graphs of concentration over time (i.e. linear graph of ln[reactant] vs t is 1st order, linear graph of rea...
Sun Mar 08, 2020 5:24 pm
Forum: General Rate Laws
Topic: affect of temperature on K
Replies: 4
Views: 63

### Re: affect of temperature on K

If the forward reaction is exothermic, then with an increase in temperature the reverse reaction is favored, meaning that k'>k
Sun Mar 01, 2020 9:41 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Why is delta U = 0 for isothermal reactions?
Replies: 11
Views: 254

### Re: Why is delta U = 0 for isothermal reactions?

Delta U is the change in internal energy of a system, which is dependent on its temperature. If T=0 then Delta U=0
Sun Mar 01, 2020 9:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Reaction Free Energy
Replies: 2
Views: 76

### Re: Reaction Free Energy

Depending on the pressure, the reaction can shift to favor either the products or reactants and the value of K also dictates whether or not a reaction is product favored (large K) or reactant favored (small K)
Sun Mar 01, 2020 9:00 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Work
Replies: 14
Views: 334

### Re: Work

If the system is doing work on the surroundings, like when the volume of something is expanding or heat is being released; but if something is being compressed or heat is being put in, then the surroundings are doing work on the system.
Sun Mar 01, 2020 8:57 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Kelvin or Celsius?
Replies: 47
Views: 1103

### Re: Kelvin or Celsius?

Technically it's all dependent on the value of R that you use, but in most cases you'll be given a value that incorporates Kelvin rather than Celsius
Sun Mar 01, 2020 8:54 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Why don't you have to convert pressure into concentration when doing lnQ?
Replies: 3
Views: 67

### Re: Why don't you have to convert pressure into concentration when doing lnQ?

I believe it was mentioned in our discussion section that the ratios are going to be the same (although I could be wrong on this)
Sat Feb 22, 2020 2:17 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: Spontaneous
Replies: 10
Views: 250

### Re: Spontaneous

If the Gibbs Free Energy is negative--that is, if T*DeltaS is larger than Delta H or Delta H is negative--then the reaction will be spontaneous. The inclusion of T as a variable shows that as temperature increases, all reactions eventually become spontaneous
Sat Feb 22, 2020 2:15 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: U vs H
Replies: 15
Views: 326

### Re: U vs H

The change in internal energy is a summation of the enthalpy and the work done on the system so Delta U is Delta H +w
Sat Feb 22, 2020 2:14 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Midterm 6D
Replies: 5
Views: 151

### Re: Midterm 6D

If I recall correctly there are two phase change options, one being the transition from solid to liquid and the other one being from liquid to gas. The entropy change associated with the latter option is larger
Sat Feb 22, 2020 2:12 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Reversible Systems
Replies: 4
Views: 209

### Re: Reversible Systems

In a reversible system what's happening is that heat is going into the system at basically the same rate that it's going out (think of it like if a balloon is slowly expanding vs just popping) and in an irreversible system you're going to get less work done and there will be a temperature change due...
Sat Feb 22, 2020 2:10 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: n in -nFE
Replies: 12
Views: 126

### Re: n in -nFE

In this particular case, since we're trying to talk about charge, n is the number of moles of electrons
Sat Feb 22, 2020 2:08 pm
Forum: Balancing Redox Reactions
Topic: Oxidizing/reducing agent
Replies: 7
Views: 106

### Re: Oxidizing/reducing agent

Basically the thing that is getting reduced is acting as an oxidizing agent since the other element/molecule is getting oxidized (and vice versa)
Sat Feb 22, 2020 2:06 pm
Forum: Balancing Redox Reactions
Topic: Charge of oxygen
Replies: 15
Views: 151

### Re: Charge of oxygen

The charge in this case will be 0 since Oxygen in this form is in a diatomic molecule.
Sun Feb 16, 2020 1:13 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: spontaneity
Replies: 34
Views: 690

### Re: spontaneity

If a reaction has an increase in entropy or a decrease in enthalpy, then it is more likely to be spontaneous. To compute the actual value you need to check if the Gibbs free energy of a reaction is negative and to do that you use the equation delta G=deltaH-T*deltaS
Sun Feb 16, 2020 1:11 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Joules or KJ?
Replies: 14
Views: 213

### Re: Joules or KJ?

Both work but I'd be careful to convert all your units to the same scale (either joules or kilojoules) because the equations we use for entropy give us the answer in joules whereas the equations we use to calculate enthalpy frequently use kilojoules
Sun Feb 16, 2020 1:09 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: R constants
Replies: 21
Views: 791

### Re: R constants

It primarily depends on the units used; as a general rule 0.08206 works when you're using ideal gas law and 8.314 works for calculating deltaS since it does the conversion from L atm to joules for you
Sun Feb 16, 2020 1:08 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: When to Use Certain Equations
Replies: 2
Views: 35

### Re: When to Use Certain Equations

The first equation is used when the reaction is not at equilibrium and there is some reaction quotient Q that is not equal to K whereas the second reaction assumes that the reaction has reached equilibrium and Q=K.
Sun Feb 16, 2020 1:06 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: DeltaS
Replies: 2
Views: 69

### Re: DeltaS

In isothermal expansion, there is no work being done since the volume is expanding in extremely small increments to the point where delta V starts to approach 0; if there is no work being done and we know that the change in the internal energy of the system is 0 since it is isothermal, then we can s...
Sun Feb 16, 2020 1:03 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free energy concept
Replies: 16
Views: 251

### Re: Gibbs Free energy concept

Gibbs Free Energy is basically a measure of the energy available to do work. In a more practical sense, if the delta G is negative, then there will be more energy available to do work instead of being contained within the chemical bonds of the product as potential energy; these types of reactions ar...
Sun Feb 16, 2020 12:59 pm
Forum: Van't Hoff Equation
Topic: Enthalpy, Entropy, and Gibbs Free Energy
Replies: 7
Views: 62

### Re: Enthalpy, Entropy, and Gibbs Free Energy

Although there isn't going to be a change in entropy/enthalpy, there is going to be a change in temperature that will alter the reaction constant K.
Tue Feb 11, 2020 3:15 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Spontaneity - Enthalpy
Replies: 1
Views: 52

### Re: Spontaneity - Enthalpy

Not necessarily; if the absolute value of the change in enthalpy is less than the absolute value of the change in entropy then delta G will be negative and the reaction will be spontaneous. Theoretically you could actually be decreasing entropy and still getting a spontaneous reaction as long as del...
Tue Feb 11, 2020 3:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: state property
Replies: 4
Views: 49

### Re: state property

The Gibbs free energy of a reaction is not dependent on the path the reaction takes but rather, the net change between the internal energy of the products vs the internal energy of a reactant, making it a state function
Tue Feb 11, 2020 3:01 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Internal energy of ideal gas
Replies: 6
Views: 163

### Re: Internal energy of ideal gas

There will always be some internal energy due to the movement of molecules in a system; however the change in internal energy will be 0
Tue Feb 11, 2020 3:00 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: delta H for isothermal reactions
Replies: 1
Views: 33

### Re: delta H for isothermal reactions

Enthalpy changes are dependent on changes in temperature, so if the change in temperature is 0, then then delta H=0
Tue Feb 11, 2020 2:58 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Thermodynamics
Replies: 6
Views: 87

### Re: Thermodynamics

When work is done on a system, the sign is positive; when work is done by a system, the sign is negative
Sun Feb 02, 2020 10:19 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Test 2 Question 7
Replies: 3
Views: 320

### Re: Test 2 Question 7

a cup of coffee is an open system in that the external temperature of the surroundings can affect the internal temperature of a system. A hot cup of coffee that exists in an area where the surrounding temperature is colder will allow for the heat transfer from the system to the surroundings.
Sun Feb 02, 2020 10:16 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Bomb Calorimeter
Replies: 5
Views: 1773

### Re: Bomb Calorimeter

A bomb calorimeter is a closed system, which means that there is no net change in volume. Since there is no change in volume there isn't any work being done and the change in internal energy (delta U) should be equal to q
Sun Feb 02, 2020 10:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Phase change
Replies: 20
Views: 176

### Re: Phase change

You're going from a state of lower energy to a state of higher energy when you go from a solid to a liquid (or a liquid to a gas) so the change in enthalpy should be positive
Sun Feb 02, 2020 10:08 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: States of a system
Replies: 3
Views: 37

### Re: States of a system

I believe it is the number of elements within a system raised to the power of possible system states (i.e. if you have 3 molecules which can occupy 4 chambers then you have 3^4 possible states)
Sun Feb 02, 2020 10:06 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Negative Enthalpy
Replies: 3
Views: 38

### Re: Negative Enthalpy

Spontaneous reactions depend on whether or not the delta G is negative; since the equation for delta G is
deltaH-T(deltaS), then if the enthalpy is positive you can still have a negative delta G (and a spontaneous reaction) if the absolute value of T(deltaS) is greater than the enthalpy change
Sun Feb 02, 2020 10:00 pm
Forum: Calculating Work of Expansion
Topic: Constant Pressure
Replies: 3
Views: 35

### Re: Constant Pressure

If they use the term "isobaric" in the problem it means that the pressure is staying constant
Sun Jan 26, 2020 8:27 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Energy of the reactants
Replies: 6
Views: 49

### Re: Energy of the reactants

It's an endergonic reaction since the reactants have less energy
Sun Jan 26, 2020 8:27 pm
Forum: Ideal Gases
Topic: R Constant
Replies: 18
Views: 260

### Re: R Constant

There are different values for R depending on the units that you are using in your calculations
Sun Jan 26, 2020 8:24 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Negative Square Root solving an ICE box
Replies: 13
Views: 106

### Re: Negative Square Root solving an ICE box

You probably shouldn't be getting a negative seeing as how the Acid/Base on the product side becomes a negative term when you set the entire equation equal to 0. Remember that it's b^2-4ac so the two negatives should cancel out
Sun Jan 26, 2020 8:21 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: La Chatelier's Principle
Replies: 8
Views: 206

### Re: La Chatelier's Principle

Increasing the concentration of the reactant will decrease Q, meaning that the reaction will shift towards the products in order to increase Q so that it can become = to K and vice versa
Sun Jan 26, 2020 8:19 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Weak acid/base
Replies: 14
Views: 160

### Re: Weak acid/base

Generally if you're given a Ka/Kb value in a problem it's most likely a weak acid/base but just as a general rule of thumb it has to do with the electronegativity difference
Sun Jan 26, 2020 8:18 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Changing K
Replies: 13
Views: 116

### Re: Changing K

Temperature changes K
Sun Jan 26, 2020 8:17 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Pressure vs. Volume
Replies: 6
Views: 81

### Re: Pressure vs. Volume

More V/Less P=shift to side with more mols and vice versa
Sun Jan 26, 2020 8:16 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: percent ionization
Replies: 5
Views: 53

### Re: percent ionization

If you have a small percentage of the initial then that means that the change is negligible so if you have something in the denominator like .01-(8*10^-9) that's pretty much the same thing as .01
Sun Jan 26, 2020 8:09 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Water Phase Change
Replies: 6
Views: 69

### Water Phase Change

Can someone reiterate how water as a gas has more energy as water as a liquid when they are booth at 100 degrees C?

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