## Search found 51 matches

Sun Mar 18, 2018 5:21 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Reducing power
Replies: 2
Views: 4736

### Reducing power

I am confused on what it means for something to have a high reducing/oxidizing power. I read that if Ecell is more negative than it has greater reducing power but I am confused on why that is.
Sun Mar 18, 2018 12:53 am
Forum: Calculating Work of Expansion
Topic: Reversible vs. Irreversible
Replies: 2
Views: 293

### Reversible vs. Irreversible

Why do reversible reactions do more work than irreversible?
Sun Mar 18, 2018 12:41 am
Forum: Calculating Work of Expansion
Topic: Work done on or by system
Replies: 2
Views: 271

### Work done on or by system

If there is an increase in volume is the system inside always doing work (so therefore negative work) and if there is a decrease in volume the system inside is it always getting work done on it (so work is positive)?
Sat Mar 17, 2018 5:32 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity of liquid
Replies: 1
Views: 266

### Heat capacity of liquid

Why is it that the heat capacity of liquid is greater than solid or gas? I know that it means that it takes more heat to raise the temperature of liquid but i don't understand WHY that is the case.
Wed Mar 07, 2018 7:30 pm
Forum: General Rate Laws
Topic: Rate Laws
Replies: 3
Views: 225

### Re: Rate Laws

I think unless otherwise stated you assume only the concentration of the reactants factor into the rate law because that makes it easier to study the rate without interferences.
Wed Mar 07, 2018 7:27 pm
Forum: General Rate Laws
Topic: Reaction rates
Replies: 3
Views: 207

### Re: Reaction rates

Average rate is different based on which species you choose because it is dependent on the concentrations and that may change over time. Unique rate is the appearance or disappearance of a species divided by its stoichiometric coefficient so it will be the same for each reactant/product. Average rat...
Wed Mar 07, 2018 7:04 pm
Forum: First Order Reactions
Topic: Zero-order vs. First-order reaction graphs
Replies: 5
Views: 2297

### Re: Zero-order vs. First-order reaction graphs

Graphically, zero order reactions have a linear line when the concentration is plotted against time while in first order reactions have a linear line when ln[A] is plotted against time. So when given a graph you can identify what order it may be.
Wed Mar 07, 2018 7:00 pm
Forum: Zero Order Reactions
Topic: Slope From
Replies: 5
Views: 398

### Re: Slope From

The slope form is important in identifying the rate constant and also the order when given concentrations.
Wed Mar 07, 2018 1:52 am
Forum: General Rate Laws
Topic: Rate Law vs. Rate of reaction [ENDORSED]
Replies: 1
Views: 113

### Rate Law vs. Rate of reaction[ENDORSED]

I'm a bit confused on the difference between the rate of reaction, which is the change in the concentration of a species over change in time and rate law?
Rate law seems to be the same idea so i'm a bit confused.
Tue Mar 06, 2018 5:54 pm
Forum: General Rate Laws
Topic: Specification of Reactant/Product
Replies: 3
Views: 144

### Re: Specification of Reactant/Product

I believe that it would be incorrect because the average reaction rate differs based on the species but if it was a unique average rate than it would be correct even without the species because the rate would be the same regardless of the species.
Wed Feb 21, 2018 3:33 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: What is n when finding Standard Gibbs Rxn
Replies: 1
Views: 96

### What is n when finding Standard Gibbs Rxn

When finding the standard Gibbs Rxn we use the equation DeltaGn = -nFE. But just to clarify, it states that n is the electrons transferred so in a balanced redox reaction would that be the change in net mols? So when the redox reaction is balanced we add the coefficients and then see how many mols w...
Wed Feb 21, 2018 2:14 am
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Oxidization Question [ENDORSED]
Replies: 1
Views: 93

### Oxidization Question[ENDORSED]

In part A of 14.5 the half reaction is O3 (g) -> O2(g) and it states that this is being reduced. If the oxidation number is both 0 how can you know if it is being reduced or oxidized?
Tue Feb 20, 2018 11:09 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Standard Potential of a couple
Replies: 3
Views: 173

### Standard Potential of a couple

Can someone explain why the more negative the standard potential of a couple the greater its reducing strength and vice versa?
Tue Feb 20, 2018 8:49 pm
Forum: Balancing Redox Reactions
Topic: Acidic Solution vs. Basic Solution
Replies: 2
Views: 162

### Acidic Solution vs. Basic Solution

When balancing redox reactions will the question always say if its in an acidic vs basic solution or would we need to know the difference between the two?
Wed Feb 14, 2018 2:38 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.15 Question
Replies: 2
Views: 207

### 9.15 Question

For question 9.15 the change in entropy for freezing of H20 at 0.00C uses a negative deltaH of fusion in the solution manual but this value is not negative in the chart 8.3. Just to clarify, is it negative here because the reaction is going from liquid to ice so the change in entropy is negative?
Wed Feb 14, 2018 12:26 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: The overall change in Entropy [ENDORSED]
Replies: 1
Views: 173

### The overall change in Entropy[ENDORSED]

In section 9.10 in the textbook it states that since deltaU = q+w it follows that q rev must be greater than q irrev because only than can the sums of q and w be the same for the two paths. Can someone explain what that means?
Mon Feb 12, 2018 12:15 am
Forum: Balancing Redox Reactions
Topic: redox reactions and salts
Replies: 2
Views: 326

### Re: redox reactions and salts

Not all redox reactions have salt products. Overall a redox reaction is any reaction where there is a transfer of electrons from one thing to another. It only seems that all redox reactions have salt products because redox reactions are common in electrochemical reactions.
Mon Feb 12, 2018 12:10 am
Forum: Balancing Redox Reactions
Topic: Oxidation vs. reduction
Replies: 8
Views: 322

### Re: Oxidation vs. reduction

When something loses electrons it is oxidized and when it gains electrons it is reduced. A tip to remember as well though is that an oxidizing agent is the one being reduced and the reducing agent is the one being oxidized and both are on the reactant side of the redox equation.
Mon Feb 12, 2018 12:06 am
Forum: Balancing Redox Reactions
Topic: Nature
Replies: 5
Views: 281

### Re: Nature

I think that they occur together because when there is a oxidation there is a reduction and vice versa.
Tue Feb 06, 2018 1:52 am
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Open, closed, or isolated test 1 question
Replies: 10
Views: 795

### Re: Open, closed, or isolated test 1 question

It is an open system because in a vial both matter and energy can be exchanged with the surroundings making it an open system
Tue Feb 06, 2018 1:48 am
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Delta U (Concept Clarification)
Replies: 6
Views: 291

### Re: Delta U (Concept Clarification)

I think I read in the book that delta U is 0 because the molar internal energy of an ideal gas is U=3/2 RT and since internal energy and temperature are state dunctions DeltaU = 3/2 R DeltaT. So in an isothermal expansion where delta t = 0 , DeltaU would equal 0 as well.
Tue Feb 06, 2018 1:43 am
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy
Replies: 7
Views: 343

### Re: Gibbs Free Energy

The way i think of it is that changing the state of a system requires energy (delta H) but when molecules exchange heat with its surroundings some molecules spontaneously arrange themselves so that the energy needed to change the state is less than the total energy required. The energy you actually ...
Sun Jan 28, 2018 11:42 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: 9.3
Replies: 5
Views: 329

### Re: 9.3

In the beginning the energy is negative because heat is leaving the system (making it negative) but when heat is added it to the system then it is positive
Wed Jan 24, 2018 2:23 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Homework 8.55
Replies: 2
Views: 114

### Homework 8.55

The given reaction enthalpies are 2Ba (s) + O2 (g) ---> 2BaO (s) deltaH= -1107 kj 3Al (2) + O2 (g) ---> Al2O3 (s) deltaH = -1676 kj and we have to calculate the reaction enthalpy for 3 BaO + 2Al ---> Al2O3 + 3Ba In the solution manual the first reaction is reversed and multiplied by 3/2 so it become...
Tue Jan 23, 2018 11:58 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: The relation between deltaH and deltaU (enthalpy and internal energy)
Replies: 1
Views: 154

### The relation between deltaH and deltaU (enthalpy and internal energy)

In the textbook it said that reaction enthalpy (deltaH) is more positive (less neg) than the reaction internal energy for reactions that generate gas. The book gives an explanation but I have trouble understanding it!
Sun Jan 21, 2018 4:29 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Heat v Thermal Energy
Replies: 3
Views: 163

### Re: Heat v Thermal Energy

Heat is the transfer of thermal energy from an object of higher energy to an object of lower energy while thermal energy is the total energy associated to a system at a given temperature.
Sun Jan 21, 2018 4:04 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat vs. Thermal Energy
Replies: 3
Views: 177

### Re: Heat vs. Thermal Energy

The way I think of it is that Heat is the TRANSFER of thermal energy from one object of higher energy to another of a lower energy while Thermal Energy is the sum of all the kinetic energy of the object.
Sun Jan 21, 2018 2:58 pm
Forum: Calculating Work of Expansion
Topic: work done on and by the system
Replies: 12
Views: 714

### Re: work done on and by the system

I'm fairly certain that work is positive (energy gained) when work is done BY the system and work is negative (energy lost) when work is done ON the system
Sat Jan 13, 2018 8:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Standard Enthalpy of Formation (pure substance)
Replies: 3
Views: 769

### Standard Enthalpy of Formation (pure substance)

I was just wondering why the standard enthalpy of formation of an element in its most stable form is zero? I know that this was "by definition" but I was just wondering why specifically it was 0.
Sat Jan 13, 2018 8:48 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Heat and Ethalpy
Replies: 3
Views: 180

### Re: Heat and Ethalpy

I think that heat is the energy transferred in thermal reactions while enthalpy is the total energy in a thermodynamic system.
Sat Jan 13, 2018 8:31 pm
Forum: Phase Changes & Related Calculations
Topic: Constant temp
Replies: 3
Views: 206

### Re: Constant temp

Essentially the temperature does not change because the energy is used to actually change the phases and not to heat the substance. So for example if ice is going to liquid the energy is used to melt the ice not warm the mixture so the temp remains constant.
Sat Dec 09, 2017 2:11 am
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: Ka and pKa
Replies: 1
Views: 255

### Re: Ka and pKa

The difference between Ka and PKa is that Ka shows the proton donating strength of the acid and it is mathematically [H3O+][A-]/[HA] while Pka is the -log Ka. The smaller the value of Ka, the larger the value of pKa, the weaker the acid.
Sat Dec 09, 2017 2:04 am
Forum: Bronsted Acids & Bases
Topic: Bronsted acids in products
Replies: 2
Views: 236

### Re: Bronsted acids in products

I'm pretty sure you can have Bronsted acids and bases on the product side as well as conjugate acid-base pairs and since the reactions are reversible it would make sense for it to be on both sides of the equilibrium.
Fri Dec 01, 2017 6:59 pm
Forum: Lewis Acids & Bases
Topic: Strong acid+weak base
Replies: 2
Views: 248

### Re: Strong acid+weak base

The conjugate for a strong acid is a weak base and a conjugate for a strong base is a weak acid. I am pretty sure that this applies to Bronsted acids/bases.
Fri Dec 01, 2017 6:46 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Le Chatelier's Principle
Replies: 2
Views: 261

### Re: Le Chatelier's Principle

Le Chatelier's principle states that if something disturbs the equilibrium, the positions of equilibrium will shift to counteract the change and re-establish the equilibrium So for example if in A + B <-> C +D if the concentration of A is increased than the equilibrium positions will shift and more ...
Mon Nov 20, 2017 12:51 pm
Forum: *Molecular Orbital Theory (Bond Order, Diamagnetism, Paramagnetism)
Topic: Difference Between Sigma and Pi Bonds [ENDORSED]
Replies: 4
Views: 944

### Re: Difference Between Sigma and Pi Bonds[ENDORSED]

sigma bonds are end to end interactions that allow the atom to rotate around the internuclear axis while pi bonds are overlapping side by side bonding that does not allow atoms to rotate. There can only be one sigma bond between two atoms while there can be additional pi bonds.
Mon Nov 20, 2017 12:43 pm
Forum: Hybridization
Topic: bent molecular structure [ENDORSED]
Replies: 4
Views: 374

### Re: bent molecular structure[ENDORSED]

A molecule with two bonded electrons and two lone pair electrons will be bent because the lone pairs on the central atom repel each other and cause the bonded electrons to move farther apart which changes the structure from linear to bent
Mon Nov 20, 2017 12:39 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Polar ve non polar [ENDORSED]
Replies: 7
Views: 520

### Re: Polar ve non polar[ENDORSED]

When determining if a compound is polar or nonpolar I would look at the overall charge of the compound so that the dipole moments cancel each other out. Visually you can determine a non polar or polar compound by looking at the symmetry of the lewis structure and if it is symmetrical it is non polar...
Mon Nov 20, 2017 12:35 pm
Forum: Naming
Topic: Ch. 17 Problem 29a [ENDORSED]
Replies: 4
Views: 282

### Re: Ch. 17 Problem 29a[ENDORSED]

the suffix -ate indicates that the compound has a negative charge and ferr is from iron so ferrate shows that the iron compound is negative
Sun Nov 12, 2017 11:14 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone pairs versus bonding pairs
Replies: 3
Views: 444

### Re: Lone pairs versus bonding pairs

I believe it is due to the shape of lone pairs vs. bonding pairs. Bonding pairs are electrons that are between two atoms so the electrons are farther from the atom but more localized. Lone pair electrons however are pulled closer to the nucleus of the atom since the opposing negative charge from the...
Sun Nov 12, 2017 10:49 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Central Atom
Replies: 4
Views: 337

### Re: Central Atom

The rule is generally that the most electronegative atom is the central atom since these atoms are more open to sharing electrons but in this case since sulfur is explicitly stated in the problem you would use sulfur.
Mon Oct 30, 2017 12:37 pm
Forum: Lewis Structures
Topic: Central Atom [ENDORSED]
Replies: 3
Views: 209

### Re: Central Atom[ENDORSED]

Usually the least electronegative atom goes in the center. This is because most times if an atom has low electronegativity than it is more likely to share electrons and form bonds.
Mon Oct 30, 2017 12:31 pm
Forum: Formal Charge and Oxidation Numbers
Topic: when to calculate formal charge [ENDORSED]
Replies: 3
Views: 315

### Re: when to calculate formal charge[ENDORSED]

When there are resonance structure you should find the formal charge to determine which structure is the most stable and therefore the ideal structure. You find the formal charge in order to compare them and find the most stable one. I hope that makes some sense
Mon Oct 30, 2017 12:28 pm
Forum: Trends in The Periodic Table
Topic: Electron affinity [ENDORSED]
Replies: 4
Views: 308

### Re: Electron affinity[ENDORSED]

Electron Affinity is different from electronegativity in that Electro Affinity is the amount of energy released when a neutral atom attracts an electron to form a negative ion while electronegativity is the atoms ability to attract electrons to it. I hope that makes sense. They are similar in that t...
Mon Oct 30, 2017 12:18 pm
Forum: Lewis Structures
Topic: Lewis Dot Diagrams [ENDORSED]
Replies: 2
Views: 159

### Re: Lewis Dot Diagrams[ENDORSED]

No but its better if you start on the side not facing another element so that after you have all the valence electrons drawn out you can decide how these two elements bond.
Fri Oct 20, 2017 6:05 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Aufbau Principle - Carbon
Replies: 2
Views: 747

### Re: Aufbau Principle - Carbon

You use the number of electrons and start from the lowest subshell to the highest! So first in the example, carbon has 6 electrons so for the first subshell s, it holds two electrons so its 1s2 and then the next is 2s which also holds 2 electrons so its 2s2 and so with the remaining two electrons yo...
Fri Oct 20, 2017 5:48 pm
Forum: Wave Functions and s-, p-, d-, f- Orbitals
Topic: Orbitals, Subshells, and Shells
Replies: 4
Views: 215

### Re: Orbitals, Subshells, and Shells

Shells are the electrons around the nucleus and within the shells are the subshells (s,p,d,f) and within the subshells are orbitals. Also i think the subscripts are for the position of different orbitals in the p subshell!
Thu Oct 12, 2017 11:49 am
Forum: Photoelectric Effect
Topic: Energy in kj or j when solving a problem?
Replies: 10
Views: 815

### Re: Energy in kj or j when solving a problem?

I would use J since it makes the calculations simpler (since if you used kj you would need to change all of the j to kj so that all the units remain uniform) and if the answer asks for kj you can convert it as the last step of the problem.
Thu Oct 12, 2017 11:44 am
Forum: Properties of Light
Topic: Prefix Conversion
Replies: 12
Views: 731

### Re: Prefix Conversion

It depends on the problem! When you are calculating, the numbers should have the same prefix so in that case you would do the prefix conversion before the problem. (ex: if you are using the equation M=moles/L and you have to find the missing moles given M and mL of a solution you would need to do pr...
Thu Oct 05, 2017 6:27 pm
Forum: Balancing Chemical Reactions
Topic: Combustion [ENDORSED]
Replies: 6
Views: 587

### Re: Combustion[ENDORSED]

I'm pretty sure that both Carbon and Hydrogen are required since both H20 and Co2 need to be products for the equation to be a combustion. So the equation you sent is a combustion since it fulfills both requirements! I hope that answered your question!
Thu Oct 05, 2017 6:19 pm
Forum: Empirical & Molecular Formulas
Topic: Empirical Coefficients [ENDORSED]
Replies: 12
Views: 1456

### Re: Empirical Coefficients[ENDORSED]

As far as I know, if the number is within .1 from a whole number than you would just round to that whole number. However if its more than that you would need to multiply it by a number to get it to a whole number. So if it is .25 than you would multiply by 4 or if its .5 you would multiply by 2 and ...

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