## Search found 60 matches

Tue Mar 12, 2019 5:25 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow or Fast Step
Replies: 3
Views: 162

### Re: Slow or Fast Step

Most often the slow step will be given to you. If it is not, you can look at the overall rate law, which usually represents the rate determining step (slow step).
Tue Mar 12, 2019 5:16 pm
Forum: First Order Reactions
Topic: Rate dependency
Replies: 5
Views: 222

### Re: Rate dependency

Also remember to look at the order of the reactants. If there rate order of a reactant is zero, then it is not dependent on the concentration, but rather k.
Tue Mar 12, 2019 5:13 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: molecularity
Replies: 3
Views: 155

### Re: molecularity

You can find the molecularity of a reaction by looking at the rate determining step, or slow step. The overall rate law if the rate law of the slow step, since this step determine the rate of the reaction. If there are two molecules reacting, then it is bimolecular. If there is three, then it is ter...
Tue Mar 12, 2019 5:10 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: order of a cell diagram
Replies: 4
Views: 174

### Re: order of a cell diagram

If there are coefficients in the half reactions, you do not need to include them. Just remember to separate the phases with a bar and the two half reactions with a double bar.
Tue Mar 12, 2019 5:04 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow vs Fast Step
Replies: 4
Views: 162

### Re: Slow vs Fast Step

If the slow step is the not first step and contains and intermediate, you can assume the first step is at equilibrium and use the pre-equilibrium approach.
Fri Mar 08, 2019 3:36 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Rate Order Graphs
Replies: 3
Views: 171

### Re: Rate Order Graphs

If you are only given the reactant concentrations and their respective times, you can use graphs to determine the order of each reactant. For example, if the graph of ln[A] vs. time is linear, it is first order. In addition, if [A] vs. time is linear, then it is zero order.
Fri Mar 08, 2019 3:32 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow step
Replies: 4
Views: 168

### Re: Slow step

The addition, the slow step should not contain an intermediate as one of its reactants since it cannot appear in the rate law.
Mon Mar 04, 2019 11:39 am
Forum: Balancing Redox Reactions
Topic: Cell diagrams
Replies: 8
Views: 263

### Re: Cell diagrams

That is correct. The only exception for liquids is mercury liquid, which is a good conductor of electricity. Therefore, if mercury liquid is present, you do not need to add Pt.
Mon Mar 04, 2019 11:37 am
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Replies: 73
Views: 3817

Try doing all of the homework practice questions. I found doing this to be very helpful. By doing this, you can gauge your strengths and weaknesses and subsequently attend office hours or workshops to clarify any questions you may have.
Mon Mar 04, 2019 11:34 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Nernst Equation
Replies: 4
Views: 143

### Re: Nernst Equation

Use the information that you have to solve for a certain desired variable. Because many of the values in the Nernst equation are constants, you usually only need to find one or two more values.
Mon Mar 04, 2019 11:29 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: van't hoff equation
Replies: 6
Views: 256

### Re: van't hoff equation

Use the base e and raise it to the value on the right hand side of the equation (-delta H/R*(1/T2-1/T1)). Then isolate the variable K2 to determine the value.
Mon Mar 04, 2019 11:25 am
Forum: Van't Hoff Equation
Topic: K value- Temp
Replies: 6
Views: 472

### Re: K value- Temp

In addition, in order to use the equation stated above, you must assume that delta H and delta S are constant. This equation allows us to determine K at different temperatures is these values (delta H and delta S) are known.
Sun Feb 17, 2019 4:59 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Temperature
Replies: 2
Views: 101

### Re: Temperature

More information must be given in order to determine whether a process will proceed in the forward or reverse direction. The change in enthalpy by the reaction is particularly important as you can determine whether the reaction is endothermic or exothermic.
Sun Feb 17, 2019 4:54 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: DeltaS= nCln(T2/T1)
Replies: 4
Views: 220

### Re: DeltaS= nCln(T2/T1)

Always look at the context of the question. If you are having trouble determining which one is constant, go back to the basics. Like stated above, sometimes you may have to split the entropy change into several steps, which works since entropy is a state function.
Sun Feb 17, 2019 4:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Bond Enthalpies
Replies: 8
Views: 322

### Re: Bond Enthalpies

In addition, this method is the least accurate because we are calculating the average bond enthalpies of each bond from different molecules. Therefore, there will always be some error in the final value.
Sun Feb 17, 2019 4:41 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible v irreversible
Replies: 4
Views: 448

### Re: Reversible v irreversible

To add, reversible reactions always result in more work because of the infinitesimally pressure differences.
Sun Feb 17, 2019 4:37 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibbs Free Energy Definition
Replies: 4
Views: 129

### Re: Gibbs Free Energy Definition

Gibbs free is energy is energy available to do work. You can think of it as enthalpy being the total amount of energy and T times delta S (TΔS) being the energy that is lost to entropy. Thus, change in Gibbs free energy is equal to change in enthalpy minus TΔS (ΔG = ΔH – TΔS).
Sun Feb 17, 2019 4:33 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Positive Gibbs Free Energy
Replies: 3
Views: 134

### Re: Positive Gibbs Free Energy

Reactions with a positive Gibbs free energy are usually carried out with accompaniment of another reaction. This is called a coupled reaction, and it allows the overall process to occur. An example is ATP hydrolysis, in which ATP is used to carry out the main reaction.
Sun Feb 03, 2019 4:40 pm
Forum: Calculating Work of Expansion
Topic: internal vs. external pressure
Replies: 3
Views: 1038

### Re: internal vs. external pressure

Internal pressure is how much change in energy a system undergoes when it expands or contracts. External pressure is the amount of energy that is applied from the outside. At equilibrium, these two are equal
Sun Feb 03, 2019 4:30 pm
Forum: Calculating Work of Expansion
Topic: What is Work?
Replies: 5
Views: 164

### Re: What is Work?

Work is the transfer of mechanical energy between two systems and is measured in Joules. In other words, it is the energy transferred by a system to its surroundings.
Sat Feb 02, 2019 5:46 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: bond enthalpy equations
Replies: 6
Views: 196

### Re: bond enthalpy equations

Bond enthalpy is defined as the amount of energy required to break a bond. You can calculate bond enthalpy of a reaction by subtracting the total bond enthalpies of products from the total bond enthalpies of reactants.
Sat Jan 26, 2019 11:27 am
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: heat capacity
Replies: 7
Views: 314

### Re: heat capacity

Heat capacity allows us to quantify a substance's ability to absorb heat energy. It is also important to note the difference between heat capacity and specific heat, as specific heat focuses solely on one unit of mass.
Sat Jan 26, 2019 11:20 am
Forum: Phase Changes & Related Calculations
Topic: Severe burn from steam clarification
Replies: 5
Views: 1602

### Re: Severe burn from steam clarification

To add, steam is a lot more severe than boiling water because it has more heat energy than water. An immense amount of energy is released when steam hits your skin and condenses into a liquid.
Fri Jan 25, 2019 3:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: What not to count
Replies: 9
Views: 356

### Re: What not to count

If you are talking about salt solutions, then you must disregard ions that fully dissociate because they do not affect the pH of the solution. For example, cations of strong bases do not affect pH because they fully dissociate. The same applies to anions of strong acids.
Thu Jan 17, 2019 9:54 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: when is x negligible
Replies: 7
Views: 1654

### Re: when is x negligible

[OH-] is equal to [H30+] when the pH of the solution is neutral. Kw is always 1 x 10^-14 at 25 C.
Thu Jan 17, 2019 9:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Quadratic equation and ICE box
Replies: 3
Views: 76

### Re: Quadratic equation and ICE box

If you are given a K value that is less than 10^-3 and end up with x variables that are cubed (or higher), you can use the approximation that was shown in class. Although you can use approximations for quadratic equations as well, it is safer to use the quadratic formula to obtain a more accurate an...
Thu Jan 17, 2019 9:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: ICE box
Replies: 2
Views: 118

### Re: ICE box

Yes, that is correct. Try to use what is given to you in the question. If there is no product, assume that the reaction will shift to the right.
Sun Jan 13, 2019 1:44 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kc and Kp
Replies: 5
Views: 166

### Re: Kc and Kp

You use Kc or Kp based on the information that is given and what the question is asking for. For example, if you are given gases and their molar concentrations, you can use Kc. However, if the question requires you to calculate Kp, use the Ideal Gas Law to convert Kc to Kp.
Sun Jan 13, 2019 1:38 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: (aq) in calculating K
Replies: 9
Views: 218

### Re: (aq) in calculating K

When calculating K, we do not consider pure liquids and solids because we are only interested in things that are changing. Pure solids remain constant and liquids like water are too excessive to consider.
Sun Jan 13, 2019 1:33 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equations
Replies: 6
Views: 223

### Re: Equations

When you are given equilibrium concentrations, you must use Kc to calculate the equilibrium constant. This can apply to both aqueous solutions and gases. In contrast, Kp can only be used to calculate the equilibrium constant of partial pressures. Kp cannot be applied to aqueous solutions since they ...
Fri Dec 07, 2018 1:32 am
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Are all pH calculations done to 2 decimal places or do we use sig figs in pH calculations? [ENDORSED]
Replies: 2
Views: 189

### Re: Are all pH calculations done to 2 decimal places or do we use sig figs in pH calculations?[ENDORSED]

For pH calculations, the sig figs are only accounted for after the decimal point. In this case, since there are two sig figs in 0.0092 M Ba(OH)2, the final answer should present two digits after the decimal point. Thus, 12.96 is correct.
Fri Dec 07, 2018 1:29 am
Forum: Lewis Structures
Topic: Valence electrons
Replies: 2
Views: 111

### Re: Valence electrons

The valence electrons are the electrons in the outermost energy level. In this case, the elements in the d block will have valence electrons in the s block. For example, the element Mn will have its valence electron in the 4s orbital.
Fri Dec 07, 2018 1:20 am
Forum: Amphoteric Compounds
Topic: Amphiprotic vs. amphoteric
Replies: 3
Views: 181

### Re: Amphiprotic vs. amphoteric

Amphoteric compounds are essentially any compound that can act as an acid or base. Amphiprotic compounds are also amphoteric compounds, but more specially refer to compounds having the ability to either donate or accept a proton.
Fri Dec 07, 2018 1:12 am
Forum: Determining Molecular Shape (VSEPR)
Topic: H-bonds
Replies: 4
Views: 192

### Re: H-bonds

Hydrogen bonds are strong dipole-dipole forces that result from polar bonds within a molecule. When an N, O, or F atom is bonded to H, the molecule becomes extremely polar due to the high electronegativity difference.
Fri Dec 07, 2018 1:01 am
Forum: Shape, Structure, Coordination Number, Ligands
Topic: Coordination Complexes
Replies: 2
Views: 72

### Coordination Complexes

What is the difference between a tetrahedral complex and a square planar complex?
Sun Dec 02, 2018 4:33 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: Final pH
Replies: 3
Views: 109

### Re: Final pH

You can use the formula pH + pOH = 14 for any aqueous solution. The "p" essentially means to take the negative logarithm of a value. To solve for either pH or pOH, plug in the given values to obtain a certain variable.
Sun Dec 02, 2018 4:20 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Chemical Bonds of Nonmetals
Replies: 2
Views: 179

### Re: Chemical Bonds of Nonmetals

Nonmetals rarely lose electrons and therefore it is common for them to gain electrons and form anions, as their electronegativities are very high.
Sun Nov 25, 2018 7:46 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: Dipole-Dipole forces
Replies: 3
Views: 165

### Re: Dipole-Dipole forces

This is not the only way. Nonpolar molecules can have dipole-dipole forces as well, only the dipoles cancel each other out. Therefore, it is important to look at the overall structure of the molecule and their respective dipole moments.
Sun Nov 25, 2018 7:42 pm
Forum: Properties of Light
Topic: Speed of light
Replies: 13
Views: 3206

### Re: Speed of light

Just to be safe, you should use the constant given on the formula sheet. Otherwise, ask your TA for their preference.
Sun Nov 25, 2018 7:40 pm
Forum: Lewis Acids & Bases
Topic: How do we know something is a lewis acid or base?
Replies: 4
Views: 273

### Re: How do we know something is a lewis acid or base?

It is helpful to draw the Lewis structure of the molecule when determining whether something is a Lewis base or acid. For example, if there is a lone pair on a central atom in a molecule, the molecule is mostly likely a Lewis base because it can donate those electrons to an acid.
Thu Nov 15, 2018 11:07 pm
Forum: Ionic & Covalent Bonds
Topic: H bonds and melting points
Replies: 4
Views: 209

### Re: H bonds and melting points

In addition, hydrogen bonds are so strong because of the intermolecular forces between polar molecules. These forces are especially stronger due to the bonds between hydrogen and atoms with high electronegativity (i.e. N, O, and F).
Thu Nov 15, 2018 10:55 pm
Forum: Ionic & Covalent Bonds
Topic: Polar/non polar molecules
Replies: 5
Views: 230

### Re: Polar/non polar molecules

You can determine if a molecule is polar or nonpolar based on its shape. For example, if the shape of the molecule is symmetric and it presents an even distribution of electron densities, then it is most likely nonpolar (and vice versa).
Sun Nov 11, 2018 5:39 pm
Forum: Lewis Structures
Topic: Exceptions to Octet Rule
Replies: 5
Views: 302

### Re: Exceptions to Octet Rule

Although elements in period 3 and beyond have an expanded octet (due to their ability to access their d orbital), it does not necessarily mean that they don't obey the octet rule. It is always best to assign each element an octet when drawing Lewis structures and to determine the best and most stabl...
Sun Nov 11, 2018 5:35 pm
Forum: Bond Lengths & Energies
Topic: bond energy
Replies: 4
Views: 163

### Re: bond energy

The bond energy between atoms is usually given in the problem. You can therefore use the information given to isolate a certain variable and determine its bond energy. However, it is good to know that double and triple bonds have significantly greater bond energies than single bonds.
Sun Nov 11, 2018 5:31 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: Intermolecular Forces
Replies: 4
Views: 152

### Re: Intermolecular Forces

Yes, Van der Waals forces and London dispersion forces are used interchangeably and are therefore the same strength. They are the weakest intermolecular forces between molecules.
Thu Nov 01, 2018 10:57 pm
Forum: Ionic & Covalent Bonds
Topic: Copper Ions
Replies: 3
Views: 117

### Re: Copper Ions

As anions, copper II loses one more electron than copper I since their forms are Cu2+ and Cu1+, respectively.
Thu Nov 01, 2018 10:52 pm
Forum: Ionic & Covalent Bonds
Topic: Electron Configuration
Replies: 3
Views: 125

### Re: Electron Configuration

A more conventional way to write the electron configuration of Br is [Ar] 4s2 3d10 4p5 since the 4s subshell is filled first. However, either is correct.
Thu Nov 01, 2018 10:31 pm
Forum: Lewis Structures
Topic: d orbitals in valence shell that accommodate additional e-
Replies: 2
Views: 53

### Re: d orbitals in valence shell that accommodate additional e-

Only elements with orbitals higher than p can have more than the octet because of the additional space. The s and p orbitals can only hold 8 electrons in total.
Fri Oct 26, 2018 9:10 pm
Forum: Ionic & Covalent Bonds
Topic: Valence Electrons
Replies: 3
Views: 142

### Re: Valence Electrons

The elements are held together by electrostatic attractions. In the case of ionic bonds, the atoms are attracted to one another due to their opposite charges.
Thu Oct 25, 2018 9:31 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Ionization Energy
Replies: 3
Views: 147

### Re: Ionization Energy

Yes, that is correct. The same concept can be applied to halogens, which require one more electron to complete an octet.
Thu Oct 25, 2018 2:24 pm
Forum: Einstein Equation
Topic: E=hv
Replies: 43
Views: 4454

### Re: E=hv

The value E represents the energy of the photon. However, you can use the equation E=hv to calculate the energy required to remove an electron after taking into account the kinetic energy. This works because the energy of the photon must be greater than or equal to the energy required to remove the ...
Thu Oct 18, 2018 3:44 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Bohr condition explaining lines
Replies: 2
Views: 141

### Re: Bohr condition explaining lines

Bohr's model shows that electrons move from one orbit to another based on whether or not the energy of the photons is equivalent to the energy difference between the orbits. Thus, the spectral line is essentially a representation of this condition.
Thu Oct 18, 2018 3:35 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Atomic Spectroscopy vs Molecular Spectroscopy
Replies: 2
Views: 137

### Re: Atomic Spectroscopy vs Molecular Spectroscopy

Atomic spectroscopy studies how electromagnetic energy is absorbed or emitted by atoms. Molecular spectroscopy studies the interactions of both atoms and molecules. Therefore, molecular spectroscopy is much more comprehensive as it provides more information about certain characteristics.
Thu Oct 18, 2018 3:18 pm
Forum: Trends in The Periodic Table
Topic: Period Table 'blocks'
Replies: 5
Views: 154

### Re: Period Table 'blocks'

Blocks are essentially a simple way to categorize elements into their respective orbital. These categories are determined by the highest energy electrons.
Thu Oct 11, 2018 12:26 pm
Forum: Trends in The Periodic Table
Replies: 2
Views: 194

The radius of an atom is the distance from the center of the nucleus to the edge of the farthest electron cloud. A covalent radius is formed when two of the same elements are covalently bonded to one another. This radius can be determined using half of the distance between the two nuclei. Lastly, an...
Thu Oct 11, 2018 12:15 pm
Forum: SI Units, Unit Conversions
Topic: Atoms and Molecules
Replies: 5
Views: 171

### Re: Atoms and Molecules

It really depends on the context of the problem. If the question is asking you to find the number of atoms or ions in a specific molecule, remember to multiply the number of moles appropriately.
Thu Oct 11, 2018 12:11 am
Forum: SI Units, Unit Conversions
Topic: Should Significant Figures be affected by constants?
Replies: 10
Views: 382

### Re: Should Significant Figures be affected by constants?

The significant figures in your final answer should not be affected by the number of sig figs in your constants. Simply put, apply the sig figs rules based on the number of sig figs of the variable given to you in the problem. In your case, your final answer should be 5.86957 x 10^-7 m since 6 sig f...
Thu Oct 04, 2018 4:08 pm
Forum: Molarity, Solutions, Dilutions
Topic: Problem G5
Replies: 8
Views: 368

### Re: Problem G5

Yes, in this case we are using the M1V1=M2V2 formula. M1V1 is equal to the number of moles of Na2CO3, which is 1.08 x 10^-3 mol. You then set this equal to M2V2. M2 can be calculated using the given number of grams of Na2CO3 (2.111g) and volume (250.0mL). With this information, you set the equations...
Thu Oct 04, 2018 3:01 pm
Forum: SI Units, Unit Conversions
Topic: mol vs. mmol
Replies: 12
Views: 837

### mol vs. mmol

What is a mmol? In some of the practice questions in G we are given the unit mmol.
Thu Oct 04, 2018 2:45 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Molecules vs Formula Units? E21
Replies: 2
Views: 87

### Re: Molecules vs Formula Units? E21

There is essentially no difference when calculating for molecules and formula units. Formula units are used for ionic compounds and molecules are used for covalent bonds.