Search found 101 matches
- Mon Mar 09, 2020 9:45 pm
- Forum: General Rate Laws
- Topic: 7A.3
- Replies: 1
- Views: 156
Re: 7A.3
Oxygen here is the reactant and therefore its final-initial will be a negative value and the negative sign you see in the unique rate formula takes care of that negative sign and change the rate into a positive one. For the reason of comparing, all rates are considered to be positive in this type of...
- Mon Mar 09, 2020 9:42 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: midterm q3d
- Replies: 1
- Views: 208
Re: midterm q3d
Since the pka is lower than the ph given, the acetic acid will act as an acid and will partially dissociate into H3o+ and CH3COO^-. Therefore, its net charge is -1.
- Mon Mar 09, 2020 9:39 pm
- Forum: General Rate Laws
- Topic: 7A 15
- Replies: 4
- Views: 293
Re: 7A 15
It's independent if changing its concentration does not affect the rate of the reaction.
- Mon Mar 09, 2020 9:37 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Question on Midterm
- Replies: 4
- Views: 372
Re: Question on Midterm
For this question, since specific heat is an extensive property, a smaller volume of water will have a lower specific heat and have a larger increase in temperature. This option is also the most concentrated.
- Sun Mar 01, 2020 9:11 pm
- Forum: General Science Questions
- Topic: Thermodynamics and Limiting Reactants
- Replies: 1
- Views: 188
Re: Thermodynamics and Limiting Reactants
If the problem does not specify whether the reaction happens in the excess of reactants, you should always consider the possibility of limiting reactants.
- Sun Mar 01, 2020 9:00 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5.61
- Replies: 2
- Views: 299
Re: 5.61
It will be included in the equilibrium expression. The only things not included will be elements in the state of solid or liquid.
- Sun Mar 01, 2020 8:58 pm
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: 6N.3
- Replies: 6
- Views: 451
Re: 6N.3
You should use appendix 2 to find the half-reactions happening in cathode and anode. Remember, cathode is the one with a higher E. Then balance the half-reactions and write them out to determine Q. Faraday's constant was not used because it was included in the formula given in the book after multipl...
- Sun Mar 01, 2020 8:54 pm
- Forum: Kinetics vs. Thermodynamics Controlling a Reaction
- Topic: thermo or kinetics?
- Replies: 9
- Views: 695
Re: thermo or kinetics?
Look at whether it's spontaneous(thermodynamics) and whether the reaction occurs at a fast rate(kinetics).
- Sun Mar 01, 2020 8:52 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: 5J 15.
- Replies: 1
- Views: 191
Re: 5J 15.
You might have used the wrong units. The G given in the appendix is in kJ but if you are using 8.314 as your R, convert kJ to J. Your standard G is wrong. You should check your calculations and see if you still have that number. I got 91.12 kJ/mol and this will give the answer in the solutions manua...
- Sun Feb 23, 2020 8:42 pm
- Forum: Balancing Redox Reactions
- Topic: Adding H2O and OH- to Balance
- Replies: 5
- Views: 293
Re: Adding H2O and OH- to Balance
In balancing half reactions, the first step is always to balance the number of oxygen atoms by adding H2O. The next step is to balance the H atoms, and this is what's different. In an acidic solution, after you balance the O atoms, you will balance the H atoms by adding H+ on the side that needs it,...
- Sun Feb 23, 2020 8:33 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6L.1 A
- Replies: 2
- Views: 222
Re: 6L.1 A
Write out the half reactions and balance them will help you find the number of electrons transferred in the process and hence n in the formula.
- Sun Feb 23, 2020 8:28 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: 6L. 3
- Replies: 4
- Views: 292
Re: 6L. 3
The anode is always on the left and the cathode is always on the right. You can also verify this by writing out the half reactions and see where oxidation and reduction happen.
- Sun Feb 23, 2020 8:27 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cathode vs Anode
- Replies: 11
- Views: 863
Re: Cathode vs Anode
Cathode is where reduction happens and anode is where oxidation happens.
- Tue Feb 18, 2020 9:19 pm
- Forum: Balancing Redox Reactions
- Topic: Whats the difference between oxidizing agent and oxiadation
- Replies: 6
- Views: 304
Re: Whats the difference between oxidizing agent and oxiadation
Oxidizing agent is the element that does the oxidation(taking away electrons from another element, and therefore the oxidizing agent is reduced). Oxidation is when electrons are lost, which represents the element that the oxidizing agent is acting upon.
- Tue Feb 18, 2020 9:16 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Standard Gibbs Free Energy Conditions
- Replies: 4
- Views: 337
Re: Standard Gibbs Free Energy Conditions
Temperature is not a condition of standard state but 298 K is usually used when standard state values are given. Temperature can be any value in a standard state condition. If the question is in STP(standard temperature and pressure), the temperature is 273k, but this is different from standard state.
- Tue Feb 18, 2020 9:09 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Adding Inert Gas
- Replies: 20
- Views: 1016
Re: Adding Inert Gas
Adding an inert gas will not have effect on the system because the inert gas does not participate in the actual chemical reaction and does not change the partial pressure or the volume(therefore concentration) of the reactants and products.
- Tue Feb 18, 2020 9:07 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: converting T to kelvin
- Replies: 46
- Views: 3188
Re: converting T to kelvin
If it's merely change in temperature, yes, because the conversion to K by adding 273.15 will cancel out. However, if you are using it like 1/T2-1/T1, then you will have to convert it.
- Tue Feb 18, 2020 9:06 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: reaction at equilibrium
- Replies: 6
- Views: 428
Re: reaction at equilibrium
Delta G is zero when an equation is at equilibrium because it has no tendency to shift to the reactant or product side but rather just stay as it is.
- Thu Feb 13, 2020 11:17 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Mean bond enthalpies
- Replies: 3
- Views: 256
Re: Mean bond enthalpies
This is so because bond enthalpy measures the change in energy when breaking bonds. On the reactant side, bonds are broken but on the product side bonds are formed; therefore, we use reactants-products to give the bond enthalpy on the product side a negative sign, which makes sense because forming b...
- Thu Feb 13, 2020 11:14 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: Why is delta U = 0 for isothermal reactions?
- Replies: 11
- Views: 4114
Re: Why is delta U = 0 for isothermal reactions?
In an isothermal process, the average kinetic energy of the molecules stay the same and since there is no force between the molecules, the potential energy also stays the same. Therefore, delta U=0.
- Thu Feb 13, 2020 11:13 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: 4C.3
- Replies: 2
- Views: 301
Re: 4C.3
at constant pressure, delta H=q=765 J. The molar heat capacity of a monatomic ideal gas at constant pressure is 5/2 R, which is 20.785J/kmol. To calculate temperature change, use q/(C*the number of mols of Kr), which is equal to 44.89K. The final temp at constant pressure is therefore 343K. At const...
- Thu Feb 13, 2020 10:59 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: 4F.17
- Replies: 1
- Views: 164
Re: 4F.17
Since entropy is a state function, to calculate the entropy of vaporization of water, you can use the equation: entropy change of heating the water from 85 to 100+entropy change of vaporizing the water at 100(constant temp.)+entropy change of cooling the vapor from 100 to 85. 75.3*ln[(100+273)/(85+2...
- Thu Feb 13, 2020 10:53 pm
- Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
- Topic: 4H.9
- Replies: 3
- Views: 313
Re: 4H.9
1 mol of atoms bound into diatomic molecules means there are 0.5 mol of diatomic molecules(1 mol*(1 mol molecule/2 mol atoms). This means the entropy of this will be lower than that of 1 mol of atoms because there are more single atoms and hence greater disorderliness.
- Tue Feb 04, 2020 10:42 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: Extensive Property
- Replies: 4
- Views: 267
Re: Extensive Property
Extensive property depends on the amount of the substance. Heat capacity is an extensive property because if you have 1000L water, it will have a high heat capacity(rise slower in temperature) than 1L of water. Specific heat capacity is not an extensive property because the unit is typically in J*De...
- Tue Feb 04, 2020 10:37 am
- Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
- Topic: isothermal reversible expansion
- Replies: 2
- Views: 100
Re: isothermal reversible expansion
Yes, buy you are missing a T in your equation. The equation should be -nRTln(V2/V1)=Work of system.
- Tue Feb 04, 2020 10:36 am
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Total internal energy calculation(Utotal)
- Replies: 1
- Views: 171
Re: Total internal energy calculation(Utotal)
The change of internal energy of a system is zero in isothermal expansion. This formula is related to the equipartition theory and can be used to calculate the internal energy of molecules or atoms by taking into account rotational and translational energy.
- Tue Feb 04, 2020 10:28 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: Degeneracy
- Replies: 1
- Views: 66
Re: Degeneracy
Degeneracy is a measure of the number of ways molecules or compounds can be arranged in the same total energy. This is is related to the idea of entropy because it takes into account the number of microstates possible, which all contribute to the disorderliness or randomness of a system(spontaneity)...
- Tue Feb 04, 2020 10:19 am
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Equation for q
- Replies: 4
- Views: 129
Re: Equation for q
The first one is used when the specific heat is given in terms of J/K/mol(molar specific heat).
- Mon Jan 27, 2020 9:46 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Reversible and Irreversible Expansion
- Replies: 2
- Views: 65
Re: Reversible and Irreversible Expansion
Reversible expansion means when the expansion can be reversed by an infinitesimal change, while irreversible means when an infinitesimal change will not reverse the direction of expansion.
- Mon Jan 27, 2020 9:43 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: 4B.5 and 4B.13 part a
- Replies: 2
- Views: 147
Re: 4B.5 and 4B.13 part a
You would use 1L*atm=101.325J. This can be found in a example problem on page 247.
- Mon Jan 27, 2020 9:41 pm
- Forum: Concepts & Calculations Using First Law of Thermodynamics
- Topic: Work done BY vs work done ON
- Replies: 9
- Views: 242
Re: Work done BY vs work done ON
Work done by a system is when a system does work on the surrounding, such as gas pushing out the piston and expand its volume. This will result in a negative W value because the system LOSES ability to do work now that it can no longer push on the piston because the pressure under the piston and the...
- Mon Jan 27, 2020 9:34 pm
- Forum: Phase Changes & Related Calculations
- Topic: Enthalpy of sublimation?
- Replies: 8
- Views: 1333
Re: Enthalpy of sublimation?
Since enthalpy is a state function and sublimation means the subject goes from a solid to a gas, the enthalpy of sublimation=heat involved in fusion+heat involved in vaporization
- Mon Jan 27, 2020 9:31 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Calorimeter
- Replies: 3
- Views: 95
Re: Calorimeter
The calorimeter often consists of the container and a solvent(typically water). The system refers to the chemical reaction happening right inside the solution, and the surroundings would be the solvent(the water) and the container.
- Mon Jan 27, 2020 9:28 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Chemical Equilibria
- Replies: 4
- Views: 248
Re: Chemical Equilibria
When a reaction has reached equilibrium, it means that the forward and reverse rate of the chemical reaction is the same and therefore there is no change in the concentration of products and reactants even though the system is still active.
- Mon Jan 20, 2020 9:48 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: pH and pOH in Reactions
- Replies: 3
- Views: 175
Re: pH and pOH in Reactions
Since the solvent here is water, there will be H3O+ due to the autoprotolysis of water.
- Mon Jan 20, 2020 9:43 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: pH sig figs
- Replies: 9
- Views: 387
Re: pH sig figs
In pH value, only the numbers after the decimal point count as sig.figs., so you need to write as many numbers after the decimal point as there are in the number of sig.figs. in the question.
- Mon Jan 20, 2020 9:38 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pressure goes to less moles of gas explaination
- Replies: 4
- Views: 186
Re: Pressure goes to less moles of gas explaination
Pressure only affect the equilibrium concentration if there is a change in volume since a change in volume will affect the concentration of the molecules involved in the chemical reaction because of the formula Concentration=n/V. Increasing pressure by adding inert gas will not affect the volume and...
- Mon Jan 20, 2020 9:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: parts of salts that don't affect pH
- Replies: 4
- Views: 127
Re: parts of salts that don't affect pH
All the conjugate base/acid of a strong acid or base will not affect the pH of the solution because they are the extremely weak conjugate base and acid of strong acid and base and therefore will not play a role in changing the pH level.
- Mon Jan 20, 2020 9:31 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Equilibrium constants vs equilibrium of the P&R
- Replies: 3
- Views: 102
Re: Equilibrium constants vs equilibrium of the P&R
This is asking how will a reaction shift if we start with more reactants. You can think of it as the reaction quotient Q. If we start with more reactants, Q will be smaller than k and therefore the reaction will shift to the right to produce more products.
- Tue Jan 14, 2020 10:40 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5J.9b
- Replies: 8
- Views: 286
Re: 5J.9b
Yes. The system will try to minimize the decrease in reactants by making the reaction to shift to the left and create more reactants when some are lost.
- Tue Jan 14, 2020 10:38 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: 5.33
- Replies: 6
- Views: 306
Re: 5.33
The chemical reaction is an endothermic reaction because it's breaking the bond of one molecule to separate it into two molecules. Therefore, increasing the temperature will lead the reaction to shift to the product side.
- Tue Jan 14, 2020 10:24 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Kp vs Kc
- Replies: 4
- Views: 103
Re: Kp vs Kc
If you are given enough information to calculate the molar concentration of all of the species in the reaction, you can use Kc even if the species are all in gaseous state. Sometimes the question only gives partial pressures, which means you can only use Kp in that case.
- Tue Jan 14, 2020 10:08 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Autoprotolysis
- Replies: 8
- Views: 187
Re: Autoprotolysis
Water is amphiprotic and can thus act as both a proton donor and a proton acceptor. Therefore, when there are two water molecules, one of them loses a proton(H+) and the other accepts it, resulting in a H3O+ and a OH- molecule.
- Tue Jan 14, 2020 10:06 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5I.19
- Replies: 2
- Views: 85
Re: 5I.19
First, calculate the molar concentration of H2 and I2 in the flask, which is n/v. From there, since the question says that 60% of the hydrogen gas reacted at equilibrium, it means that to reach equilibrium, H2 reduced by 0.6 of its original concentration. Therefore you will multiply 0.6 by the molar...
- Wed Jan 08, 2020 7:34 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: changing K
- Replies: 4
- Views: 164
Re: changing K
Yes. The formula for calculating both equilibrium constant is the same and the underlying concept is also the same: the equilibrium constant is the same under the same temperature despite changes made to partial pressures or concentrations.
- Wed Jan 08, 2020 7:31 pm
- Forum: Ideal Gases
- Topic: Solids and Liquids
- Replies: 7
- Views: 391
Re: Solids and Liquids
They are not included because they are not dissolved and hence their concentration is constant or cannot be calculated. Even if you put some more pure solid or some more pure liquid into the solution, you are just increasing the amount of such solid or liquid but their concentration does not change.
- Wed Jan 08, 2020 7:19 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Reverse reaction
- Replies: 6
- Views: 217
Re: Reverse reaction
The reverse reaction will begin when Q is larger than K, because in order for Q to approach K, it needs to get smaller, and the only way to do that is to make the denominator of the Q expression, or the concentration of reactants, higher.
- Wed Jan 08, 2020 7:14 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Reaction Direction
- Replies: 5
- Views: 229
Re: Reaction Direction
You can determine the direction that a reaction goes to by looking at the Q and K value. If the Q value is smaller than the K value, then in order for the reaction to reach K, or equilibrium, there needs to be more products, and if the Q is larger than the K value, there needs to be more reactants f...
- Wed Jan 08, 2020 7:10 pm
- Forum: Ideal Gases
- Topic: K and Q
- Replies: 13
- Views: 278
Re: K and Q
You use Q when the reaction is not in equilibrium and you use K when the reaction is in equilibrium.
- Fri Dec 06, 2019 9:02 am
- Forum: Bronsted Acids & Bases
- Topic: 6A.9 a
- Replies: 3
- Views: 273
Re: 6A.9 a
This is because NH4I will dissociate in water and the definition of a bronsted acid is a proton donor and NH4+, being a strong conjugate acid of a weak base NH3, will donate its proton to the water molecule. On the other hand, I- is the weak conjugate base of a strong acid HI and will not affect the...
- Sun Dec 01, 2019 5:36 pm
- Forum: Bronsted Acids & Bases
- Topic: How to tell
- Replies: 4
- Views: 261
Re: How to tell
The definition of bronstead acid/base is that it is a proton donor/acceptor. Looking at NH3, the hydrogen atoms bound to the nitrogen are not likely to fall off and bind to another atom since NH bonds are not polar enough to give the hydrogen a sufficiently positive charge to allow it to bind to an ...
- Sun Dec 01, 2019 5:32 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: Chelate and polydentate
- Replies: 2
- Views: 133
Re: Chelate and polydentate
A chelating ligand is a special type of ligand that binds to the central transitional metal at more than one site, forming a ring-like structure. Chelates are especially important in biological systems(Cisplatin can prevent DNA replication; myoglobin carries oxygen...). This relates to a ligand bein...
- Sun Dec 01, 2019 5:28 pm
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: 6B.3
- Replies: 2
- Views: 78
Re: 6B.3
We must input the concentration(mol*L^-1) when using the -log formula to calculate pH level, therefore, you will need to divide the result you got from your first calculation by 0.250L and then input the result into -log to calculate the pH level.
- Sun Dec 01, 2019 5:24 pm
- Forum: Bronsted Acids & Bases
- Topic: 6A.9 a
- Replies: 3
- Views: 273
Re: 6A.9 a
The chemical equation is not balanced(The I2 should be just I^-(aq)). After correcting this, writing the net ionic equation, the I^- ions will cancel out and the species left are NH4+,H2O,H3O^+,NH3. Since the proton donator is NH4+, NH4+ is the bronsted acid.
- Sun Dec 01, 2019 5:18 pm
- Forum: Shape, Structure, Coordination Number, Ligands
- Topic: structure of water
- Replies: 4
- Views: 209
Re: structure of water
Although there are two lone pairs of atoms on the oxygen atom, it can use only one of those pairs to bind to a transitional metal and the other pair would then not be in the correct geometry to bind to the transition metal on a different site.
- Sun Nov 24, 2019 8:21 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Polarity
- Replies: 4
- Views: 174
Re: Polarity
Just like how vectors can only cancel out each other when they are opposite to each other, you can draw out the dipole moment in a molecule and see if they cancel, but you must solve this by using the VSEPR model instead of the lewis structure since the VSEPR gives a more accurate 3D shape. A specia...
- Sun Nov 24, 2019 8:17 pm
- Forum: Ionic & Covalent Bonds
- Topic: Hydrogen Bond Sites
- Replies: 5
- Views: 370
Re: Hydrogen Bond Sites
Hydrogen bonding happens when and H attached to N,O, or F is bonded to the N,O,F on the other molecule. Therefore, whenever a N, O, or F atom has a lone pair of electrons, it can be bonding site.
- Sun Nov 24, 2019 8:11 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Hw Problem (boiling point)
- Replies: 1
- Views: 118
Re: Hw Problem (boiling point)
Ionic bond is the strongest bond and therefore KCl and KI will have higher boiling points than H2S and H2O. Between KCl and KI, because the iodine atom is larger than Cl and is more polarizable, the bonds between KCl formula units have some covalent character and is therefore weaker than KCl. Betwee...
- Sun Nov 24, 2019 8:05 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Lone Pairs on Cenrtral Atom
- Replies: 11
- Views: 573
Re: Lone Pairs on Cenrtral Atom
The repulsive force between electrons is ranked as, lone-pair-lone-pair>lone-pair-electrons and electrons in a bond>electrons in a bond and electrons in the other bond. Therefore, lone pairs of electrons around the central atoms will be arranged in such a way they are furtherest from each other and ...
- Sun Nov 24, 2019 7:58 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Explain VSEPR conceptually
- Replies: 12
- Views: 746
Re: Explain VSEPR conceptually
VSEPR gives the 3d shape and the bond angles within a molecule and is able to give us information in terms of the molecule's polarity and how lone pairs repulse each other, which cannot be given by simply looking at the lewis structure.
- Sun Nov 17, 2019 4:55 pm
- Forum: Dipole Moments
- Topic: dipole moments
- Replies: 2
- Views: 173
Re: dipole moments
You can determine the dipole moment by comparing the difference in electronegativity; the atom with a higher electronegativity is partially negative and the atom with a lower electronegativity is partially positive since its electrons are more attracted toward the other atom.
- Sun Nov 17, 2019 4:53 pm
- Forum: Dipole Moments
- Topic: London Forces
- Replies: 4
- Views: 199
Re: London Forces
All molecules have london dispersion forces because it is experimentally observed that the electron clouds in molecules are not fixed and tend to move around, which results in temporary dipole moments that create the london dispersion forces in neighboring molecules.
- Sun Nov 17, 2019 4:52 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: 2E.19 b
- Replies: 2
- Views: 135
Re: 2E.19 b
It is tetrahedral about the carbon atom but it is linear about the Be atom.
- Sun Nov 17, 2019 4:49 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: trigonal planar vs trigonal pyramidal
- Replies: 3
- Views: 180
Re: trigonal planar vs trigonal pyramidal
The lewis structures look the same because you can only draw them in a two-dimensional space but the VSEPR model depicts the shape in a three-dimensional space and illustrates the effect of repulsion by a lone pair, which results in a different shape and is not trigonal planar(has no lone pair).
- Sun Nov 17, 2019 4:43 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: geometric angles
- Replies: 4
- Views: 236
Re: geometric angles
The angles can only be determined experimentally but if there is no lone pair, each type of VSEPR structure has specific angles in between the bonds. To do this, you can only memorize the angles for more complex shapes such as tetrahedral... But for other shapes such as linear, the angles have to ad...
- Sun Nov 10, 2019 6:17 pm
- Forum: Dipole Moments
- Topic: Polarity
- Replies: 8
- Views: 205
Re: Polarity
It is polar if there is a difference in electronegativity since electrons are more pulled toward the one with the higher electronegativity, creating a charge.
- Sun Nov 10, 2019 6:15 pm
- Forum: Electronegativity
- Topic: Electron Affinity and Electronegativity
- Replies: 7
- Views: 383
Re: Electron Affinity and Electronegativity
Electron affinity is the energy difference between a ground state atom and after the atom gets an electron. Electronegativity is the tendency or an atom to attract electrons. These two terms have the same trend on the periodic table, but electronegativity can be seen as taking an average of both ion...
- Sun Nov 10, 2019 6:12 pm
- Forum: Dipole Moments
- Topic: HYDROGEN BONDING
- Replies: 3
- Views: 125
Re: HYDROGEN BONDING
Hydrogen bonding is another way of saying there is a strong dipole-dipole attraction between two molecules, but because the electronegativity between these atoms are larger than a normal dipole moment, we call them hydrogen bonding, which is the strongest intermolecular force.
- Sun Nov 10, 2019 6:09 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: Temporary vs. Permanent Dipole
- Replies: 3
- Views: 203
Re: Temporary vs. Permanent Dipole
Temporary dipole is when a molecule is not actually polar but because of the shifting electron clouds it creates a temporary dipole moment. Permanent dipole is formed when the difference electronegativity is large enough to allow the electronegative atom to constantly attract electrons from the othe...
- Sun Nov 10, 2019 6:07 pm
- Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
- Topic: London dispersion
- Replies: 4
- Views: 227
Re: London dispersion
All molecules have london dispersion forces because the electron clouds in a molecule is nit fixed and tend to shift around and give the molecule an instantaneous dipole moment that allow bonds to be formed in between. They are the weakest because these dipole moments are weak, unstable, and tempora...
- Sun Nov 03, 2019 5:08 pm
- Forum: Ionic & Covalent Bonds
- Topic: Ionic character in covalent bonds
- Replies: 3
- Views: 269
Re: Ionic character in covalent bonds
Covalent bonds can have increasing ionic character if there is a difference in the electronegativity between the two elements , which there always is between two different element. The larger the electronegativity, the larger difference in their ability to pull electrons to itself, which then become...
- Sun Nov 03, 2019 5:06 pm
- Forum: Dipole Moments
- Topic: Dipole moment
- Replies: 3
- Views: 181
Re: Dipole moment
If the covalent bond is between two different element then yes it is polar because having a dipole moment means the electrons are not equally shared and there is a difference between any two different element, large or small.
- Sun Nov 03, 2019 5:03 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: When would 3d orbital be filled before the 4s orbital?
- Replies: 8
- Views: 445
Re: When would 3d orbital be filled before the 4s orbital?
The 3d orbital will never be filled before the 4s orbital because any (n+1)s orbital is lower in energy than the nd orbital if there is no electron in the 3d orbital. However, after the 4s is filled and there is one electron in the 3d orbital, you would move the 3d orbital to the left of the 4s orbi...
- Sun Nov 03, 2019 4:55 pm
- Forum: Ionic & Covalent Bonds
- Topic: Drawing Ionic Compunds
- Replies: 7
- Views: 515
Re: Drawing Ionic Compunds
For example, if you are drawing the ionic compound NaCl, Na will have no dots around it because it lost its valence electron indicated by the +1 charge and chlorine will have 8 dots around it because it pulled the electron from Na to itself, indicated by the charge 1-. Then you would draw them separ...
- Sun Nov 03, 2019 4:52 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Highest energy level
- Replies: 1
- Views: 87
Re: Highest energy level
The highest energy level is told to be zero because this is the point where the electron is completely removed from the atom and no longer experiences any pull force from the atom. You can see this as an energy level that takes an infinitely large number such as 1*10^999, which if you insert it into...
- Sun Oct 27, 2019 8:32 pm
- Forum: Lewis Structures
- Topic: Lone Pairs
- Replies: 12
- Views: 515
Re: Lone Pairs
Lone pair electrons are just electrons that are not shared with another atom therefore just count the electrons that are not in between two atoms but instead only on the side of ONE atom.
- Sun Oct 27, 2019 8:30 pm
- Forum: Resonance Structures
- Topic: delocalized electrons
- Replies: 3
- Views: 144
Re: delocalized electrons
Delocalised electrons means that in a resonance structure, the electrons are not particularly associated with specific atoms in one specific location, they are instead conceptually distributed over various pairs of atoms and cannot be drawn with a stationary, one-dimensional Lewis structure since in...
- Sun Oct 27, 2019 8:25 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: 2A.15
- Replies: 3
- Views: 128
Re: 2A.15
To do this type of problem, you only need to know what makes an atom stable(full s and p orbital or lower energy) and know which atoms are metal(lose electrons) or nonmetal(gain electrons).
- Sun Oct 27, 2019 8:20 pm
- Forum: Octet Exceptions
- Topic: Expanded octet
- Replies: 3
- Views: 122
Re: Expanded octet
The expanded octet concept comes from the idea that normally we would consider the valence orbitals of an atom or the outermost shell of an atom can hold no more than 8 electrons. An expanded octet is then an atom that holds more than eight electrons in its outmost shell. Atoms in or after period 3 ...
- Sun Oct 27, 2019 8:12 pm
- Forum: Lewis Structures
- Topic: Drawing Lewis Structures
- Replies: 3
- Views: 165
Re: Drawing Lewis Structures
First you will need to determine how many valence electrons there are in each atom by looking at the periodic chart(their group number), which is more efficient than writing out its electron configuration to determine. Then you will need to arrange the electrons around the atoms in a clockwise manne...
- Sun Oct 20, 2019 10:07 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Magnetic Quantum Number
- Replies: 5
- Views: 207
Re: Magnetic Quantum Number
This tells you where the electron is (the orientation of the orbital in regard to the three axes, x, y and z)after knowing the location of the shell and shape of the sub shell. For example, 2p gives you the first two quantum number but to know which orbital of the three orbitals in p subshell the el...
- Sun Oct 20, 2019 9:54 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Pauli Exclusion Prinicple
- Replies: 3
- Views: 172
Re: Pauli Exclusion Prinicple
It states that no more than two electrons can exist in the same orbital and that if they do they have opposite spins. This is because of the property of electrons(the exact property is too complicated) in the quantum world makes them impossible to have the exact quantum state(same n, l, ml, ms). The...
- Sun Oct 20, 2019 9:39 pm
- Forum: Properties of Electrons
- Topic: Electron Configuration
- Replies: 4
- Views: 2121
Re: Electron Configuration
Normally, the order of electron-filling takes the following sequence: 1s 2s 2p 3s 3p 4s 3d.... However, when the electrons contain more than 20 electrons, that is, after potassium starting with scandium, the 4s orbital is complete and electrons start going into the 3d orbital but once there is elect...
- Sun Oct 20, 2019 9:27 pm
- Forum: Properties of Electrons
- Topic: Spin
- Replies: 5
- Views: 176
Re: Spin
It is a value or description of the electron from a quantum view. The spin of an electron is mainly determined by another electron that interacts with it and in the case of an electron in the atom, it would be arranged in a way so that it has the lowest energy possible. That being said, if an electr...
- Sun Oct 20, 2019 9:11 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Neon- electron configuration
- Replies: 3
- Views: 227
Re: Neon- electron configuration
This is so because Neon belongs to what we call the noble gas family in the periodic table(last column) and all the atoms in this family has the same electron configuration in which there is no unpaired electron and a full s and p orbital, which makes them extremely unstable and therefore unreactive.
- Sun Oct 13, 2019 2:49 pm
- Forum: DeBroglie Equation
- Topic: When to use DeBroglie Equation
- Replies: 16
- Views: 608
Re: When to use DeBroglie Equation
The De Broglie equation can be used with any object as long as you have the p=momentum of the object, therefore theoretically you can also use it with light because although photons don't have mass, they still have momentum, but in order to this you have to be given its momentum since you cannot cal...
- Sun Oct 13, 2019 2:40 pm
- Forum: Properties of Light
- Topic: Wave vs. Particle
- Replies: 4
- Views: 158
Re: Wave vs. Particle
The reason why we say light has both wave and particle properties is because it's experimentally proven. The diffraction patterns that shows up when certain wavelength of light passes through a crystal confirms its wave-like property. When conducting the photoelectric experiment, we notice that if t...
- Sun Oct 13, 2019 2:35 pm
- Forum: Properties of Electrons
- Topic: Balmer and Lyman Series
- Replies: 3
- Views: 240
Re: Balmer and Lyman Series
It makes sense to group them in this way because as you already saw during Dr. Lavelle's lecture, the energy difference between n=1 and any other level is the largest while the energy difference between n=2 and any other level is relatively smaller. This is the reason why a gap is observed on the em...
- Sun Oct 13, 2019 2:22 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Dilutions
- Replies: 10
- Views: 1018
Re: Dilutions
When you see this kind of problem, the first thing to do is to just calculate the molarity of the original solution. Since the question is asking how much volume is needed to obtain a certain amount of moles of sodium carbonate, the logic here would be what volume of the original solution would cont...
- Sun Oct 13, 2019 2:14 pm
- Forum: Significant Figures
- Topic: How many significant figures are in 7.00 x 10^2?
- Replies: 25
- Views: 3413
Re: How many significant figures are in 7.00 x 10^2?
It has 3 significant figures because when looking at significant figures in scientific notation, we only look at number on the left side, and since 7.00 has a decimal point, it has 3 significant figures. Another way to look at this is that this number is accurate to the hundredth place, so even if y...
- Mon Oct 07, 2019 10:03 pm
- Forum: SI Units, Unit Conversions
- Topic: Problem E.1
- Replies: 2
- Views: 218
Re: Problem E.1
Yes, it will be fine as long as you have the correct number of sig. fig. in your expression. An exception to this would be if the question explicitly asks you to express your answers in specific units.
- Mon Oct 07, 2019 9:59 pm
- Forum: Significant Figures
- Topic: Significant Figures and Molar Masses
- Replies: 5
- Views: 386
Re: Significant Figures and Molar Masses
Things that are constant such as molar masses should not be taken into consideration for sig. fig.. We normally determine the number of sig.fig. by looking at the number given by the question that has the least number of sig. fig..
- Mon Oct 07, 2019 9:52 pm
- Forum: Limiting Reactant Calculations
- Topic: Percent yield
- Replies: 3
- Views: 105
Re: Percent yield
The theoretical yield can be directly calculated by the number of moles of reactants given in the problem(or obtained from the grams used). You would use the mole-to-mole ratio in a balanced chemical equation to find out how many moles of products are produced and convert it into grams. This is call...
- Mon Oct 07, 2019 9:48 pm
- Forum: Balancing Chemical Reactions
- Topic: Fundamentals H.11
- Replies: 3
- Views: 131
Re: Fundamentals H.11
This is not always the case, you would want to write a new equation without putting any stoichiometric coefficients that you got from the first equation because these stoichiometric coefficients are unique relative mole numbers in chemical equations. The moles of products you got from the first equa...
- Mon Oct 07, 2019 9:30 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: G13
- Replies: 2
- Views: 278
Re: G13
One thing to keep in mind is that the moles of solute never change. So to find out how many moles of solute are in the solution, we multiply 0.2 M by 1.0, which indicates that there are 0.2 moles of ammonium nitrate molecules. In this case, you final volume would be 1 L + 3 L, Which equals to 4 L. D...
- Fri Sep 27, 2019 8:29 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Dilution
- Replies: 9
- Views: 503
Re: Dilution
Imagining you have a cup of water with five red beans in it. The solute is the red beans and the solvent is the water. To dilute this solution, we add water to the cup, however, the number of red beans remain unchanged and therefore the number of moles of solute remains unchanged; in this case, it's...
- Fri Sep 27, 2019 8:18 pm
- Forum: Accuracy, Precision, Mole, Other Definitions
- Topic: Figuring out the names of things
- Replies: 4
- Views: 269
Re: Figuring out the names of things
There is a formula for figuring out how to write the name of certain chemical compounds. In order to do this, we need to first put different chemical compounds into different categories. Binary compounds can be divided in to three categories, binary ionic compound, binary covalent compound, and bina...
- Fri Sep 27, 2019 7:34 pm
- Forum: Limiting Reactant Calculations
- Topic: Limiting Reagent
- Replies: 2
- Views: 123
Re: Limiting Reagent
Your previous steps are correct, so I will just answer what to do next. After getting the number of moles of each reactant, you should use stoichiometry to determine the number of moles of either one of the product produced. Let's say we choose NO(g) as the product that we will be using to compare t...
- Fri Sep 27, 2019 6:43 pm
- Forum: Empirical & Molecular Formulas
- Topic: Formulas
- Replies: 10
- Views: 2231
Re: Formulas
In order to find the number to multiply on a empirical formula to figure out the molecular formula, you must be given the molar mass of the compound and then divide it by the mass of the empirical formula you obtain to see the proportional relationship between them. If you get a number of 2, simply ...
- Fri Sep 27, 2019 6:38 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Questions about Homework Problem G5
- Replies: 3
- Views: 179
Re: Questions about Homework Problem G5
The reason that you need to multiply Na^+ by 2 is because in one molecule of Na2CO3, there are two Na^+ ions(which balances the negative 2 charge that CO3^2- ions carry), and so the number of sodium ions will always be 2X more than the number of Na2CO3, which means its molarity will also be 2X more ...