CHEMISTRY COMMUNITY

Yiting_Gong_4L

when working with rate laws, you should be using concentration.
given grams of a substance and volume you can solve for the M which is concentration to plug into rate laws.

Yiting_Gong_4L

Half life is used to determine the time it takes for a substance to decompose into half its initial amount.

Yiting_Gong_4L

The negative order means that the rate is being decreased instead of the normal increasing rate (positive order).

Yiting_Gong_4L

the rate constant, k, will always be positive!

Yiting_Gong_4L

It is the same k as long as you use the same products and reactants because the numbers they give are under the same temp.

Yiting_Gong_4L

anode ll cathode

Yiting_Gong_4L

depending on what is given you will use different equations to solve for deltaG.

Yiting_Gong_4L

you use Van't Hoff when you are trying to relate a K value to the increasing temperature T.

Yiting_Gong_4L

The problem will specify whether the reaction occurs in basic or acidic solution. Depending on where the reaction takes place you use OH or H20 to balance oxygen and hydrogen.

Yiting_Gong_4L

E^ocell just means the cell potential at standard state. Ecell is the nonstandard state conditions.

Yiting_Gong_4L

Yes, there is a difference. Being oxidized means that molecule is the reducing agent. Being reduced means that the molecule is the oxidizing agent.

Yiting_Gong_4L

what is being reduced is the oxidizing agent and what is being oxidized is the reducing agent.

Yiting_Gong_4L

we probably don't need to know how to draw a galvanic cell.

Yiting_Gong_4L

the salt bridge and porous disk have the same function which is to balance out both sides of the beaker with salts. salt bridges are represented with two lines and porous only has one.

Yiting_Gong_4L

Gibbs free energy is the energy that is available to do work, unlike entropy/enthalpy/temperature, it cannot be directly measured.

Yiting_Gong_4L

system is the object, and surrounding is everything around it that can apply heat to it or lose heat.

Yiting_Gong_4L

You mean test 2? test 3 will not include gibbs free energy, but test 2 will.

Yiting_Gong_4L

It is probably best to understand the heat curve and how to apply it to questions.

Yiting_Gong_4L

Closed systems and isolated systems are two different types of systems.

Yiting_Gong_4L

Delta U is the change in internal energy. If it is positive that means the internal energy is increasing while a negative means decreasing.

Yiting_Gong_4L

A closed system is where substance can’t be added or removed, but heat can still be transferred in and out. An isolated system is where heat can not be transferred.

Yiting_Gong_4L

The Qsystem and Qsurrounding cancel out for the system to be perfect. Therefore the equation would equal 0.

Yiting_Gong_4L

Heat capacity is an extensive property, while specific heat is an intensive property.

Yiting_Gong_4L

Delta H is the change in enthalpy.

Yiting_Gong_4L

As long as you follow the units in the question you should be fine!

Yiting_Gong_4L

Exothermic reactions release energy, delta H is negative, and heat is a product. Endothermic reactions absorb energy, delta H is positive, and heat is a reactant.

Yiting_Gong_4L

K is the constant at equilibrium while Q is approaching the equilibrium. Solving for Q and comparing it to the K constant can get you the direction in which the reaction is favoring.

Yiting_Gong_4L

the question will tell you when to use Kc or Kp

Yiting_Gong_4L

When the reaction is exothermic that means heat is being released as a product. If you are lowering the temperature you are essentially removing heat and that means the reaction will favor the product.

Yiting_Gong_4L

Kp has to do with the partial pressure while Kc is the concentration.

Yiting_Gong_4L

water is omitted because it is a liquid. solids and liquids do not affect the equilibrium.

Yiting_Gong_4L

sits to the left - rxn favors reactants
sits to the right - rxn favors products

Yiting_Gong_4L

The temperature must stay the same in order for the equilibrium constant to stay the same.

Yiting_Gong_4L

The aqueous solution is still included in the calculation for K. Only solids and liquids are ignored.

Yiting_Gong_4L

K is the constant at equilibrium, Q is the reaction quotient which means the constant when it is not yet at equilibrium.
However, Q and K can be compared to find which reaction is favored (forward or reverse).

Yiting_Gong_4L

Kp and Kc both give the equilibrium constant, but Kp is for partial pressure and Kc is for concentration.

Yiting_Gong_4L

Solids and liquids are NOT included when calculating the equilibrium constant because a solids concentration would be 100% which is just 1 and doesn't affect the answer.
Only aqueous solutions and gases are included in the calculation of the equilibrium constant.

Yiting_Gong_4L

ICE tables can be used for concentration or partial pressure!

Yiting_Gong_4L

sigma bonds are stronger because the overlap of the sigma bond is smaller than the pi bond so it is harder to break apart.

Yiting_Gong_4L

yes the trends are the same!

Yiting_Gong_4L

The hybridization depends on the amount of electron densitys. (ex: lone pairs, bonds, etc.)

Yiting_Gong_4L

It is better to check the symmetry of the lewis structure.

Yiting_Gong_4L

Bond angles are determined by finding out the geometry of the molecule first. (Linear, Tetrahedral, Trigonal Pyramidal etc.) There are helpful charts online!

Yiting_Gong_4L

Yiting_Gong_4L

Single Bond: 1 sigma bond
Double Bond: 1 sigma bond + 1 pi bond
Triple bond: 1 sigma bond + 2 pi bonds

Yiting_Gong_4L

I dont think we are responsible for drawing the hybridization on the test.

Yiting_Gong_4L

a radical is still treated as a electron density in VSEPR.

Yiting_Gong_4L

The order for hybridization does not matter, but it does for electron configuration!

Yiting_Gong_4L

hybridzation depends on the number of regions of electron density. since there is 4 regions (1 lone pair and 3 atoms) the hybridization would be s1p3.

Yiting_Gong_4L

yes, the number before the hybridzation is the period that the element belongs in.

Yiting_Gong_4L

a sigma bond is stronger than a pi bond, therefore double bonds are stronger than single bonds.

Yiting_Gong_4L

Strongest to weakest
Ionic bond > covalent bond > hydrogen bond > dipole dipole force > London forces

Yiting_Gong_4L

A metallic bond is a bond between two metals ions :)

Yiting_Gong_4L

It might be better to calculate the formal charge of each atom so that you can choose the most stable structure.

Yiting_Gong_4L

Which elements can have expanded octets and why?

Yiting_Gong_4L

Lewis acid accepts electrons while Lewis base donates electrons.

Yiting_Gong_4L

Thank you for these practice problems!

Yiting_Gong_4L

Thank you for this explanation! This was very helpful.

Yiting_Gong_4L

I think that the octet or the half octet is the most stable.

Yiting_Gong_4L

Wavelength can also be converted from meters to nanometers and written in that unit.

Yiting_Gong_4L

H-bar is equal to h/2pi.

Yiting_Gong_4L

When would we use E=ch/wavelength instead of E=hv, vice versa?

Yiting_Gong_4L

I remember during lecture he explained electron shielding in a camping scenario. If you are sitting by a fire and someone walks in between you and the fire then you will feel less heat. Same scenario applies to electron shielding in that further electrons feel “less heat” or “less attraction” to the...

Yiting_Gong_4L

Yes, I'm pretty sure we will receive all of the formulas needed to take the test.

Yiting_Gong_4L

Constants do not have an affect on the amount of sig figs to use.

Yiting_Gong_4L

Thank you for the advice!!

Yiting_Gong_4L

I follow the order that is given in the problem.

Yiting_Gong_4L

I try to tell chemistry jokes, but there's no reaction.

Yiting_Gong_4L

Thank you! This was very helpful!

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