CHEMISTRY COMMUNITY

Maika Ngoie 1B

For a second order reaction the graph of ln[A] vs time will yield a straight line

Maika Ngoie 1B

It would probably only explicitly ask for half-life

Maika Ngoie 1B

They should be provided, but it may be easier to memorize which equation goes with which order.

Maika Ngoie 1B

Because concentration can never be a negative value, it is always positive.

Maika Ngoie 1B

Martina wrote:You can also look at units of the rate constant if it is given and be able to tell what the order is.

Yes! for zero order reactions the units are M/s. First order is s^-1, and second order is 1/M.s.

Maika Ngoie 1B

I always try to get there a bit earlier to calm my nerves, just helps familiarize myself with the testing area.

Maika Ngoie 1B

Step-up sessions are more like a step by step explanation of topics learned in class, specifically designed to essentially relearn material. Workshops, however are more focused on extra practice for topics.

Maika Ngoie 1B

me @Lavelle

Maika Ngoie 1B

Maika Ngoie 1B

Anushka Chauhan2B wrote:During disc

What about those whose discussion was cancelled?

Maika Ngoie 1B

Subashni Rajiv 1K wrote:Lyndon just posted practice problems for Electrochemistry and Kinetics that can be found if you search up ENDGAME.

Oh wow, thank you! I wonder how information will be relayed given circumstances.

Maika Ngoie 1B

Not sure, the format has yet to be announced, but given the circumstances I assume it will either be free response or maybe a bit of both.

Maika Ngoie 1B

WOW! I love this! Thank you so much Dr. Lavelle for being a professor that is not only passionate about what he is teaching, but is so clearly passionate about his students and teaching in general. Chemistry may be a hard science, but you have given me a strong foundation to learn on for the past tw...

Maika Ngoie 1B

Anushka Chauhan2B wrote:You should probs study it just in case

Also, considering the changes made to the final, I think it will be more based on new material.

Maika Ngoie 1B

I would study it, just in case, but considering that it was tested heavily on the midterm and we have covered a lot of new material, I would say it won't be too acid/base heavy, probably like 30% material from before the midterm and 70% since the midterm.

Maika Ngoie 1B

Van't Hoff's equation is used to relates changes in equilibrium to the change in temperature. So you can solve for Keq if you know the equilibrium constant of another reaction.

Maika Ngoie 1B

We may not have to draw the graphs, but we will probably need to know what graphs of first order, second order, and zeroth order reactions look like vs time.

Maika Ngoie 1B

In that instance, you would use Kp, Kc is used for molar concentration.

Maika Ngoie 1B

For me, something that always helps is to get to the test location early. Just helps calm my nerves about familiarizing and getting comfortable with the area. Also, when the testing begins, try not to focus too much on what everyone else is doing, and tune out anything that may be happening in the t...

Maika Ngoie 1B

In a reversible expansion, temperature is constant because the work is the sum of the infinitesimal small changes. Since these changes are really small, the energy lost from the system through work is instantly supplied with heat from the surroundings. Therefore, the temperature does not change for...

Maika Ngoie 1B

OPEN: both energy and matter transferred
CLOSED: energy but not matter transferred
ISOLATED: neither energy nor matter

Maika Ngoie 1B

Because in a closed system, matter cannot be transferred, but energy can.

Maika Ngoie 1B

In a calorimeter, energy and matter both CANNOT be transferred between the system and surroundings because of the tight seal, making it an isolated system

Maika Ngoie 1B

It's important to spot the difference because it'll help better understand the relationship between the system and surroundings and to understand the corresponding variables for each system (i.e. open system=constant pressure, among others)

Maika Ngoie 1B

No, neither energy nor matter can be transferred between a system and surroundings in an isolated system.

Maika Ngoie 1B

Aman Sankineni 2L wrote:Heat transfer to a system is positive, and heat transfer from a system is negative. W is positive if work is done by the system, and negative if work is done on the system.

So I would say that in this case, both are negative.

Maika Ngoie 1B

Open System: both matter and energy
Closed System: energy, but not matter
Isolated System: neither energy nor matter

Maika Ngoie 1B

An intensive property is a property in which the amount of material in a system does not affect its value or quantity. For an extensive property, however, the amount of material in a system does affect its value

Maika Ngoie 1B

A good tell for for reversible and irreversible is that irreversible reactions occur under constant pressure

Maika Ngoie 1B

Acids and bases, equilibrium, all of thermochemistry, and the first page of the thermodynamics concepts on lavelle's outline

Maika Ngoie 1B

I would use q=mC(deltaT) and honestly just plug in the information given

Maika Ngoie 1B

Technically, they could be used the same way in the equation, but H subscript c is the enthalpy of combustion.

Maika Ngoie 1B

Normally bond enthalpies should be stated, unless it is the most stable form of the naturally occurring element, in which case it does not have a bond enthalpy.

Maika Ngoie 1B

A state property is something (a quantity) that is independent of the path taken to reach a specific value or endpoint. Enthalpy is the total heat of a system and is also a state property.

Maika Ngoie 1B

Just to be safe, I would not assume anything if the problem doesn't state whether or not the reaction occurs under constant pressure

Maika Ngoie 1B

Delta H is only equal to qp under constant pressure considering that is what qp means, but the two should not be used interchangeable.

Maika Ngoie 1B

I think a good tell is whether or not the reaction occurs under constant pressure. That would make it an irreversible reaction.

Maika Ngoie 1B

Yup! The standard enthalpy of formation for products and/or reactants should be in kJ/mol

Maika Ngoie 1B

Yes, you multiply them each by their respective stoichiometric coefficient.

Maika Ngoie 1B

Vuong_2F wrote:Kc is the equilibrium constant when it's found using concentrations, while Kp is the equilibrium constant when it's found using partial pressures.

It's important to note that they are all calculated the same way

Maika Ngoie 1B

Le Chateliers principle is used any time a reaction at equalibrium is changed in any way

Maika Ngoie 1B

Not too sure but his outlines should let us know exactly what concepts we have to know for Test 1

Maika Ngoie 1B

Most likely just Outline 1 and 2

Maika Ngoie 1B

Pressure x Volume = Moles x Ideal Gas Constant x Temperature (in kelvin)

Maika Ngoie 1B

If the molecule had 1 or 2 lone pairs it would then become bent. If it had 3, that would make it linear

Maika Ngoie 1B

The difference between 2sp2 and sp2 is the statement of the energy level (n=2), but unless the question specifies that the energy level needs to be stated, then its not required.

Maika Ngoie 1B

Yes, because a pi bond requires a plane of symmetry for the bond to form and hold

Maika Ngoie 1B

they do not hybridize in pi double or triple bonds

Maika Ngoie 1B

Unless the question specifically asks for the energy level to be specified, sp2 should be fine

Maika Ngoie 1B

Lone pairs will make a bond angle less than (<) the angle of the shape it is derived from, because the electron repulsion from lone pairs condenses the angles of the bonds.

Maika Ngoie 1B

Yes, they are able to break the octet rule and have an expanded orbital

Maika Ngoie 1B

The VSEPR formula means the question is asking you to write out the AXE formula.

Maika Ngoie 1B

in a cis molecule the function groups are on the same side of the molecule, whereas in a trans molecule the function groups are on different sides. Another note, trans and cis molecules are actually isomers of each other.

Maika Ngoie 1B

The E is the number of lone pairs on the central atom

Maika Ngoie 1B

A t-shape molecule is derived from a trigonal bipyramidal but has 2 lone pairs and 3 bonds, making it resemble the letter T

Maika Ngoie 1B

A t-shape molecule is derived from a trigonal bipyramidal but has 2 lone pairs and 3 bonds, making it resemble the letter T

Maika Ngoie 1B

The VSEPR shape would be a better indication of polarity, a little trick to remember is that lone pairs will make a molecule polar, but it is always a good idea to draw the shape

Maika Ngoie 1B

The VSEPR for SO2 is AX2E because the central atom (S) is bonded to two oxygen atoms and has one lone pair.

Maika Ngoie 1B

1 or 2 lone pairs can create a bent shape

Maika Ngoie 1B

Looking at the number of lone pairs can help identify whether or not the molecule is bent or linear.

Maika Ngoie 1B

Technically XEF4, or any square planar is derived from an octahedral, but has two lone pairs. What makes it rare if the fact that the central atom has an expanded octet because it receives 4 bonds then has 2 lone pairs added on.

Maika Ngoie 1B

Once you can make the most stable lewis structure, the regions of electron density, and and the lone pairs, you should be able to correspond these numbers with a specific shape. You'll need to memorize the names and the characteristics for this one. For example, ammonia (NH3) has 3 regions of electr...

Maika Ngoie 1B

Lone pairs repel the other atoms within a molecule, compressing angles and making them smaller

Maika Ngoie 1B

In comparison to their interaction with the lone pairs of bonding pairs of other atoms, they stay together as the lone pairs cause repulsion

Maika Ngoie 1B

By removing the equatorial atoms, the space between remaining atoms is maximized with degree angles of 120 between 3 atoms and 90 between two

Maika Ngoie 1B

I would definitely review dipole--dipole, london dispersion, and hydrogen bonding, as those are the ones we focused on in class, however, I would also recommend looking over the others such as induced dipole-induced dipole etc.

Maika Ngoie 1B

Maika Ngoie 1B

If the most stable lewis structure is drawn, you will be able to properly determine the regions of electron density and the lone pairs which will then allow you to identify the correct VESPR shape

Maika Ngoie 1B

Lone Pair--Lone Pair > Lone Pair--Bonding > Bonding Pair--Bonding Pair

Maika Ngoie 1B

Polarity itself deals with the difference in electrically charged poles of a molecule, so if the charges do not cancel, we can assume they are not equally shared, meaning the molecule is polar.

Maika Ngoie 1B

I don't think the bond order is particularly important, in VESPR models we are looking more at the regions of electron density.

Maika Ngoie 1B

Yes, I believe we do. We will be tested on all of outline 4, and certain topics in outline 3

Maika Ngoie 1B

Lone Pair--Lone Pair > Lone Pair--Bonding > Bonding Pair--Bonding Pair

Maika Ngoie 1B

Lone pairs DO influence molecular shape, but only atom positions are used to name the actual shape.

Maika Ngoie 1B

Bond angles also cannot be calculated, per say, using VESPR, but it can help you determine in in terms of steric numbers. For example, we know that methane (CH4) is a tetrahedral, and all bond angles are 109.5, but ammonia (NH3) which has the same principle shape as methane, except now has a lone pa...

Maika Ngoie 1B

In a VESPR model, there is repulsion between lone pairs and bonding pairs. In terms of strength, LP--LP Bonds > LP--Bonding > Bonding--Bonding. Because atoms want to be spread out in VESPR models, the lone pairs cause an increased amount of repulsion.

Maika Ngoie 1B

While we generally view the trend (up and across to the right) as equally important, the truth is that going up has a bit of a greater effect on electronegativty than moving across a period. This is because the higher groups have less shells and therefore feel more pull from other atoms.

Maika Ngoie 1B

In a problem given to you, the valence electrons will normally be given as well because they vary

Maika Ngoie 1B

A molecule that has resonance has multiple lewis dot structures with double or triple bonds that can appear in multiple places, not necessarily that it has different lewis dot structures because chemical species that experience resonance technically have the same lewis structure, just different vers...

Maika Ngoie 1B

A good place to start is when looking at the number of electrons in a chemical species, and drawing the lewis dot structures, if a species is meant to have multiple bonds, the number of e- drawn should not match the total number of electrons needed.

Maika Ngoie 1B

By counting along the period, the number that represents element you are looking for will tell you the valence electrons. For example, Nitrogen is the 5th element in its period, and Florine is the 7th. However, Phosphorous is also has 5 valence electrons, but it is in a different period than Nitrogen.

Maika Ngoie 1B

This would be an important topic to know for the midterm! So when you look at the periodic table, electrons fill orbitals in that order. So since the elements that have 4s orbitals are in front of those that have valence electrons in the 3d state, they fill the 4s first. :) Over all, it's important...

Maika Ngoie 1B

Yes, there are a few exceptions to the general trends we see on the periodic table. Electronegativity increases as you move to the right of the PT from the metals up to the halogens, but the noble gases do not have electronegativities (unless forced under very extreme pressure/conditions) because t...

Maika Ngoie 1B

The relationship between the two lies with the fact that we use both Hund's Rule and the Pauli Exclusion Principle in conjunction with the Building-Up principle in order to properly create/write experimentally observed electron configurations.

Maika Ngoie 1B

The reason why Scandium is written as [Ar] 3d1 4s2 is because after the 20th element in the periodic table (Calcium), the 3d orbitals have a slightly lower energy than the 4s orbitals. Therefore, you would start filling the 3d orbitals until it is full. The 4s orbital is filled first because it is ...

Maika Ngoie 1B

Yes, there are nodal planes for all except the s- orbital. Just as the p- orbital has one nodal plane, the d- orbital has two, and so forth.

Maika Ngoie 1B

You can think of it similar to building structure, constructive interference is when the waves are in phase, almost providing support, creating a greater amplitude of the wavelength. Destructive, however, is when the wavelengths are out of phase and opposite to one another. This causes the energy of...

Maika Ngoie 1B

You usually divide by Avogadro's number when the question gives you the number of molecules and is asking you to find the number of moles of a compound. Remember that avagadro's number (6.626 x 10^23) is the number of molecules or atoms that are in a single mole, so by dividing by this number, you ...

Maika Ngoie 1B

Drake Choi_1I wrote:I remember learning in physics something about mediums and light. I know that a vacuum is where light can travel fastest. What is the next fastest medium?

I believe water is the next fastest at about 2.25 x 10^8 m.sec^-1, but we'll mainly be working with light in a vacuum

Maika Ngoie 1B

Throughout this quarter, and for the purpose of this class, the speed of light will remain a constant equal to 3.0 x 10^8 m.sec^-1, however outside of this setting, it is not so absolute, and actually changes relative to the the mediums it travels through.

Maika Ngoie 1B

The shape of the orbital is what determines how many electrons it can house. Electrons also must spin in different directions and because there are only two options, there can only be two electrons on each orbital. It is important to note that each level has a different number of orbitals (s=1, p=3,...

Maika Ngoie 1B

De Broglie's equation can be used to calculate the energy of anything with measurable wavelength properties OTHER THAN light. Typically speaking, a DeBroglie wavelength less than 10^-15 does not have detectable wavelength properties. Hope this helps!

Maika Ngoie 1B

Sometimes molarity and dilution problems can seem a bit wordy and overwhelming. For me, I always begin by writing down the number values that they give me and determining which are useful depending on what part of the problem I am at. That was I can interpret the real meaning of all the information ...

Maika Ngoie 1B

Rounding can be a bit tricky and if possible, I would keep the rounding to a minimum while you work out the problem. However, if you do, make sure to use the proper sig figs and your answer should be okay.

Maika Ngoie 1B

I think the equation you're referring to is the one where you subtract your lowest measured value from your highest value to record as precision, but I don't think we will be doing this with actual numerical values. I think it's more for us the understand the difference between the two and the indiv...

Maika Ngoie 1B

How are we supposed to know what number to multiply by in order to attain whole integers? Knowing if we need to multiply by 2 or 3 to reach a whole number is easy, but what about when the solution is more complicated? normally, the numbers should be pretty easy fractions, but if they turn out a lit...

Maika Ngoie 1B

Generally when rounding or using sig figs, looking at the original problem can help you gauge how many sig figs to use, and normally I would look at the LEAST precise measurement (the more decimal places the more precise). For example, if you are given a problem with the values 3.2, 5.72, and 0.32, ...

Search found 97 matches