Search found 51 matches
- Thu Mar 12, 2020 4:31 pm
- Forum: Calculating Work of Expansion
- Topic: isobaric compression
- Replies: 7
- Views: 1690
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: 1025
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: 361
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: 688
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: 2673
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: 219
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: 486
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: 407
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: 509
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: 1184
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: 270
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: 358
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: 4422
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: 289
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: 1056
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: 86
- Views: 6838
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: 347
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: 20
- Views: 1327
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: 1321
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: 479
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: 463
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: 920
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: 546
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: 789
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: 39
- Views: 2047
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: 2902
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: 40
- Views: 2407
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: 192
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: 237
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: 886
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: 373
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: 128
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: 231
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: 533
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: 113
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: 324
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: 593
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: 2459
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: 910
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: 82
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: 114
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
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: 138
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: 332
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: 1141
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: 617
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: 573
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: 729
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: 546
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: 324
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: 216
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: 197
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?