CHEMISTRY COMMUNITY

Brian Chang 2H

Temperature affects the rate constant.

Brian Chang 2H

The unit for rate constant (k) in second-order reactions is (1/Mol*s).

Brian Chang 2H

That's perfectly fine.

The total order of the reaction is calculated by summing up the exponents the individual reactants. (1+1=2)

Brian Chang 2H

The final will be on ALL topics covered this quarter. Study the syllabus in its totality.

Brian Chang 2H

The Haber process is an example of a 0th order rxn.

Brian Chang 2H

It's technically included, but since it is raised to the 0th power it just becomes 1.

Brian Chang 2H

0th order reactions are time vs concentration.
1st order reactions are time vs ln(concentration).
2nd order reactions are time vs 1/concentration.

Brian Chang 2H

When we talk about half-life, does this imply that there is normal life? I'm confused about what half-life is and when we would want to calculate it? Half-life is defined as the time taken for the radioactivity of a specified isotope to fall to half its original value. Simply put, it's the time tak...

Brian Chang 2H

Fionna Shue 4L wrote:Can 2A -> B + C be a first order reaction and why?

It CAN be first order, but doesn't necessarily have to be.

Reaction orders are determined experimentally and are not related to stoichiometric coefficients.

Brian Chang 2H

There are zero order reactions in real life (ie. the Haber Process).

Typically occurs when reactants are already in large excess.

Brian Chang 2H

If you have m and n you can plug them in to find K,

similarly, you can use k to derive either m or n.

You CANNOT solve for more than 1 unknown though.

Brian Chang 2H

Unique rate is just the "normal rate" of formation of a product, multiplied by the negative inverse of its stoichiometric coefficient.

Brian Chang 2H

Unique rates are always divided by the stoichiometric coefficients of either the reactant/product in question. The instantaneous rate is determined by calculating the slope of the graph of concentration over time. Instantaneous unique rate is determined by the instantaneous rate of change in the con...

Brian Chang 2H

Reaction rate doesn't take into account stochiometric coefficients but unique reaction rate (specific to each reactant/product) does.

Brian Chang 2H

The slow step will either be explicitly referred to as the "Slow step" or it will be implicit by having a lower k value than the other steps. Indicating that it is the slowest step.

Brian Chang 2H

If you can find a course reader (or a scan of one) there are very helpful past paper questions included inside.

Brian Chang 2H

I would personally focus on practical application instead of rote memorization.

Most of the equations we need are on the formula sheet. The rest can be (almost) always be derived.

Brian Chang 2H

A system is typically expanding when it is doing work.

This is usually denoted by a negative (w) value as work is being done BY the system, so therefore energy is leaving the system.

Brian Chang 2H

Cp,m refers to an ideal gas at constant pressure (C. P. = Constant Pressure).

Cv,m refers to an ideal gas at constant volume (C. V. = Constant Volume).

Brian Chang 2H

Extensive properties depend on how much of a substance is present. (Ie. the mass of the sample is dependent on how much there is.)

Intensive properties are independent of the amount of substance present. (Ie. Water boils at 100 degrees Celcius regardless of the amount, be it 1L or 10L.)

Brian Chang 2H

Adiabatic: relating to or denoting a process or condition in which heat does not enter or leave the system concerned.

Isothermal: No change in temp, so delta T = 0.

Brian Chang 2H

The system is the "reaction" that you're observing, typically in a piston or some form of enclosed chamber. (Unless it's an open system)

The surroundings are just everything else.

Brian Chang 2H

Extensive properties are tied to external factors (such as mass and volume), whereas intensive properties (hardness, colour, boiling point) do not change with the amount of substance.

Brian Chang 2H

Think of thermal equilibrium like chemical equilibrium. We say that a solution is at equilibrium when the rate of the forward reaction is equal to the rate of the backward reaction. Similarly, we say that a system is at thermal equilibrium when the energy (heat) lost to the surroundings is the same ...

Brian Chang 2H

An open system facilitates the exchange of both energy and matter.
A closed system facilitates the exchange of energy, but not the exchange of matter.
An isolated system facilitates the exchange of neither energy nor matter.

Brian Chang 2H

A closed system does not allow the exchange of matter but allows the exchange of energy.

An isolated system does not allow the exchange of energy nor matter.

Brian Chang 2H

It's impossible to create a perfect system, as this would mean that no energy is gained from or lost to the surroundings. Take heat for example. Heat can be transferred through conduction, convection, and radiation. A vacuum sealed flask can prevent the first two methods of transference, but radiati...

Brian Chang 2H

Not necessarily. SHC is just the heat capacity of a substance divided by its mass (in grams).

Molar heat capacity would be more accurate if you were concerned about the number of atoms being heated, but intermolecular forces have a much greater effect on the enthalpies of vaporization and such.

Brian Chang 2H

Heat Capacity is the amount of energy required to increase the temperature of a substance by 1-degree Celcius. Specific heat capacity is the amount of energy required to raise 1g or 1mol of a substance by 1-degree Celcius. Enthalpy is the measure of (heat) energy in a system. A reaction can be exoth...

Brian Chang 2H

Cv is for constant volume.
Cp is for constant pressure.

Brian Chang 2H

Solids and liquids are not included in Kc and Kp.

Because (a) their pure and don't have concentrations, and (b) they don't have partial pressures.

Brian Chang 2H

Theoretically yes?

But I agree with the comment above. It's unlikely something like this would come out.

Brian Chang 2H

As long as K < 10^-3 we can approximate. But do check if the final concentration is less than 5% to make sure that your approximation was justified.

Brian Chang 2H

ICE charts are useful when working with weak acids which only partially dissociate in solution.

Brian Chang 2H

Deprotonated means that the molecule/compound has lost a proton. (ie. (H20) -> (H+) + (OH-))

Ionized can mean either the loss or gain of an electron pair, so the molecule/compound becomes charged .

Brian Chang 2H

Q is the reaction quotient which can be at any time.
K is the equilibrium constant (only at equilibrium, duh.)
If Q > K then the reverse reaction is favoured.
If Q < K then the forward reaction is favoured.

Basically, it tells us which direction the reaction sits.

Brian Chang 2H

Use Kelvin.

The Gas Constant is in Kelvin so we have to use the same measurement for temperature.

To get Kelvin, just add 273.15 to your Celcius measurement.

Brian Chang 2H

PV=nRT is used to convert between concentration and partial pressure (for your Kc and Kp calculations).

The symbols represent P= Pressure, V=Volume, n= Number of Moles, R= Gas Constant, T= Temperature

Brian Chang 2H

K=1 means that AT EQUILIBRIUM the rate at which the forward reaction and backward reaction occur are equal.

This is rare because, in the real world, reaction rates can differ greatly, hence, it's unlikely that they'll just end up at 1.

Brian Chang 2H

Retweet^

Brian Chang 2H

It's actually the configuration according to math.

The electron domains themselves don't look like bubbles, it's just a representation of the regions in which electrons can/do be found.

TL/DR: It really do be like that.

Study Hard!

Brian Chang 2H

In all honesty, there are only 2 tricky bits to shapes.

1. Tetrahedral angles are 109.5 degrees (Not intuitive like everything else is.)

2. For shapes with 5 regions of electron density, lone pairs are placed along the equatorial plane first instead of the axial plane.

Brian Chang 2H

For the purposes of this midterm? Yes.

Brian Chang 2H

Hello everyone, I'm struggling a bit with this concept. In the hw, it told us to find the ground state of elements (ex: Bi which has 83 electrons) and then the answer was [Xe]4f^(14)5d^(10)6s^(2)6p^(3). When it comes to elements with a high number of electrons is there another way to go about this ...

Brian Chang 2H

Honestly, just balance everything as you normally would and where the formal charge ends up is probably right. There is no hard and fast rule for which element gets the formal charge because it depends how you balance the structure.

Brian Chang 2H

Polarity is often linked with Symmetry. CH4 is a tetrahedral molecule so it's charge is nicely balanced out between the 4 H atoms. But H2O is bent because Oxygen has 2 bonding pairs and two lone pairs. So the lone side of the molecule is more negatively charged than the side with Hydrogen atoms. So ...

Brian Chang 2H

Technically any element in the 3rd row and beyond has access to their d-orbitals, but we only really see elements in group 15,16, and 17 do this because it's highly unlikely for elements like Boron, Aluminium, or Gallium to ever have an expanded octet.

Cheers.

Brian Chang 2H

I just had a question. For Ionic and Covalent bonds would it be specifically one or would it be more accurate to say its one a spectrum? For example a Bond would have more ionic properties than covalent? Bonding is a spectrum where ionic is "giving" and covalent is "sharing" and...

Brian Chang 2H

As a rule, we always try to get formal charge as close to zero as possible so place the radical based on that.

If everything is zero then just pick one (Try to follow the octet guideline, dont give it to any elements with a full octet that isn't in group 3 as they can't take more than 8.)

Brian Chang 2H

Technically, any element in the 3rd row of the periodic table (and beyond) can form an expanded octet. Realistically, we only see it for the p-block elements in the 3rd row and beyond. (Ie. P, S, CL) This is because elements in the 3rd have access to the 3-d-orbitals so they can have more than 8 ele...

Brian Chang 2H

Formal charges can be annotated on the top right of your element symbol (ie. H, C, O). (There's not fixed position but I feel like this is the neatest way to display it. Just like normal charges and powers.)

Brian Chang 2H

N refers to shell
l refers to subshell
ml is the magnetic quantum number, but it indicates orientation.
ms indicates spin(+1/2 and -1/2)

Brian Chang 2H

The 2s orbital shields the 2p orbitals from the electronegative attraction of the nucleus.

Brian Chang 2H

A nodal plane is where there is zero electron density (no electrons there).

Brian Chang 2H

The possible orbitals are determined by the quantum number (n) with the formula l=n-1 (for the upper limit) and 0 at the lower limit.

Where, l=0 is an s-orbital
l=1 is a p-orbital
l=2 is a d-orbital
l=3 is a f-orbital

Brian Chang 2H

The 5 d-orbitals are : dxy, dyz, dzx, d(x^2-y^2), and dz^2.

Brian Chang 2H

All you need to know is.

Shell Numbers: Eg. n=1,n=2,n=3

Angular Momentum Number: Eg. l=0,l=1,l=2

Magnetic Quantum Number: Eg. ml=l,ml=l-1,ml=1+1

and then spins: either +(1/2) OR -(1/2)

Hope this helps!

Brian Chang 2H

Because S-Orbitals are spherical they have complete symmetry, hence there are no nodal planes.

Brian Chang 2H

TL:DR

Constructive interference is when the wave crests are in sync thereby creating waves of higher amplitudes.

Destructive interference occurs when the wave crests are out of sync, thereby creating waves of lower amplitudes.

Brian Chang 2H

E is the energy of light, which is measured in photons. A photon is the quantum of electromagnetic radiation.

Brian Chang 2H

C represents the Speed of Light, which is 2.99*10^8 m/s.

Brian Chang 2H

Most if not all elements exist in different forms. Only Protons and Electrons affect the charge of the atom whereas Neutrons can be added and only affect the weight of the atom. For example, Carbon exists in C-8 to C-15 isotopes where the only thing that changes is the number of Neutrons.

Brian Chang 2H

retweet ^

Brian Chang 2H

always use the number of sig figs of the number with the lowest number of sig figs in the question and subsequent calculations The number of sig figs will be determined by the number with the lowest sig figs in the equation. Eg. 3.28 + 1.5 = 4.8. (2 sig figs cause of 1.5) But, when dealing with more...

Brian Chang 2H

There is no trick to learning how to name compounds, however within organic and inorganic Chemistry the usual suspects will occur frequently such as Potassium Permanganate (KMnO4) and you should eventually be able to identify them with ease as long as you keep practicing!

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